© Cambridge University Press 2000, 2009. Bryophyte Biology provides an extensive overview of the hornworts, liverworts, and mosses; diverse groups of land plants that occupy a great variety of habitats throughout the world. This new edition covers essential aspects of bryophyte biology, from morphology, physiological ecology and conservation, to speciation, and genomics. Revised classifications incorporate contributions from recent phylogenetic studies. Six new chapters complement fully updated chapters from the original book to provide a completely up-to-date resource. New chapters focus on the contributions of Physcomitrella to plant genomic research, population ecology of bryophytes, mechanisms of drought tolerance, a phylogenomic perspective on land plant evolution, and problems and progress of bryophyte speciation and conservation. Written by leaders in the field, this book offers an authoritative treatment of bryophyte biology, with rich citation of the current literature, suitable for advanced students and researchers.
Peatlands harbour more than one-third of terrestrial carbon leading to the argument that the bryophytes, as major components of peatland ecosystems, store more organic carbon in soils than any other collective plant taxa. Plants of the genus Sphagnum are important components of peatland ecosystems and are potentially vulnerable to changing climatic conditions. However, the response of Sphagnum to rising temperatures, elevated CO2 and shifts in local hydrology have yet to be fully characterized. In this review, we examine Sphagnum biology and ecology and explore the role of this group of keystone species and its associated microbiome in carbon and nitrogen cycling using literature review and model simulations. Several issues are highlighted including the consequences of a variable environment on plant-microbiome interactions, uncertainty associated with CO2 diffusion resistances and the relationship between fixed N and that partitioned to the photosynthetic apparatus. We note that the Sphagnum fallax genome is currently being sequenced and outline potential applications of population-level genomics and corresponding plant photosynthesis and microbial metabolic modelling techniques. We highlight Sphagnum as a model organism to explore ecosystem response to a changing climate and to define the role that Sphagnum can play at the intersection of physiology, genetics and functional genomics.
The perceived low levels of genetic diversity, poor interspecific competitive and defensive ability, and loss of dispersal capacities of insular lineages have driven the view that oceanic islands are evolutionary dead ends. Focusing on the Atlantic bryophyte flora distributed across the archipelagos of the Azores, Madeira, the Canary Islands, Western Europe, and northwestern Africa, we used an integrative approach with species distribution modeling and population genetic analyses based on approximate Bayesian computation to determine whether this view applies to organisms with inherent high dispersal capacities. Genetic diversity was found to be higher in island than in continental populations, contributing to mounting evidence that, contrary to theoretical expectations, island populations are not necessarily genetically depauperate. Patterns of genetic variation among island and continental populations consistently fitted those simulated under a scenario of de novo foundation of continental populations from insular ancestors better than those expected if islands would represent a sink or a refugium of continental biodiversity. We, suggest that the northeastern Atlantic archipelagos have played a key role as a stepping stone for transoceanic migrants. Our results challenge the traditional notion that oceanic islands are the end of the colonization road and illustrate the significant role of oceanic islands as reservoirs of novel biodiversity for the assembly of continental floras.
Peat mosses (Sphagnum) are ecosystem engineers-species in boreal peatlands simultaneously create and inhabit narrow habitat preferences along two microhabitat gradients: an ionic gradient and a hydrological hummock-hollow gradient. In this article, we demonstrate the connections between microhabitat preference and phylogeny in Sphagnum. Using a dataset of 39 species of Sphagnum, with an 18-locus DNA alignment and an ecological dataset encompassing three large published studies, we tested for phylogenetic signal and within-genus changes in evolutionary rate of eight niche descriptors and two multivariate niche gradients. We find little to no evidence for phylogenetic signal in most component descriptors of the ionic gradient, but interspecific variation along the hummock-hollow gradient shows considerable phylogenetic signal. We find support for a change in the rate of niche evolution within the genus-the hummock-forming subgenus Acutifolia has evolved along the multivariate hummock-hollow gradient faster than the hollow-inhabiting subgenus Cuspidata. Because peat mosses themselves create some of the ecological gradients constituting their own habitats, the classic microtopography of Sphagnum-dominated peatlands is maintained by evolutionary constraints and the biological properties of related Sphagnum species. The patterns of phylogenetic signal observed here will instruct future study on the role of functional traits in peatland growth and reconstruction.
Reconstructing the origin and evolution of land plants and their algal relatives is a fundamental problem in plant phylogenetics, and is essential for understanding how critical adaptations arose, including the embryo, vascular tissue, seeds, and flowers. Despite advances in molecular systematics, some hypotheses of relationships remain weakly resolved. Inferring deep phylogenies with bouts of rapid diversification can be problematic; however, genome-scale data should significantly increase the number of informative characters for analyses. Recent phylogenomic reconstructions focused on the major divergences of plants have resulted in promising but inconsistent results. One limitation is sparse taxon sampling, likely resulting from the difficulty and cost of data generation. To address this limitation, transcriptome data for 92 streptophyte taxa were generated and analyzed along with 11 published plant genome sequences. Phylogenetic reconstructions were conducted using up to 852 nuclear genes and 1,701,170 aligned sites. Sixty-nine analyses were performed to test the robustness of phylogenetic inferences to permutations of the data matrix or to phylogenetic method, including supermatrix, supertree, and coalescent-based approaches, maximum-likelihood and Bayesian methods, partitioned and unpartitioned analyses, and amino acid versus DNA alignments. Among other results, we find robust support for a sister-group relationship between land plants and one group of streptophyte green algae, the Zygnematophyceae. Strong and robust support for a clade comprising liverworts and mosses is inconsistent with a widely accepted view of early land plant evolution, and suggests that phylogenetic hypotheses used to understand the evolution of fundamental plant traits should be reevaluated.
In diploid organisms, selfing reduces the efficiency of selection in removing deleterious mutations from a population. This need not be the case for all organisms. Some plants, for example, undergo an extreme form of selfing known as intragametophytic selfing, which immediately exposes all recessive deleterious mutations in a parental genome to selective purging. Here, we ask how effectively deleterious mutations are removed from such plants. Specifically, we study the extent to which deleterious mutations accumulate in a predominantly selfing and a predominantly outcrossing pair of moss species, using genome-wide transcriptome data. We find that the selfing species purge significantly more nonsynonymous mutations, as well as a greater proportion of radical amino acid changes which alter physicochemical properties of amino acids. Moreover, their purging of deleterious mutation is especially strong in conserved regions of protein-coding genes. Our observations show that selfing need not impede but can even accelerate the removal of deleterious mutations, and do so on a genome-wide scale.
Ferns are well known for their shade-dwelling habits. Their ability to thrive under low-light conditions has been linked to the evolution of a novel chimeric photoreceptor--neochrome--that fuses red-sensing phytochrome and blue-sensing phototropin modules into a single gene, thereby optimizing phototropic responses. Despite being implicated in facilitating the diversification of modern ferns, the origin of neochrome has remained a mystery. We present evidence for neochrome in hornworts (a bryophyte lineage) and demonstrate that ferns acquired neochrome from hornworts via horizontal gene transfer (HGT). Fern neochromes are nested within hornwort neochromes in our large-scale phylogenetic reconstructions of phototropin and phytochrome gene families. Divergence date estimates further support the HGT hypothesis, with fern and hornwort neochromes diverging 179 Mya, long after the split between the two plant lineages (at least 400 Mya). By analyzing the draft genome of the hornwort Anthoceros punctatus, we also discovered a previously unidentified phototropin gene that likely represents the ancestral lineage of the neochrome phototropin module. Thus, a neochrome originating in hornworts was transferred horizontally to ferns, where it may have played a significant role in the diversification of modern ferns.
Unraveling the macroevolutionary history of bryophytes, which arose soon after the origin of land plants but exhibit substantially lower species richness than the more recently derived angiosperms, has been challenged by the scarce fossil record. Here we demonstrate that overall estimates of net species diversification are approximately half those reported in ferns and ∼30% those described for angiosperms. Nevertheless, statistical rate analyses on time-calibrated large-scale phylogenies reveal that mosses and liverworts underwent bursts of diversification since the mid-Mesozoic. The diversification rates further increase in specific lineages towards the Cenozoic to reach, in the most recently derived lineages, values that are comparable to those reported in angiosperms. This suggests that low diversification rates do not fully account for current patterns of bryophyte species richness, and we hypothesize that, as in gymnosperms, the low extant bryophyte species richness also results from massive extinctions.
Unlike seed plants where global biogeographical patterns typically involve interspecific phylogenetic history, spore-producing bryophyte species often have intercontinental distributions that are best understood from a population genetic perspective. We sought to understand how reproductive processes, especially dispersal, have contributed to the intercontinental 'Pacific Rim' distribution of Sphagnum miyabeanum. In total, 295 gametophyte plants from western North America (California, Oregon, British Columbia, Alaska), Russia, Japan, and China were genotyped at 12 microsatellite loci. Nucleotide sequences were obtained for seven anonymous nuclear loci plus two plastid regions from 21 plants of S.miyabeanum and two outgroup species. We detected weak but significant genetic differentiation among plants from China, Japan, Alaska, British Columbia, and the western USA. Alaskan plants are genetically most similar to Asian plants, and British Columbian plants are most similar to those in the western USA. There is detectable migration between regions, with especially high levels between Alaska and Asia (China and Japan). Migration appears to be recent and/or ongoing, and more or less equivalent in both directions. There is weak (but significant) isolation-by-distance within geographical regions, and the slope of the regression of genetic on geographical distance differs for Asian versus North American plants. A distinctive Vancouver Island morphotype is very weakly differentiated, and does not appear to be reproductively isolated from plants of the normal morphotype. The intercontinental geographical range of S.miyabeanum reflects recent and probably ongoing migration, facilitated by the production of tiny spores capable of effective long distance dispersal. The results of the present study are consistent with Pleistocene survival of S.miyabeanum in unglaciated Beringia, although we cannot eliminate the possibility that the species recolonized Alaska from Asia more recently. © 2013 The Linnean Society of London.
UNLABELLED: • PREMISE OF THE STUDY: Sphagnum dominates vast expanses of wetland habitats throughout the northern hemisphere and species delimitation within the genus is important because floristic changes associated with a warming global climate may have measureable impacts on large-scale ecological processes. Most northern hemisphere peatmoss species (Sphagnum) have circumboreal ranges, but the Japanese species generally known as S. calymmatophyllum is endemic to Honshu Island. This prompted a population genetic and phylogenetic analysis to resolve the origin(s), population structure, and phylogenetic relationships of this morphologically variable species. • METHODS: Sixty plants collected from Mt. Gassan and Mt. Hakkoda were genotyped for 12 microsatellite loci. Two plastid loci and three anonymous nuclear loci were sequenced in a subset of the plants, plus representatives from 10 closely related species. • KEY RESULTS: Gametophytes exhibited fixed or nearly fixed heterozygosity at 9-10 of the 12 microsatellite loci. Two genetic groups were resolved by the microsatellite data, individuals showed no evidence of admixture, and the two groups of plants differ in morphology. They are heterozygous for different sets of alleles. The two taxa share plastid DNA sequences with two species that are common in Alaska. • CONCLUSIONS: Two taxa were distinguished: S. guwassanense and S. triseriporum. Both are allopolyploids; they originated independently from different but closely related progenitors. The maternal progenitor was likely either S. orientale or S. inexspectatum. The two allopolyploid taxa are heterozygous for (different) private microsatellite alleles, and one progenitor could be extinct.
A Holantarctic species, the inter-subgeneric allopolyploid Sphagnum ×falcatulum s.l. is a cryptic species complex composed of allodiploid and allotriploid cytotypes. The allotriploid plants are double allopolyploids (one of just two reported for bryophytes), with the allodiploid cytotype being one parent. Using a combination of microsatellites, nucleotide sequences, and morphological characters, allotriploid S. ×falcatulum is shown to be the most widespread Sphagnum species in the Holantarctic, with genetically documented populations in South America (Tierra del Fuego), New Zealand (South Island), and Australia (Macquarie Island, Tasmania). It is further concluded that six Sphagnum species described from the Tierra del Fuego Archipelago (TDF) of South America and a seventh described from South Island, New Zealand are synonymous with the allotriploid cytotype of S. ×falcatulum. The synonymized species include five named by Heikki Roivainen in 1937, S. ×ehyalinum, and S. subditivum. Allotriploid S. ×falcatulum is the predominant, perhaps the only, subgenus Cuspidata species present in TDF and immediate vicinity. The combination of low genetic diversity and an apparent absence of sexual reproduction indicate that the TDF population of the dioicous allotriploid S. ×falcatulum was likely founded by one or a limited number of individuals. The same is apparently the case for Macquarie I. and Tasmanian populations of allotriploid S. ×falcatulum. Several lines of evidence, including high genetic diversity, frequent sporophyte production, and the occurrence of the allodiploid parent, suggest that allotriploid S. ×falcatulum likely evolved in New Zealand. © British Bryological Society 2013.
Morphological characters from the gametophyte and sporophyte generations have been used in land plants to infer relationships and construct classifications, but sporophytes provide the vast majority of data for the systematics of vascular plants. In bryophytes both generations are well developed and characters from both are commonly used to classify these organisms. However, because morphological traits of gametophytes and sporophytes can have different genetic bases and experience different selective pressures, taxonomic emphasis on one generation or the other may yield incongruent classifications. The moss order Hookeriales has a controversial taxonomic history because previous classifications have focused almost exclusively on either gametophytes or sporophytes. The Hookeriales provide a model for comparing morphological evolution in gametophytes and sporophytes, and its impact on alternative classification systems. In this study we reconstruct relationships among mosses that are or have been included in the Hookeriales based on sequences from five gene regions, and reconstruct morphological evolution of six sporophyte and gametophyte traits that have been used to differentiate families and genera. We found that the Hookeriales, as currently circumscribed, are monophyletic and that both sporophyte and gametophyte characters are labile. We documented parallel changes and reversals in traits from both generations. This study addresses the general issue of morphological reversals to ancestral states, and resolves novel relationships in the Hookeriales.
The Hypnales are the largest order of mosses comprising approximately 4200 species. Phylogenetic reconstruction within the group has proven to be difficult due to rapid radiation at an early stage of evolution and, consequently, relationships among clades have remained poorly resolved. We compiled data from four sequence regions, namely, nuclear ITS1-5.8S-ITS2, plastid trnL-F and rps4, and mitochondrial nad5, for 122 hypnalean species and 34 species from closely related groups. Tree topologies from both Bayesian and parsimony analyses resolve the order as monophyletic. Although inferences were made from fastevolving genes, and despite strong phylogenetic signal in the nuclear ITS1-5.8S-ITS2 data, monophyly, as well as backbone nodes within the Hypnales, remains rather poorly supported except under Bayesian inferences. Ancestral distribution based on Bayesian dispersal-vicariance analysis supports a Gondwanan origin of the Hypnales and subsequent geographical radiation in the area of the former Laurasian supercontinent. Reconstruction of historical biogeography is congruent with mainly tropical and Gondwanan distributions in the sister groups Hypnodendrales, Ptychomniales, and Hookeriales, and with the dating for the oldest pleurocarp and hypnalean fossils. We contrast groupings in the phylogenetic tree with recent classifications and other phylogenetic inferences based on molecular data, and summarise current knowledge on the evolutionary history of, and relationships among, the Hypnales. © British Bryological Society 2012.
It is well accepted that the shape of the dispersal kernel, especially its tail, has a substantial effect on the genetic structure of species. Theory predicts that dispersal by fat-tailed kernels reshuffles genetic material, and thus, preserves genetic diversity during colonization. Moreover, if efficient long-distance dispersal is coupled with random colonization, an inverse isolation effect is predicted to develop in which increasing genetic diversity per colonizer is expected with increasing distance from a genetically variable source. By contrast, increasing isolation leads to decreasing genetic diversity when dispersal is via thin-tailed kernels. Here, we use a well-established model group for dispersal biology (peat mosses: genus Sphagnum) with a fat-tailed dispersal kernel, and the natural laboratory of the Stockholm archipelago to study the validity of the inverse isolation hypothesis in spore-dispersed plants in island colonization. Population genetic structure of three species (Sphagnum fallax, Sphagnum fimbriatum and Sphagnum palustre) with contrasting life histories and ploidy levels were investigated on a set of islands using microsatellites. Our data show (φst ', amova, IBD) that dispersal of the two most abundant species can be well approximated by a random colonization model. We find that genetic diversity per colonizer on islands increases with distance from the mainland for S. fallax and S. fimbriatum. By contrast, S. palustre deviates from this pattern, owing to its restricted distribution in the region, affecting its source pool strength. Therefore, the inverse isolation effect appears to hold in natural populations of peat mosses and, likely, in other organisms with small diaspores. © 2012 Blackwell Publishing Ltd.
• It has been proposed that long-distance dispersal of mosses to the Hawaiian Islands rarely occurs and that the Hawaiian population of the allopolyploid peat moss Sphagnum palustre probably resulted from a single dispersal event. • Here, we used microsatellites to investigate whether the Hawaiian population of the dioicous S. palustre had a single founder and to compare its genetic diversity to that found in populations of S. palustre in other regions. • The genetic diversity of the Hawaiian population is comparable to that of larger population systems. Several lines of evidence, including a lack of sporophytes and an apparently restricted natural distribution, suggest that sexual reproduction is absent in the Hawaiian plants. In addition, all samples of Hawaiian S. palustre share a genetic trait rare in other populations. Time to most recent ancestor (TMRCA) analysis indicates that the Hawaiian population was probably founded 49-51kyr ago. • It appears that all Hawaiian plants of S. palustre descend from a single founder via vegetative propagation. The long-term viability of this clonal population coupled with the development of significant genetic diversity suggests that vegetative propagation in a moss does not necessarily preclude evolutionary success in the long term. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.
Phylogenetic relationships in Daltoniaceae (∼200 species in 14 genera) are inferred from nucleotide sequences from five genes, representing all genomic compartments, using parsimony, likelihood and Bayesian methods. Alternative classifications for Daltoniaceae have favoured traits from either sporophytes or gametophytes; phylogenetic transitions in gametophytic leaf limbidia and sporophytic exostome ornamentation were evaluated using ancestral state reconstruction to assess the levels of conflict between these generations. Elimbate leaves and the cross-striate exostome are reconstructed as plesiomorphic states. Limbate leaves and papillose exostomes evolved at least two and six times, respectively, without reversals. The evolution of leaf limbidia is relatively conserved, but exostome ornamentation is highly homoplasious, indicating that superficial similarity in peristomes gives unreliable approximations of phylogenetic relatedness. Our phylogenetic analyses show that Achrophyllum and Calyptrochaeta are reciprocally monophyletic. Within core Daltoniaceae, relationships among taxa with elimbate leaves are generally well understood. However, taxa with limbate leaves form a monophyletic group, but resolved subclades correspond to biogeographical entities, rather than to traditional concepts of genera. Daltonia (∼21 species), Distichophyllum (∼100 species) and Leskeodon (∼20 species) are polyphyletic. Seven nomenclatural changes are proposed here. As the current taxonomy of Daltoniaceae lacks phylogenetic consistency, critical generic revisions are needed. © 2012 The Linnean Society of London.
A taxonomic treatment based on field studies, examination of herbarium collections, and previously published molecular data is provided for the North American species of the Sphagnum subsecundum complex. Sphagnum platyphyllum, S. contortum, S. lescurii, and S. subsecundum are gametophytically haploid. Sphagnum missouricum and S. carolinianum are gametophytically allodiploid. A single allodiploid population of S. platyphyllum and a homoploid (haploid) hybrid between S. contortum and S. subscundum, previously documented genetically, are described and illustrated (but neither distinguished taxonomically). Epitypes are designated from (haploid) S. lescurii and (allodiploid) S. missouricum because the ploidal level of the original type material cannot be determined unambiguously. In North America, S. subsecundum is restricted to the eastern part of the continent, as western plants named this species are not conspecific. North American plants named S. inundatum are considered synonymous with either S. lescurii (when haploid) or S. missouricum (when diploid). © 2012 by The American Bryological and Lichenological Society, Inc.
Climacium is a small but morphologically distinctive genus ("tree mosses") with four species distributed primarily in the Northern Hemisphere. Climacium dendroides occurs around the globe at northern latitudes with disjunct populations in Mexico and New Zealand, whereas C. americanum and C. kindbergii are endemic to eastern North America and C. japonicum is limited to eastern Asia. Using nucleotide sequence data from five plastid loci plus the nuclear ribosomal ITS region we assessed evidence for monophyly of taxonomic species and tested the hypothesis that C. americanum and C. kindbergii from eastern North America have a sister group relationship with C. japonicum from eastern Asia. Climacium japonicum is resolved as sister to a clade containing the circumboreal C. dendroides, C. americanum, and C. kindbergii. Climacium americanum and C. kindbergii were not resolved as monophyletic based on sequence data but together they composed the sister lineage to C. dendroides. Geographically disjunct populations of C. dendroides in Asia, Mexico, the United States, and Canada vary at only a few polymorphic nucleotide sites across the three loci. The disjunctive New Zealand plants of C. dendroides are related to Asian accessions. © 2012 by The American Bryological and Lichenological Society, Inc.
The application of genetic tools for studying species delimitation and relationships in Sphagnum (peatmosses) has demonstrated that evolutionary patterns are complex and include homoploid hybridization and multiple taxa of allopolyploid origin. We investigated evolutionary relationships in the so-called S. fimbriatum complex and tested hypotheses of species delimitation derived from patterns of morphological variation, and determined the origin of one species with diploid gametophytes. Plastid DNA sequences resolve a single haplotype shared by one described species, S. concinnum, and a morphotype that we had hypothesized to be another species (referred to informally as S. "diskoense"). All samples of the polyploid, S. tescorum, share an identical haplotype with most samples of S. girgensohnii. Sphagnum fimbriatum and S. girgensohnii share several plastid DNA haplotypes, and also share haplotypes with two other morphotypes that we had hypothesized to be distinct species (S. "obscurum" and S. "ubertum"). Fixed or nearly fixed heterozygosity at ten microsatellite loci show that S. tescorum is an allopolyploid. Genetic admixture analyses and computation of hybrid indices from microsatellite data, in combination with sequences from the plastid genome, support the hypothesis that S. fimbriatum and S. girgensohnii are progenitors of S. tescorum, with S. girgensohnii as the maternal parent. Data from 14 microsatellite loci demonstrate that S. concinnum, S. fimbriatum, S. girgensohnii, and S. tescorum are genetically distinct but the same data do not support separation of S. "diskoense," S. "obscurum," and S. "ubertum." Homoploid hybridization between S. fimbriatum and S. girgensohnii is strongly suggested by genetic data and phylogenetic analyses. © Copyright 2012 by the American Society of Plant Taxonomists.
Within Sphagnum cribrosum, a dioicous aquatic peatmoss, a unique morphological variant (the 'waveform'), found at only two lakes in North Carolina, has a branching architecture that is extremely differentiated from anything otherwise known in Sphagnum, although the plants are microscopically indistinguishable from S. cribrosum. At one site where the two morphologies co-occur, 60 years of field observations demonstrate the persistence of each morphology, even where the two forms grow intermixed. We conducted a reciprocal transplant experiment in which waveform and normal plants maintained their divergent morphologies for 8 months. We sampled populations throughout the range and conducted genetic and phylogenetic analyses with microsatellite markers and DNA sequences to investigate the genetic context of the waveform morphology within S. cribrosum. Haplotype networks from DNA sequences showed the two waveform populations are separated by 11 substitutions across three loci. Microsatellite analyses using nonparametric clustering and admixture models also indicated genetic dissimilarity between genotypes with waveform morphology at the two lakes. Both molecular datasets suggest that the waveform morphology had at least two independent origins, despite the proximity of the two lakes where it occurs uniquely. Given the clonal nature of the waveform, it is unlikely to form a cohesive evolutionary lineage deserving of taxonomic status. The analysis also revealed a genetically diverse population in Georgia as the potential source of variation found in all other populations of S. cribrosum. © 2012 The Linnean Society of London.
• Shifts in sexual systems are among the most common and important transitions in plants and are correlated with a suite of life-history traits. The evolution of sexual systems and their relationships to gametophyte size, sexual and asexual reproduction, and epiphytism are examined here in the liverwort genus Radula. • The sequence of trait acquisition and the phylogenetic correlations between those traits was investigated using comparative methods. • Shifts in sexual systems recurrently occurred from dioecy to monoecy within facultative epiphyte lineages. Production of specialized asexual gemmae was correlated to neither dioecy nor strict epiphytism. • The significant correlations among life-history traits related to sexual systems and habitat conditions suggest the existence of evolutionary trade-offs. Obligate epiphytes do not produce gemmae more frequently than facultative epiphytes and disperse by whole gametophyte fragments, presumably to avoid the sensitive protonemal stage in a habitat prone to rapid changes in moisture availability. As dispersal ranges correlate with diaspore size, this reinforces the notion that epiphytes experience strong dispersal limitations. Our results thus provide the evolutionary complement to metapopulation, metacommunity and experimental studies demonstrating trade-offs between dispersal distance, establishment ability, and life-history strategy, which may be central to the evolution of reproductive strategies in bryophytes.
Polyploidization is thought to result in instant sympatric speciation, but several cases of hybrid zones between one of the parental species and its polyploid derivative have been documented. Previous work showed that diploid Sphagnum lescurii is an allopolyploid derived from the haploids S. lescurii (maternal progenitor) and S. subsecundum (paternal progenitor). Here, we report the results from analyses of a population where allodiploid and haploid S. lescurii co-occur and produce sporophytes. We tested (i) whether haploids and diploids form hybrid triploid sporophytes; (ii) how hybrid and nonhybrid sporophytes compare in fitness; (iii) whether hybrid sporophytes form viable spores; (iv) the ploidy of any viable gametophyte offspring from hybrid sporophytes; (v) the relative viability of sporelings derived from hybrid and nonhybrid sporophytes; and (vi) if interploidal hybridization results in introgression between the allopolyploid and its haploid progenitor. We found that triploid hybrid sporophytes do occur and are larger than nonhybrid sporophytes, but exhibit very low germination percentages and produce sporelings that develop more slowly than those from nonhybrid sporophytes. All sporophytes attached to haploid gametophytes were triploid and were sired by diploid males, but all sporophytes attached to diploid gametophytes were tetraploid. This asymmetric pattern of interploidal hybridization is related to an absence of haploid male gametophytes in the population. Surprisingly, all sporelings from triploid sporophytes were triploid, yet were genetically variable, suggesting some form of aberrant meiosis that warrants further study. There was limited (but some) evidence of introgression between allodiploid and haploid S. lescurii.
The "bryophytes" comprise three phyla of plants united by a similar haploid-dominant life cycle and unbranched sporophytes bearing one sporangium: the liverworts (Marchantiophyta), mosses (Bryophyta), and hornworts (Anthocerophyta). Combined, these groups include some 20000 species. As descendents of embryophytes that diverged before tracheophytes appeared, bryophytes offer unique windows into the early evolution of land plants. We review insights into the evolution of plant life cycles, in particular the elaboration of the sporophyte generation, the major lineages within bryophyte phyla, and reproductive processes that shape patterns of bryophyte evolution. Recent transcriptomic work suggests extensive overlap in gene expression in bryophyte sporophytes vs. gametophytes, but also novel patterns in the sporophyte, supporting Bower's antithetic hypothesis for origin of alternation of generations. Major lineages of liverworts, mosses, and hornworts have been resolved and general patterns of morphological evolution can now be inferred. The life cycles of bryophytes, arguably more similar to those of early embryophytes than are those in any other living plant group, provide unique insights into gametophyte mating patterns, sexual conflicts, and the efficacy and effects of spore dispersal during early land plant evolution.
The evolution of land plants is tightly linked to the evolution of the alternation of generations. Because alternating ploidal generations share their genomes, investigating generation-biased gene expression can give insight into the evolution of life cycles in land plants. Toward this end, we describe gene expression differences associated with the alternation of isogenic sporophyte and gametophyte generations in bryophytes, extant representatives of early diverging land plants, using a moss model system (Funaria hygrometrica). We found that differentiation in gene expression between the sporophyte and gametophyte generations is weaker in the bryophyte model system than in Arabidopsis thaliana. This is in line with the basal phylogenetic position of bryophytes and with the origin of alternating generations from a purely haplontic life cycle. Comparative analysis of F. hygrometrica and A. thaliana gene expression data shows that there is limited conservation of generation-biased gene expression across land plants. However, genes showing shared sporophyte-biased expression in both F. hygrometrica and A. thaliana appear to be enriched for biological pathways representing critical molecular adaptations to terrestrial life. Comparative analyses of the expression of F. hygrometrica and A. thaliana regulatory genes suggest that conserved regulatory networks may be involved in growth and reproductive tissue development of the angiosperm and bryophyte sporophyte generations despite their morphological divergence. This study represents the first attempt to describe generation-biased gene expression in a plant with a well-developed sporophyte and gametophyte generations, and as such it lays the foundation for future targeted research on the developmental mechanisms underlying evolutionary diversification of plant sporophytes.
The distribution of Sphagnum cuspidatum has been subject to controversy. Although historically reported from all continents except Antarctica recent authors consider S. cuspidatum to be endemic to Europe and eastern North America. Microsatellites from Australian plants morphologically identified as S. cuspidatum were compared to microsatellites of plants morphologically identified as S. cuspidatum collected from other regions. The species was found to occur in Australia as well as on every continent except Antarctica. The sample most closely related to the Australian plants was collected in the Philippines, and samples from Australia, the Philippines, Colombia, and Equatorial Guinea formed a subclade within S. cuspidatum. Microsatellites further show that S. cuspidatum is one of the parental species of the double allopolyploid S. falcatulum, a Holantarctic species which is reported from Tasmania, New Zealand, and Chile. © Copyright 2011 by the American Society of Plant Taxonomists.
With approximately 200 species, the genus Radula is one of the most speciose genera of leafy liverworts. Although the genus is well delimited, its subdivision into subgenera and sections has been controversial. None of the subgeneric subdivisions have been the subject of an explicit test of internal consistency or monophyly based on molecular data and a comprehensive view of evolutionary relationships within the genus is thus still lacking. In the present paper we propose, based on a molecular phylogeny of the genus, a new subgeneric classification for Radula, and create three new subgenera. While the reconstructions of ancestral gametophytic characters allow for a morphological description of each of the seven lineages identified in our phylogeny, synapomorphies for these lineages are mostly lacking. Uncertainty of morphological state reconstructions at the deepest nodes of the phylogeny, which point to a rapid morphological diversification of the genus in its early history, do not allow for pinpointing when morphological changes occurred. The classification scheme proposed here is therefore mostly based on molecular features.
Genetic and morphological similarity between populations separated by large distances may be caused by frequent long-distance dispersal or retained ancestral polymorphism. The frequent lack of differentiation between disjunct conspecific moss populations on different continents has traditionally been explained by the latter model, and has been cited as evidence that many or most moss species are extremely ancient and slowly diverging. We have studied intercontinental differentiation in the amphi-Atlantic peat moss Sphagnum angermanicum using 23 microsatellite markers. Two major genetic clusters are found, both of which occur throughout the distributional range. Patterns of genetic structuring and overall migration patterns suggest that the species probably originated in North America, and seems to have been established twice in Northern Europe during the past 40,000 years. We conclude that similarity between S. angermanicum populations on different continents is not the result of ancient vicariance and subsequent stasis. Rather, the observed pattern can be explained by multiple long-distance dispersal over limited evolutionary time. The genetic similarity can also partly be explained by incomplete lineage sorting, but this appears to be caused by the short time since separation. Our study adds to a growing body of evidence suggesting that Sphagnum, constituting a significant part of northern hemisphere biodiversity, may be more evolutionary dynamic than previously assumed. © 2010 The Author(s). Evolution© 2010 The Society for the Study of Evolution.
Three species have been formerly segregated from Metzgeria in the genus Apometzgeria. One of the species, A. frontipilis, is endemic to South America but the second, A. pubescens, is currently understood as having a bipolar range with populations across the Holarctic and in southern South America. The third species, A. longifrondis, was described from China (and is not included in this study). Species of bryophytes that range across continents and have little or no morphological variation among populations may nevertheless harbor morphologically cryptic genetic lineages. We used nuclear and plastid sequence data to examine the phylogenetic relationship between Apometzgeria and Metzgeria, and phylogeographic patterns in taxa assigned to Apometzgeria. Two species often assigned to Apometzgeria are phylogenetically embedded within Metzgeria in two separate clades, one comprising all Holarctic A. pubescens and a second with A. pubescens from South America and all accessions of A. frontipilis. Phylogenetic and haplotype analyses reveal a lack of phylogeographic structure among A. pubescens plants from throughout its Holarctic distribution. However, A. pubescens in South America is more closely related to A. frontipilis and species of Metzgeria from South America than to any A. pubescens from the Northern Hemisphere. Thus, A. pubescens is Holarctic in distribution and morphologically similar plants form a divergent lineage in South America. Our results do not support Apometzgeria as a separate genus in the Metzgeriaceae. © 2011 by the American Bryological and Lichenological Society, Inc.
The monoicous peatmoss Sphagnum subnitens has a tripartite distribution that includes disjunct population systems in Europe (including the Azores), northwestern North America and New Zealand. Regional genetic diversity was highest in European S. subnitens but in northwestern North America, a single microsatellite-based multilocus haploid genotype was detected across 16 sites ranging from Coos County, Oregon, to Kavalga Island in the Western Aleutians (a distance of some 4115 km). Two multilocus haploid genotypes were detected across 14 sites on South Island, New Zealand. The microsatellite-based regional genetic diversity detected in New Zealand and North American S. subnitens is the lowest reported for any Sphagnum. The low genetic diversity detected in both of these regions most likely resulted from a founder event associated with vegetative propagation and complete selfing, with one founding haploid plant in northwest North America and two in New Zealand. Thus, one plant appears to have contributed 100% of the gene pool for the population systems of S. subnitens occurring in northwest North America, and this is arguably the most genetically uniform group of plants having a widespread distribution yet detected. Although having a distribution spanning 12.5° of latitude and 56° of longitude, there was no evidence of any genetic diversification in S. subnitens in northwest North America. No genetic structure was detected among the three regions, and it appears that European plants of S. subnitens provided the source for New Zealand and northwest North American populations. © 2010 Blackwell Publishing Ltd.
Islands have traditionally been considered as migratory and evolutionary dead ends for two main reasons: island colonizers are typically assumed to lose their dispersal power, and continental back colonization has been regarded as unlikely because of niche preemption. The hypothesis that islands might actually represent dynamic refugia and migratory stepping stones for species that are effective dispersers, and in particular, for spore-producing plants, is formally tested here, using the archipelagos of the Azores, Canary Islands, and Madeira, as a model. Population genetic analyses based on nuclear microsatellite variation indicate that dispersal ability of the moss Platyhypnidium riparioides does not decrease in the island setting. The analyses further show that, unlike island populations, mainland (southwestern Europe and North Africa) populations underwent a severe bottleneck during the last glacial maximum (LGM). Our results thus refute the traditional view of islands as the end of the colonization road and point to a different perception of North Atlantic archipelagos as major sources of biodiversity for the postglacial recolonization of Europe by spore-producing plants.
It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years. © 2011 Macmillan Publishers Limited All rights reserved.
Aim Bryophytes exhibit apparently low rates of endemism in Macaronesia and differ from angiosperms in their diversity patterns by the widespread occurrence of endemics within and among archipelagos. This paper investigates the phylogeography of the leafy liverwort Radula lindenbergiana to determine: (1) whether or not morphologically cryptic diversification has occurred in Macaronesia, and (2) the relationships between Macaronesian and continental populations. Location Macaronesia, Europe, Africa. Methods Eighty-four samples were collected across the species' distribution range and sequenced at four chloroplast DNA (cpDNA) loci (atpB-rbcL, trnG, trnL and rps4). Phylogenetic reconstructions and Bayesian ancestral area reconstructions were used in combination with population genetics statistics (H, NST, FST) to describe the pattern of present genetic diversity in R. lindenbergiana and infer its biogeographic history. Results Patterns of genetic diversity in R. lindenbergiana exhibit a striking westwards gradient, wherein haplotype (0.90) and nucleotide (0.0038±0.0019) diversity peak in Macaronesia, with a substantial endemic component. We found 20.9% of the genetic variance between biogeographic regions, and most pairwise FST comparisons between regions are significantly different from zero. The global NST (0.78) is significantly higher than the global FST (0.20), providing evidence for the presence of phylogeographic signal in the data. Ancestral area reconstructions suggest that the haplotypes currently found in western Europe share a Macaronesian common ancestor. Main conclusions The haplotype diversification exhibited by R. lindenbergiana in Macaronesia is comparable to that reported for many angiosperm groups at the species level. The apparent lack of radiation among Macaronesian bryophytes may thus reflect the reduced morphology of bryophytes in comparison with angiosperms. The high diversity found among Macaronesian haplotypes, especially in Madeira and the Canary Islands, and the significant NST/FST ratio between Macaronesia and all the other biogeographic regions (an indication that mutation rate exceeds dispersal rates) suggest that Macaronesian archipelagos could have served as a refugium during the Quaternary glaciations. Many haplotypes currently found in Europe share a Macaronesian common ancestor, and this further suggests that Macaronesia might have played a key role in the back-colonization of the continent. © 2010 Blackwell Publishing Ltd.
To better understand biogeographic patterns in the Southern Hemisphere, infraspecific molecular patterns were compared in two species of the moss genus Calyptrochaeta with contrasting distributions. One, C. apiculata, has a disjunct distribution encompassing South America and Australasia, and the other, C. asplenioides, occurs from South Africa northward to Rwanda and eastward into the Indian Ocean Islands. Nucleotide sequence data from two plastid loci (trnL-F and trnG) and nuclear ribosomal DNA (ITS12) were gathered from 62 samples representing the genera Calyptrochaeta and Daltonia (the latter as an outgroup), and subjected to phylogenetic analyses using maximum likelihood and Bayesian inference. The phylogenetic analyses revealed strong, geographically correlated structure within C. asplenioides in which populations from southern Africa are sister to those from eastern Africa, Madagascar, and the other Indian Ocean islands. Continental plants are further differentiated from island plants to the east. Divergence times suggest that C. asplenioides diversified in a time frame that does not support vicariance associated with continental drift, but rather dispersal, to explain the disjunct distribution of this species. Sequences of C. apiculata disjunct between Chile and Australia are nearly identical, which strongly suggests recent and/or ongoing gene flow. Our dating suggests that the South American-Australian disjunction of C. apiculata is also not old enough to reflect vicariance associated with continental drift. Thus, in both cases, recent long distance dispersal best explains their distributions in the Southern Hemisphere. © 2011 by the American Society of Plant Taxonomists.
UNLABELLED: • PREMISE OF THE STUDY: The Frullania tamarisci complex includes eight Holarctic liverwort species. One of these, F. asagrayana, is distributed broadly throughout eastern North America from Canada to the Gulf Coast. Preliminary genetic data suggested that the species includes two groups of populations. This study was designed to test whether the two groups are reproductively isolated biological species. • METHODS: Eighty-eight samples from across the range of F. asagrayana, plus 73 samples from one population, were genotyped for 13 microsatellite loci. Sequences for two plastid loci and nrITS were obtained from 13 accessions. Genetic data were analyzed using coalescent models and Bayesian inference. • KEY RESULTS: Frullania asagrayana is sequence-invariant at the two plastid loci and ITS2, but two clear groups were resolved by microsatellites. The two groups are largely reproductively isolated, but there is a low level of gene flow from the southern to the northern group. No gene flow was detected in the other direction. A local population was heterogeneous but displayed strong genetic structure. • CONCLUSIONS: The genetic structure of F. asagrayana in eastern North America reflects morphologically cryptic differentiation between reproductively isolated groups of populations, near-panmixis within groups, and clonal propagation at local scales. Reproductive isolation between groups that are invariant at the level of nucleotide sequences shows that caution must be exercised in making taxonomic and evolutionary inferences from reciprocal monophyly (or lack thereof) between putative species.
UNLABELLED: • PREMISE OF THE STUDY: The Sphagnopsida, an early-diverging lineage of mosses (phylum Bryophyta), are morphologically and ecologically unique and have profound impacts on global climate. The Sphagnopsida are currently classified in two genera, Sphagnum (peat mosses) with some 350-500 species and Ambuchanania with one species. An analysis of phylogenetic relationships among species and genera in the Sphagnopsida were conducted to resolve major lineages and relationships among species within the Sphagnopsida. • METHODS: Phylogenetic analyses of nucleotide sequences from the nuclear, plastid, and mitochondrial genomes (11 704 nucleotides total) were conducted and analyzed using maximum likelihood and Bayesian inference employing seven different substitution models of varying complexity. • KEY RESULTS: Phylogenetic analyses resolved three lineages within the Sphagnopsida: (1) Sphagnum sericeum, (2) S. inretortum plus Ambuchanania leucobryoides, and (3) all remaining species of Sphagnum. Sister group relationships among these three clades could not be resolved, but the phylogenetic results indicate that the highly divergent morphology of A. leucobryoides is derived within the Sphagnopsida rather than plesiomorphic. A new classification is proposed for class Sphagnopsida, with one order (Sphagnales), three families, and four genera. • CONCLUSIONS: The Sphagnopsida are an old lineage within the phylum Bryophyta, but the extant species of Sphagnum represent a relatively recent radiation. It is likely that additional species critical to understanding the evolution of peat mosses await discovery, especially in the southern hemisphere.
Global climate changes sometimes spark biological radiations that can feed back to effect significant ecological impacts. Northern Hemisphere peatlands dominated by living and dead peatmosses (Sphagnum) harbor almost 30% of the global soil carbon pool and have functioned as a net carbon sink throughout the Holocene, and probably since the late Tertiary. Before that time, northern latitudes were dominated by tropical and temperate plant groups and ecosystems. Phylogenetic analyses of mosses (phylum Bryophyta) based on nucleotide sequences from the plastid, mitochondrial, and nuclear genomes indicate that most species of Sphagnum are of recent origin (ca.
We investigated the phylogeny of a Holarctic-Asian group of Frullania species, the Frullania dilatata-F. appalachiana-F. eboracensis complex, using multiple accessions of morphologically circumscribed taxa and three molecular markers (nrITS region, cp DNA trnL-F and atpB-rbcL regions). Maximum parsimony and likelihood analyses indicated monophyly of morphologically defined taxa. Our phylogenies support a species rather than a subspecies concept within the complex, with four species in North America (F. appalachiana, F. eboracensis, F. parvistipula and F. virginica), and two species in Europe (F. dilatata and F. parvistipula). Accessions of F. dilatata from Southeast Europe and Asia are separated from other European accessions, indicating a former disjunct range of the species. © 2010 The Author(s).
The small, phylogenetically isolated liverwort genus Ptilidium has been regarded as of cool-Gondwanic origin with the bipolar, terrestrial Ptilidium ciliare giving rise to the Northern Hemisphere epiphytes Ptilidium pulcherrimum and Ptilidium californicum. This hypothesis is examined using a dataset including three chloroplast DNA regions from 134 Ptilidium accessions and one accession each of its closest relatives Trichocoleopsis and Neotrichocolea. Maximum likelihood and parsimony analyses point to a close relationship between P. ciliare and P. pulcherrimum, whereas P. californicum is placed sister to the remainder of the genus, separated by a long branch. Haplotype analysis and our phylogeny indicate the presence of Southern Hemisphere haplotypes of P. ciliare in the Northern Hemisphere, and shared haplotypes of P. ciliare and P. pulcherrimum between Europe and North America. Based on our findings, we reject the Gondwana-scenario and propose recent long distance dispersal as an explanation for the bipolar disjunct range. Ptilidium ciliare is resolved as paraphyletic with P. pulcherrimum nested within it. An isolated Ptilidium lineage with the morphology of P. ciliare from the Himalaya region likely represents a hitherto unrecognized cryptic species. Ptilidium pulcherrimum splits into a Japanese clade and a clade with accessions from Europe and North America. © 2010 Elsevier Inc.
It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years.Heredity advance online publication, 18 August 2010; doi:10.1038/hdy.2010.96.
Genetic diversity and structure are described in the aquatic moss Platyhypnidium riparioides to assess its dispersal ability at a regional scale and to determine whether patterns of genetic differentiation correlate with environmental variation. Variation at six nuclear microsatellite loci from 50 populations in southern Belgium was investigated through Mantel tests, partial Mantel tests and spatial analysis of molecular variance. Overall patterns of genotypic variation showed strong differentiation among populations at a regional scale (FST = 0.57). The high values of FIS observed within populations at both the ramet and genet levels, and the higher proportion of ramets with the same genotype than expected by chance, all point to a strongly clonal or selfing mating system. A genetic discontinuity was identified between northern and southern groups of populations. Within each group, FST and geographical distances were significantly correlated. Partial Mantel tests suggest that genetic and ecological distances are significantly correlated in the southern group. The results point to strong dispersal limitation at the landscape scale and suggest that the southern and northern groups experienced different histories. Within the former, the correlation between genetic and ecological variation is suggestive of reproductive isolation among ecotypes. © 2009 New Phytologist.
Frullania tamarisci is usually regarded as a polymorphic, holarctic-Asian liverwort species with four allopatric subspecies [subsp. asagrayana, moniliata, nisquallensis and tamarisci]. This hypothesis is examined using a dataset including sequences of the nuclear internal transcribed spacer region and the plastid trnL- trnF and atpB- rbcL regions of 88 accessions of F. tamarisci and putatively related taxa. Maximum parsimony and maximum likelihood analyses indicate the presence of at least eight main lineages within F. tamarisci s. l. The long branches leading to the tip nodes of the different F. tamarisci s. l. clades and their partly sympatric distribution reinforce species rank. Within F. tamarisci s. l. we recognize the Asian F. moniliata, the western North American F. californica and F. nisquallensis, the eastern North American F. asagrayana, the eastern North American-European F. tamarisci s. str., the Macaronesian F. sergiae, and two newly identified European lineages assigned to as F. calcarifera and F. tamarisci var. azorica. The considerable sequence differences are not reflected in conspicuous morphological disparities, rendering F. tamarisci s. l. the most explicit example of a complex of semi-cryptic and cryptic liverwort species. The temperate Frullania clades of this study likely went through recent extinction and expansion processes as indicated by the bottleneck pattern of genetic diversity. Species from tropical regions or regions with an Atlantic climate usually contain several geographical lineages. Our findings support frequent short-distance migration, rare successful long-distance dispersal events, extinction and recolonization as an explanation for the range formation in these Frullania species. © 2010 Elsevier Inc.
This study provides the first report that Sphagnum mendocinum (Sphagnum section Cuspidata) and S. papillosum (Sphagnum section Sphagnum) are allopolyploids. Sphagnum mendocinum is an intersectional allopolyploid, with parental species from Sphagnum sections Cuspidata and Subsecunda. It is the third intersectional alloploid species reported for Sphagnum. The gametophytically allodiploid cytotype of S. papillosum was detected in Europe, North America, and Japan. It appears to be the predominant, if not the only, cytotype for this species. Our results may warrant re-examination of the report of a haploid (n = x) cytotype for S. papillosum. © 2010 by The American Bryological and Lichenological Society, Inc.
Adelanthaceae (including Jamesoniellaceae) represent a major lineage of jungermannialean liverworts that is characterized by ventral-intercalary, often flagelliform branches, succubous leaves, ovoid to cylindrical, plicate perianths with a contracted mouth, often connate bracts and bracteoles, and 4-7 stratose capsule walls. Here we present the first comprehensive molecular phylogeny of Adelanthaceae using five markers (rbcL, psbA, trnL-trnF region, atpB-rbcL spacer, nrITS1-5.8S-ITS2) and 108 accessions from throughout the geographic range of the family. The molecular data support the separation of subfamilies Adelanthoideae and Jamesonielloideae. The Adelanthoideae include the genera Adelanthus, Pseudomarsupidium and Wettsteinia. The Jamesonielloideae include representatives of the genera Anomacaulis, Cryptochila, Cuspidatula, Jamesoniella, and Syzygiella in five main clades. The monophyly of taxa in current morphological classification schemes of Jamesonielloideae is not supported by the molecular data. Based on the outcome of the molecular phylogenetic analyses we propose to include Anomacaulis and Jamesoniella kirkii in Cuspidatula, and to place Cryptochila, Roivainenia, and Jamesoniella in the synonymy of Syzygiella. Molecular data support intercontinental ranges for several species and a range formation of Adelanthaceae by frequent short-distance dispersal, rare long-distance dispersal, extinction, and diversification. Disjunct distribution patterns within the Adelanthaceae cannot be explained by Gondwanan vicariance. © 2009 Elsevier Inc. All rights reserved.
Several complexes of species in Sphagnum (peat mosses) originated through hybridization and allopolyploidy, suggesting that these processes have played a major evolutionary role in this genus. The Sphagnum subsecundum complex includes gametophytically haploid and diploid species in North America. Analyses of 12 microsatellite loci and sequences from two plastid DNA markers show that the evolutionary history of this group is substantially more complex than previously thought. Two taxonomic species, Sphagnum lescurii and Sphagnum inundatum, include both haploid and diploid populations. Within each ploidal level, S. lescurii and S. inundatum are not genetically differentiated. The diploid taxa show patterns of fixed heterozygosity for the microsatellite markers, consistent with an allopolyploid origin. Diploid S. lescurii is an allopolyploid between haploid S. lescurii and (haploid) S. subsecundum. Sphagnum carolinianum is an allopolyploid between haploid S. lescurii and an unknown parent. We detected homoploid hybridization between the haploids Sphagnum contortum and S. subsecundum. Finally, we report three samples of diploid Sphagnum platyphyllum (otherwise haploid) that have an allopolyploid origin involving north-eastern haploid S. platyphyllum and an unidentified taxon. © 2010 The Linnean Society of London.
Multiple paternity (polyandry) frequently occurs in flowering plants and animals and is assumed to have an important function in the evolution of reproductive traits. Polyandry in bryophytes may occur among multiple sporophytes of a female gametophyte; however, its occurrence and extent is unknown. In this study we investigate the occurrence and extent of multiple paternity, spatial genetic structure, and sporophytic inbreeding depression in natural populations of a dioicous bryophyte species, Sphagnum lescurii, using microsatellite markers. Multiple paternity is prevalent among sporophytes of a female gametophyte and male genotypes exhibit significant skew in paternity. Despite significant spatial genetic structure in the population, suggesting frequent inbreeding, the number of inbred and outbred sporophytes was balanced, resulting in an average fixation coefficient and population level selfing rate of zero. In line with the prediction of sporophytic inbreeding depression sporophyte size was significantly correlated with the level of heterozygosity. Furthermore, female gametophytes preferentially supported sporophytes with higher heterozygosity. These results indicate that polyandry provides the opportunity for postfertilization selection in bryophytes having short fertilization distances and spatially structured populations facilitating inbreeding. Preferential maternal support of the more heterozygous sporophytes suggests active inbreeding avoidance that may have significant implications for mating system evolution in bryophytes.
In organisms with haploid-dominant life cycles, natural selection is expected to be especially effective because genetic variation is exposed directly to selection. However, in spore-producing plants with high dispersal abilities, among-population migration may counteract local adaptation by continuously redistributing genetic variability. In this study, we tested for adaptation at the molecular level by comparing nucleotide polymorphism in two genes (GapC and Rpb2) in 10 European populations of the peatmoss species, Sphagnum fimbriatum with variability at nine microsatellite loci assumed to be selectively neutral. In line with previous results, the GapC and Rpb2 genes showed strikingly different patterns of nucleotide polymorphism. Neutrality tests and comparison of population differentiation based on the GapC and Rpb2 genes with neutrally evolving microsatellites using coalescent simulations supported non-neutral evolution in GapC, but neutral evolution in the Rpb2 gene. These observations and the positions of the replacement mutations in the GAPDH enzyme (coded by GapC) indicate a significant impact of replacement mutations on enzyme function. Furthermore, the geographic distribution of alternate GapC alleles and/or linked genomic regions suggests that they have had differential success in the recolonization of Europe following the Last Glacial Maximum.
Pohlia flexuosa is reported from a single California site as new for the North American moss flora. This species is otherwise found in central and eastern Asia, where it is one of the most common gemmiferous Pohlia species, and in western Europe. A key is provided for the six gemmiferous species of Pohlia currently known from California. Copyright ©2009 by The American Bryological and Lichenological Society, Inc.
The California endemic species described as Schiymenium shevockii A. J. Shaw is transferred to the genus Mielichhoferia because phylogenetic analyses have shown that peristome structure (exostomial versus endostomial) is not a reliable character for distinguishing these two genera. Copyright © 2009 by The American Bryological and Lichenological Society, Inc.
Seed plant genera often exhibit intercontinental disjunctions where different species are found on different continents. Many morphologically circumscribed bryophyte species exhibit similar disjunctions. We used nucleotide sequences from the plastid and nuclear genomes to test hypotheses of phylogeography within representatives of the genus Metzgeria: Metzgeria furcata, Metzgeria conjugata, and Metzgeria myriopoda. The first two species have sexual and asexual populations, exhibit disjunctions between North America and Europe, and have been split into separate species, numerous subspecies or varieties. The third species occurs in eastern North America but is not reported from Europe. Phylogenetic analyses resolved three distinct lineages within the morphologically defined species, M. furcata: one in North America, and two in Europe. Similarly, three morphologically cryptic clades of M. conjugata were resolved by the molecular data: northern North America, Europe, and south-eastern North America. For both species, molecular divergence among taxa occurred in the absence of morphological change. In the case of M. myriopoda, all plants from eastern North America were both morphologically uniform and genetically homogeneous (although not identical). The present study provides significant insight into a plant group with complex taxonomy, and indicates that these liverwort taxa with wide distributions, extreme sex ratios, and continental disjunctions harbor cryptic lineages. © 2009 The Linnean Society of London.
This paper documents the occurrence of allotriploidy (having three differentiated genomes) in gametophytes of two Southern Hemisphere Sphagnum species (S. australe, S. falcatulum). The pattern of microsatellite alleles indicates that both species are composed of a complex of allodiploid and allotriploid gametophytes, with the latter resulting from two allopolyploidization events. No haploid (n = x) gametophytes were found for either species. The ploidal levels suggested by the pattern of microsatellite alleles were confirmed by flow cytometry and Feulgen DNA image densitometry. For both S. australe and S. falcatulum, the respective allodiploid plants (or their ancestors) are one of the parent species of the allotriploid plants. This is the first report of triploidy in Sphagnum gametophytes occurring in nature and also the first report of the presence of three differentiated genomes in any bryophyte. It is also the first report of intersectional allopolyploidy in Sphagnum, with S. australe appearing to have parental species from Sphagnum sections Rigida and Sphagnum, and S. falcatulum having parental species from Sphagnum sections Cuspidata and Subsecunda. In both species, the allotriploid cytotypes were the most prevalent cytotype on the South Island of New Zealand. The pattern of microsatellite alleles shows the presence of two genetically distinct populations of allodiploid S. australe, possibly indicating multiple origins of polyploidy for that allodiploid cytotype. Morphological evidence is also highly indicative of recurrent polyploidy in the allotriploid cytotype of S. falcatulum. Allopolyploidy has clearly played a major evolutionary role in these two Southern Hemisphere taxa. This study, in conjunction with other recent research, indicates that allopolyploidy is a common, if not the predominant, form of polyploidy in Sphagnum. © 2009 Blackwell Publishing Ltd.
Microsatellite markers were used to test whether two recently described species of Sphagnum (Bryophyta), S. atlanticum R.E. Andrus and S. bergianum R.E. Andrus, represent distinct gene pools. The first species is considered endemic to eastern North America while the second species has been reported from Alaska and Newfoundland. The results indicate that S. atlanticum does not differ genetically from the closely related species, S. torreyanum , also restricted to eastern North America. In fact, some samples that are identical across all 15 microsatellite loci have been distinguished morphologically as these two species. Plants of S. bergianum from Alaska are closely related genetically to Alaskan plants of the similar species, S. subfulvum , whereas Newfoundland plants of S. bergianum are more closely related to Newfoundland plants of S. subfulvum . Alaskan versus Newfoundland plants of S. subfulvum s.l. (including S. bergianum ) are differentiated at microsatellite loci. Another closely related species, S. subnitens , is distinct from S. subfulvum and S. bergianum . Sphagnum atlanticum is synonymized under S. torreyanum and S. bergianum is synonymized under S. subfulvum © Copyright 2009.
Several lines of evidence suggest that recent long-distance dispersal may have been important in the evolution of intercontinental distribution ranges of bryophytes. However, the absolute rate of intercontinental migration and its relative role in the development of certain distribution ranges is still poorly understood. To this end, the genetic structure of intercontinental populations of six peatmoss species showing an amphi-Atlantic distribution was investigated using microsatellite markers. Methods relying on the coalescent were applied (IM and MIGRATE) to understand the evolution of this distribution pattern in peatmosses. Intercontinental populations of the six peatmoss species were weakly albeit significantly differentiated (average F(ST) = 0.104). This suggests that the North Atlantic Ocean is acting as a barrier to gene flow even in bryophytes adapted to long-range dispersal. The im analysis suggested a relatively recent split of intercontinental populations dating back to the last two glacial periods (9000-289,000 years ago). In contrast to previous hypotheses, analyses indicated that both ongoing migration and ancestral polymorphism are important in explaining the intercontinental genetic similarity of peatmoss populations, but their relative contribution varies with species. Migration rates were significantly asymmetric towards America suggesting differential extinction of genotypes on the two continents or invasion of the American continent by European lineages. These results indicate that low genetic divergence of amphi-Atlantic populations is a general pattern across numerous flowering plants and bryophytes. However, in bryophytes, ongoing intercontinental gene flow and retained shared ancestral polymorphism must both be considered to explain the genetic similarity of intercontinental populations.
Allopolyploidy is probably the most extensively studied mode of plant speciation and allopolyploid species appear to be common in the mosses (Bryophyta). The Sphagnum subsecundum complex includes species known to be gametophytically haploid or diploid, and it has been proposed that the diploids (i.e., with tetraploid sporophytes) are allopolyploids. Nucleotide sequence and microsatellite variation among haploids and diploids from Newfoundland and Scandinavia indicate that (1) the diploids exhibit fixed or nearly fixed heterozygosity at the majority of loci sampled, and are clearly allopolyploids, (2) diploids originated independently in North America and Europe, (3) the European diploids appear to have the haploid species, S. subsecundum, as the maternal parent based on shared chloroplast DNA haplotypes, (4) the North American diploids do not have the chloroplast DNA of any sampled haploid, (5) both North American and European diploids share nucleotide and microsatellite similarities with S. subsecundum, (6) the diploids harbor more nucleotide and microsatellite diversity than the haploids, and (7) diploids exhibit higher levels of linkage disequilibrium among microsatellite loci. An experiment demonstrates significant artifactual recombination between interspecific DNAs coamplified by PCR, which may be a complicating factor in the interpretation of sequence-based analyses of allopolyploids.
Eight microsatellite loci from the aquatic moss Platyhypnidium riparioides were identified using the method of microsatellite-enriched libraries. Polymorphism was assessed in a sample of four populations of 20 individuals each from four streams of the Meuse hydrographic basin in southern Belgium. The markers amplified three to seven alleles per locus. Comparison of observed and expected heterozygosities as well as F-statistics (F(ST) = 0.62) reveals a significant genetic differentiation among populations. These markers will be useful for further investigation of population genetic structure and diversity at different nested spatial scales.
Liverworts harbor diverse fungi, including endophytes, in their healthy tissues. To address whether patterns of endophyte diversity are correlated with host phylogeny or geography, we designed a broad geographic survey with controlled phylogenetic host sampling. We collected liverworts in North Carolina, Washington, Idaho, British Columbia, Germany, and New Zealand and identified endophytes using culture-based and molecular methods. Of the major lineages of filamentous ascomycetes recovered, 53-88% belonged to the Xylariales. Endophyte accumulation curves did not saturate, and singleton sequences were dominant in each region, suggesting that liverwort endophyte communities are diverse. There was no significant difference in species richness between regional endophyte communities; however, total richness estimators indicated that North Carolina and New Zealand have richer communities than do Germany and the Pacific Northwest. This pattern reflects lower per-host endophyte density and prevalence of a common, shared sequence group in Germany and the Pacific Northwest. Although species richness was relatively low in the Pacific Northwest, the greatest phylogenetic diversity of endophytes was recovered there. Tests for regional and host specificity revealed that endophyte floras of hosts within a geographic area are more similar to one another than to those of closely related hosts. Geographic distance, not host phylogeny, best explains differences among communities.
Divergent populations are intrinsically reproductively isolated when hybrids between them either fail to develop properly or do not produce viable offspring. Intrinsic isolation may result from Dobzhansky-Muller (DM) incompatibilities, in which deleterious interactions among genes or gene products lead to developmental problems or underdominant chromosome structure differences between the parents. These mechanisms can be tested by studying marker segregation patterns in a hybrid mapping population. Here we examine the genetic basis of abnormal development in hybrids between two geographically distant populations of the moss Ceratodon purpureus. Approximately half of the hybrid progeny exhibited a severely reduced growth rate in early gametophyte development. We identified four unlinked quantitative trait loci (QTL) that interacted asymmetrically to cause the abnormal development phenotype. This pattern is consistent with DM interactions. We also found an excess of recombination between three marker pairs in the abnormally developing progeny, relative to that estimated in the normal progeny. This suggests that structural differences in these regions contribute to hybrid breakdown. Two QTL coincided with inferred structural differences, consistent with recent theory suggesting that rearrangements may harbor population divergence alleles. These observations suggest that multiple complex genetic factors contribute to divergence among populations of C. purpureus.
A seemingly obvious but sometimes overlooked premise of any evolutionary analysis is delineating the group of taxa under study. This is especially problematic in some bryophyte groups because of morphological simplicity and convergence. This research applies information from nucleotide sequences for eight plastid and nuclear loci to delineate a group of northern hemisphere peat moss species, the so-called Sphagnum subsecundum complex, which includes species known to be gametophytically haploid or diploid (i.e., sporophytically diploid-tetraploid). Despite the fact that S. subsecundum and several species in the complex have been attributed disjunct ranges that include all major continents, phylogenetic analyses suggest that the group is actually restricted to Europe and eastern North America. Plants from western North America, from California to Alaska, which are morphologically similar to species of the S. subsecundum complex in eastern N. America and Europe, actually belong to a different deep clade within Sphagnum section Subsecunda. One species often considered part of the S. subsecundum complex, S. contortum, likely has a reticulate history involving species in the two deepest clades within section Subsecunda. Nucleotide sequences have a strong geographic structure across the section Subsecunda, but shallow tip clades suggest repeated long-distance dispersal in the section as well.
© Cambridge University Press 2000, 2009. Introduction The three lineages of bryophytes, mosses, liverworts, and hornworts, compose successful groups of early embryophytes. The mosses are estimated to include some 12 700 species (Crosby et al. 2000), the liverworts approximately 6000–8000 extant species (Crandall-Stotler & Stotler 2000, Chapter 1, this volume), and the hornworts about 100–150 species (Chapter 3, this volume). Mosses are comparable in species richness to the monilophytes, which are estimated to include about 11 500 species (Pryer et al. 2004). Among the extant land plants, therefore, only the angiosperms are currently more species-rich than are the bryophytes. I. is often stated that bryophytes are most diverse in the tropics and fit the general pattern found in many groups of organisms, with increasing species richness toward the equator (Rosenzweig 1995). However, a quantitative analysis of latitudinal diversity patterns in the mosses failed to detect any such latitudinal gradient, except perhaps a weak one in the Americas (Shaw et al. 2005a). I. appears that liverwort diversity is highest at moderate to high latitudes of the Southern Hemisphere, although one family, the Lejeuneaceae, is hyperdiverse in wet tropical forests of both the New and Old Worlds (Gradstein 1979). The fossil record for mosses, liverworts, and hornworts is too incomplete to assess whether these groups were more or less diverse in the geological past (Miller 1984, Oostendorp 1987).
© Cambridge University Press 2000, 2009. With approximately 13 000 species, the Bryophyta compose the second most diverse phylum of land plants. Mosses share with the Marchantiophyta and Anthocerotophyta a haplodiplobiontic life cycle that marks the shift from the haploid-dominated life cycle of the algal ancestors of embryophytes to the sporophyte-dominated life cycle of vascular plants. The gametophyte is free-living, autotrophic, and almost always composed of a leafy stem. Following fertilization a sporophyte develops into an unbranched axis bearing a terminal spore-bearing capsule. The sporophyte remains physically attached to the gametophyte and is at least partially physiologically dependent on the maternal plant. Recent phylogenetic reconstructions suggest that three lineages of early land plants compose an evolutionary grade that spans the transition to land and the origin of plants with branched sporophytes (see Chapter 4). The Bryophyta seem to occupy an intermediate position: their origin predates the divergence of the ancestor to the hornworts and vascular plants but evolved from a common ancestor with liverworts (Qiu et al. 2006). The origin of the earliest land plants can be traced back to the Ordovician and maybe the Cambrian (Strother et al. 2004). Although unambiguous fossils of mosses have only been recovered from sediments dating from younger geological periods (Upper Carboniferous), divergence time estimates based on molecular phylogenies suggest that the origin of mosses dates back to the Ordovician (Newton et al. 2007) and thus that their unique evolutionary history spans at least 400 million years.
Allopolyploid speciation is likely the predominant mode of sympatric speciation in plants. The Sphagnum subsecundum complex includes six species in North America. Three have haploid gametophytes, and three are thought to have diploid gametophytes. Microsatellite analyses indicated that some plants of S. inundatum and S. lescurii are heterozygous at most loci, but others have only one allele at each locus. Flow cytometry and Feulgen staining showed that heterozygous plants have twice the genome size as plants with one allele per locus; thus, microsatellite patterns can be used to survey the distribution and abundance of haploid and diploid gametophytes. Microsatellite analyses also revealed that S. carolinianum is consistently diploid, but S. lescurii and S. inundatum include both haploid and diploid populations. The frequency of diploid plants in S. lescurii increases with latitude. In an analysis of one population of S. lescurii, both cytotypes co-occurred but were genetically differentiated with no evidence of interbreeding. The degree of genetic differentiation showed that the diploids were not derived from simple genome duplication of the local haploids. Heterozygosity appears to be fixed or nearly so in diploids, strongly suggesting that although morphologically indistinguishable from the haploids, they are derived by allopolyploidy.
A new species of Sphagnum section Subsecunda, S. beringiense, is described from arctic Alaska from the vicinity of Barrow along the northern coast. The species is distinguished morphologically by the light, yellow-green color of the gametophytes, multistratose stem cortex with 2-4 layers of enlarged thin-walled cells, round, medium-size (ca. 5 μm diameter) outer branch leaf pores, scattered inner branch leaf pores, typically few outer stem leaf pores, and abundant, round to elliptic inner stem leaf pores. Two unique plastid DNA haplotypes occur among Barrow area plants of S. beringiense, and these differ by a minimum of three nucleotide substitutions from those of other Alaskan Sphagnum species in the section Subsecunda. Microsatellite markers show that S. beringiense is genetically variable despite the fact that all plants were sampled from within an area of a few km2 and neither gametangia nor sporophytes have been observed. A key to the six Alaskan species of Sphagnum section Subsecunda is provided. © Copyright 2008 by the American Society of Plant Taxonomists.
Phylogenetic relationships among the seven genera of the Hypopterygiaceae, represented by 14 of the 21 species recognized in the family, were reconstructed based on variation in nucleotide sequences of six nuclear, mitochondrial, and plastid loci. Monophyly of the Hypopterygiaceae is strongly supported, whereas the genera Cyathophorum and Dendrohypopterygium are unambiguously polyphyletic. Cyathophorum bulbosum and C. adiantum make up a lineage sister to the remainder of the family. A lineage comprising four monotypic genera (Arbusculohypopterygium, Canalohypopterygium, Catharomnion, and Dendrocyathophorum) is sister to Lopidium plus a heterogenous clade that includes Dendrohypopterygium, Hypopterygium, Cyathophorum hookerianum, and C. parvifolium. The later two species are transferred to Hypopterygium as H. hookerianum and H. parvifolium. The Hypopterygiaceae are distinguished from their sister family, the Hookeriaceae, by their anisophylly, and by a border of two or more differentiated cells on lateral leaves, although this character also occurs in some Hookeriaceae and has been lost at least twice in the Hypopterygiaceae. Intermediate cells in the axillary hairs arose early in the evolution of the family but are lacking in the two species of Cyathophorum that form a sister group to the remainder of the Hypopterygiaceae. © Copyright 2008 by the American Society of Plant Taxonomists.
Primer sequences are provided for amplification of 21 microsatellite- containing loci in Sphagnum. Although these primers were developed for species in Sphagnum section Subsecunda, they amplify microsatellite loci in most species that have been tested across the genus Sphagnum. Results are described from a survey of genetic variation in three species of Sphagnum collected in China: S. junghuhnianum in section Acutifolia, and S. palustre and S. imbricatum in section Sphagnum. Six and eight multilocus genotypes were detected within one population each of S. junghuhnianum and S. palustre, respectively. Four populations of S. imbricatum were sampled; they vary substantially in allele frequencies and in the amount of genetic diversity detected; overall, approximately 40% of the genetic variation sampled within S. imbricatum could be attributed to differentiation among populations. Microsatellite profiles indicate that S. palustre gametophytes are diploid whereas those of S. junghuhnianum and S. imbricatum are haploid. Copyright ©2008 by The American Bryological and Lichenological Society, Inc.
Populations and species of Sphagnum section Subsecunda are morphologically variable and it is often difficult from studying field-collected plants and herbarium specimens to delimit species. Allelic patterns at 20 microsatellite loci indicate that three distinguishable gene pools can be identified among plants from Australia and New Zealand. All three species are morphologically variable along a moisture gradient and this appears to be largely plastic, without genetic differentiation among species specific morphotypes. Sphagnum novozelandicum and S. comosum appear to have monoploid gametophytes, are closely related, and are endemic to Australia and New Zealand. The former usually occurs at or above water level and the latter is an aquatic plant with extensive morphological variation, ranging from simplex to branched morphotypes. Sphagnum fuscovinosum and S. simplex are synonyms of S. comosum. The third species is a highly disjunct population of the S. auriculatum/S. inundatum complex of Europe, which has not previously been reported for Australia and New Zealand. These plants appear to be polyploid and are genetically and morphologically distinct from both S. novo-zelandicum and S. comosum. All three species had duplicated loci amplified by one of the microsatellite primer pairs. Ten Sphagnum species are now reported for Australia and New Zealand, with three of these being endemic.
The systematics of Sphagnum section Sphagnum in New Zealand has been controversial. Two species are currently recognised in the New Zealand flora, S. cristatum and S. perichaetiale, but the presence of the widespread S. magellanicum has been debated. An analysis of 16 microsatellite loci shows that the gametophytes of Sphagnum perichaetiale appear to have one monoploid set of chromosomes (i.e., are haploid). Fixed heterozygosity at 10 loci indicates that S. cristatum is an alloploid. A red morphotype of S. cristatum, similar in macroappearance to S. magellanicum, is not genetically differentiated from the more common brown-green morphotypes of S. cristatum. Although analysis of the microsatellite data for S. cristatum showed most of the genetic variation to be within populations, significant variation did occur among populations within regions and also between regions. © The Royal Society of New Zealand 2008.
Aim: In contrast to angiosperms, bryophytes do not appear to have radiated in Macaronesia and the western Mediterranean. We evaluate if: (1) the apparent lack of radiation in bryophytes reflects our failure to recognize cryptic endemic species; (2) bryophytes are characterized by extremely low evolutionary rates; or (3) bryophytes have a high dispersal ability, which prevents genetic isolation. Location: Worldwide, with a special emphasis on Macaronesia and the western Mediterranean. Methods: Three chloroplast regions were sequenced from samples of the moss Grimmia montana from its entire distribution range. Network analyses, Fst and Nst statistics were used to describe and interpret the phylogeographical signal in the data. Results: Despite significant phylogeographical signal in the chloroplast genome, which demonstrates limits to gene flow at the continental scale, repeated sister group relationships observed among accessions from different geographical areas suggest recurrent colonization patterns. These observations are consistent with mounting evidence that intercontinental distributions exhibited by many bryophyte species result from long-distance dispersal rather than continental drift. Madeiran and western Mediterranean island haplotypes are either shared by, or closely related to, European and North American ones. Fst values between Madeira, western Mediterranean islands, North America and Europe are not significantly different from zero, and suggest that Madeira and the south-western Mediterranean are subject to strong transatlantic gene flow. By contrast, haplotypes found in the Canary Islands are shared or closely related to those of populations from south-western Europe or southern Africa. Main conclusions: Multiple origins and colonization events are not consistent with the hypothesis of a relictual origin of the Macaronesian moss flora. One possible reason for the failure of taxa that experienced multiple colonization events to radiate is niche pre-emption. We suggest that strong gene flow, coupled with the occupancy of all suitable niches, either by earlier conspecific colonizers or by other species, could be the mechanism preventing island radiation in G. montana and other cryptogams with high long-distance dispersal abilities. © 2007 The Authors.
We report the construction of a linkage map for the moss Ceratodon purpureus (n = 13), based on a cross between geographically distant populations, and provide the first experimental confirmation of maternal chloroplast inheritance in bryophytes. From a mapping population of 288 recombinant haploid gametophytes, genotyped at 121 polymorphic AFLP loci, three gene-based nuclear loci, one chloroplast marker, and sex, we resolved 15 linkage groups resulting in a map length of approximately 730 cM. We estimate that the map covers more than three-quarters of the C. purpureus genome. Approximately 35% of the loci were sex linked, not including those in recombining pseudoautosomal regions. Nearly 45% of the loci exhibited significant segregation distortion (alpha = 0.05). Several pairs of unlinked distorted loci showed significant deviations from multiplicative genotypic frequencies, suggesting that distortion arises from genetic interactions among loci. The distorted autosomal loci all exhibited an excess of the maternal allele, suggesting that these interactions may involve nuclear-cytoplasmic factors. The sex ratio of the progeny was significantly male biased, and the pattern of nonrandom associations among loci indicates that this results from interactions between the sex chromosomes. These results suggest that even in interpopulation crosses, multiple mechanisms act to influence segregation ratios.
Bryophytes comprise the root from which the green plant Tree-of-Life developed. Molecular methods have been applied to a range of evolutionary problems in bryophytes including phylogenetic relationships among the major lineages, delimination of families and genera, infraspecific geographic patterns and speciation. This symposium encompasses molecular phylogenetic analyses at various levels of organization. Presentations include overviews of where we stand on resolving relationships within the three divisions: Bryophyta (mosses), Marchantiophyta (liverworts) and Anthocerophyta (hornworts). Other presentations address the evolution of development in early land plants, the use of characters describing gene and genome structure in phylogenetic analyses and infra-specific, geographically-correlated molecular variation in bryophytes. Copyright ©2007 by the American Bryological and Lichenological Society, Inc.
To clarify long-standing disagreements about the taxonomic and phylogenetic status of Sphagnum macrophyllum and S. cribrosum, twenty-five samples of S. macrophyllum and twenty-four of S. cribrosum, including the rare wave-form morphotype, were sampled from ten states of the eastern United States. The data set included intensive sampling from three populations in North Carolina. Three anonymous genomic regions (rapdA, rapdB and rapdF) were sequenced for all the samples; two (nuclear) LEAFY introns (LEAFY1 and LEAFY2) and one chloroplast locus (trnG) were sequenced for all the samples excluding the twenty-two within-population North Carolina samples. The results showed that S. macrophyllum and S. cribrosum are reciprocally monophyletic with maximum parsimony bootstrap support and significant Bayesian posterior probabilities. Genetic analyses based on neutral coalescence models suggest that the simplest allopatric speciation model - the isolation model with no subsequent gene flow and constant population sizes - cannot be rejected. Nevertheless, some topological conflicts among loci suggest the possibility of limited interspecific hybridization. This study also showed that the morphologically distinctive wave-form is nested within S. cribrosum and wave-form samples from Singletary Lake make up a clade of nearly identical plants. Interestingly, S. macrophyllum and S. cribrosum are morphologically highly similar but are reciprocally monophyletic and highly differentiated, whereas the unique and morphologically divergent wave-form is genealogically derived from within normal S. cribrosum. © Copyright 2007 by the American Society of Plant Taxonomists.
Revolutionary new concepts of bryophyte relationships have emerged from molecular phylogenetic analyses conducted since the onset of the 21st century. For example, sequence data contradict the historical notion that isophylly in leafy liverworts is plesiomorphic and that simple thalloid liverworts are monophyletic. Also contrary to traditional views are the concepts that Leiosporoceros is genetically distinct from other hornworts and that Oedipodium is sister to the peristomate mosses. Substantial increases in ultrastructural and anatomical data likewise have provided new insights on interrelationships. Because of this recent deluge in evolutionary studies on bryophytes, it is an opportune time to co-examine contemporary morphological knowledge and novel molecular hypotheses. An understanding of bryophyte evolution and biology is essential to identify structural innovations that accompanied early land colonization and to illuminate the evolution of more complicated body plans in tracheophytes. In this review, we examine the progress that has been made since the 1999 International Botanical Congress in clarifying the evolutionary history of the three groups of bryophytes. The state of our knowledge on interrelationships is discussed, with poorly-known, genetically divergent taxa illustrated for each group. Our review of bryophyte evolution includes a reëvaluation of the evolution of sperm cells, sporogenesis, stomata, symbioses, conducting cells and chloroplast ultrastructure in hornworts. We explore the prospects for future discoveries and advances with an emphasis on fundamental evolutionary problems that remain and the challenges that must be met to resolve them. Copyright ©2007 by the American Bryological and Lichenological Society, Inc.
• Background and Aims: The recent assembly of the complete sequence of the plastid genome of the model taxon Physcomitrella patens (Funariaceae, Bryophyta) revealed that a 71-kb fragment, encompassing much of the large single copy region, is inverted. This inversion of 57% of the genome is the largest rearrangement detected in the plastid genomes of plants to date. Although initially considered diagnostic of Physcomitrella patens, the inversion was recently shown to characterize the plastid genome of two species from related genera within Funariaceae, but was lacking in another member of Funariidae. The phylogenetic significance of the inversion has remained ambiguous. • Methods: Exemplars of all families included in Funariidae were surveyed. DNA sequences spanning the inversion break ends were amplified, using primers that anneal to genes on either side of the putative end points of the inversion. Primer combinations were designed to yield a product for either the inverted or the non-inverted architecture. • Key Results: The survey reveals that exemplars of eight genera of Funariaceae, the sole species of Disceliaceae and three generic representatives of Encalyptales all share the 71-kb inversion in the large single copy of the plastid genome. By contrast, the plastid genome of Gigaspermaceae (Funariales) is characterized by a gene order congruent with that described for other mosses, liverworts and hornworts, and hence it does not possess this inversion. • Conclusions: The phylogenetic distribution of the inversion in the gene order supports a hypothesis only weakly supported by inferences from sequence data whereby Funariales are paraphyletic, with Funariaceae and Disceliaceae sharing a common ancestor with Encalyptales, and Gigaspermaceae sister to this combined clade. To reflect these relationships, Gigaspermaceae are excluded from Funariales and accommodated in their own order, Gigaspermales order nov., within Funariideae. © The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Sphagnum (peatmoss) dominates huge areas of the Northern Hemisphere and acts as a significant carbon sink on a global scale, yet little is known about the genetic structure of Sphagnum populations. We investigated genetic structure within a population of the common peatmoss Sphagnum fuscum, to assess local patterns of genetic diversity and the spatial extent of clones. One hundred seventeen shoots were sampled from five transects in Fuglmyra, central Norway, and sequenced for three anonymous DNA regions. Five neighbourhood patches were marked along each transect, and from each patch, five stems were sampled for molecular analyses. Seventeen haplotypes could be distinguished and two major groups of haplotypes differed by 12 mutational steps. The two major haplotype groups differed significantly in microhabitat association along the distance to groundwater table and the pH gradients, indicating microhabitat differentiation. The haplotypes within these groups were all genetically similar, differing by one or two mutations. The most common haplotype occurred in four transects separated by 250-m distance. Most of the molecular variation in the population was found among transects, and within patches. Large dominating clones within each transect resulted in low variation explained by the among-patch-within- transect component of spatial structure. Mutation appears to account for a larger proportion of the population variation than recombination. Within the population, vegetative growth and asexual reproduction from gametophyte fragments dominate as the main reproductive mode. © 2006 The Authors.
Habitat fragmentation increases the migration distances among remnant populations, and is predicted to play a significant role in altering both demographic and genetic processes. Nevertheless, few studies have evaluated the genetic consequences of habitat fragmentation in light of information about population dynamics in the same set of organisms. In a 10,000-km(2) experimentally fragmented landscape of rainforest reserves in central Amazonia, we examine patterns of genetic variation (amplified fragment length polymorphisms, AFLPs) in the epiphyllous (e.g. leaf-inhabiting) liverwort Radula flaccida Gott. Previous demographic work indicates that colonization rates in this species are significantly reduced in small forest reserves. We scored 113 polymorphic loci in 86 individuals representing five fragmented and five experimentally unmanipulated populations. Most of the variation (82%) in all populations was harboured at the smallest (400 m(2)) sampling unit. The mean ((+/-) SD) within-population genetic diversity (Nei's), of forest remnants (0.412 +/- 0.2) was indistinguishable from continuous (0.413 +/- 0.2) forests. Similarly, F(ST) was identical among small (1- and 10-ha) and large (> or = 100-ha) reserves (0.19 and 0.18, respectively), but linkage disequilibrium between pairs of loci was significantly elevated in fragmented populations relative to those in continuous forests. These results illustrate that inferences regarding the long-term viability of fragmented populations based on neutral marker data alone must be viewed with caution, and underscore the importance of jointly evaluating information on both genetic structure and demography. Second, multilocus analyses may be more sensitive to the effects of fragmentation in the short term, although the effects of increasing linkage disequilibrium on population viability remain uncertain.
Although habitat fragmentation is a major threat to global biodiversity, the demographic mechanisms underlying species loss from tropical forest remnants remain largely unexplored. In particular, no studies at the landscape scale have quantified fragmentation's impacts on colonization, extinction, and local population growth simultaneously. In central Amazonia, we conducted a multiyear demographic census of 292 populations of two leaf-inhabiting (i.e., epiphyllous) bryophyte species transplanted from continuous forest into a network of 10 study sites ranging from 1, 10, and 100 to > 10,000 ha in size. All populations experienced significantly positive local growth (lambda > 1) and a nearly constant per-generational extinction probability (15%). However, experimental leaf patches in reserves of > or = 100 ha experienced nearly double (48%) the colonization probability observed in small reserves (27%), suggesting that the proximate cause of epiphyll species loss in small fragments (
The moss genus Pohlia is most diverse in the Northern Hemisphere, but ten species occur in Australia, mostly in New South Wales and Tasmania. One species, P. clavaeformis, is endemic to Australia; P. tenuifolia is disjunct between Australia and South America; P. flexousa is widespread in southern Asia, and P. inflexa is high-latitude, circum-Antarctic. The remaining six species are more or less widespread in the Northern Hemisphere. Keys, descriptions, synonomy, and illustrations are provided. Pohlia mielichoferia and P. turgens are newly synonymized with P. clavaeformis; P. flexuosa and P. inflexa are newly reported from Australia. © Copyright 2006 by the American Society of Plant Taxonomists.
Species are the most common currency by which biodiversity is measured, but species are not equivalent in "biodiversity value" because of differences in phylogenetic history and current population processes. Morphologically defined species in Sphagnum section Acutifolia (Bryophyta) were compared with regard to how phylogenetically distinct each is from its sister species and how much nucleotide variation each encompasses. Comparisons were based on sequence variation at seven nuclear and chloroplast loci. Assignment of collections to morphospecies accounted for about 57-75% of the overall nucleotide variation at the seven loci, but morphospecies differed greatly in how much nucleotide diversity they encompass. In addition, morphospecies varied widely in their genetic distinctiveness, estimated as the length of the stem branch from the most recent common ancestor and numbers of differentially fixed and shared polymorphic nucleotides among taxa. Levels of molecular diversity within morphospecies were not correlated with their degree of isolation. Factors that affected the biodiversity value of species include age, mode of origin, demographic history, and reproductive biology.
The moss Ceratodon purpureus has long been used as a model system in plant development and physiology. However, the molecular population genetics of the species remains virtually unexplored. In this study, we used population genetic analyses of DNA sequence data from three unlinked loci (atpB-rbcL spacer, adk, and phy2) to examine biogeographical patterns in a global sample of this species. The three loci differed significantly in mutation frequency spectra and implied population structure. Pairs of haplotypes from single populations were frequently more divergent than haplotypes sampled from widely disjunct populations. In the atpB-rbcL spacer and adk samples, Australasian haplotypes were more closely related to Northern Hemisphere haplotypes than to haplotypes found in the equatorial regions. In contrast, the phy2 sample showed that the north and south temperate regions were genetically divergent, with the equatorial regions intermediate. Maximum-likelihood estimates (MLE) of the rates of migration between the two hemispheres were significantly different for the two nuclear genes. The frequency spectra of mutations indicated that differences in implied population structure among the three loci resulted from directional selection on the chloroplast genome and on the chromosomal segment containing adk. Collectively, these data suggest that long-distance migration within the Northern Hemisphere and Australasian regions is common (relative to the mutation rate) and that migration between these two regions, potentially via equatorial populations, is more frequent than migration among equatorial populations.
Gametophytes from six populations of the moss Philonotis fontana (Hedw.) Brid. were grown under two light and two water regimes in order to assess the effects of these environmental factors on gametophytic architecture and leaf and leaf-cell dimensions. Both light and water affected growth, but the light treatments had a greater effect, and on more characters, than did the water treatments. Significant population effects under common garden conditions point to genetic variation for several traits, and population x environmental treatment interactions demonstrated genetic variation for patterns of phenotypic plasticity, i.e. plants differed in their 'norms of reaction'. Variation among populations in leaf dimensions tended to have a strong genetic component (20-30% of the total variation), whereas cell dimensions showed relatively little genetic variation (<10% of the total). © British Bryological Society 2005.
The Sphagnum subsecundum complex includes a group of closely related, morphologically intergrading species in section Subsecunda. Nucleotide sequences from six genes (four nuclear and two chloroplast) were obtained from 74 populations representing all the putative species in this complex (S. denticulatum, S. inundatum, S. lescurii, S. subsecundum) to determine if the morphologically-defined taxa represent genetically distinct units. Sampling included populations from North America, Europe, and Asia. Parsimony analyses resolved two major groups of populations, one containing only North American plants (plus one from northern Russia) and the other containing all but two of the European samples, a few from North America, and one from Japan. Two of the four morphospecies occurred in both groups. Shimodaira-Hasegawa (SH) tests indicate that monophyly of S. inundatum, S. subsecundum, and S. lescurii can be rejected, whereas monophyly of S. denticulatum cannot be rejected with our data. Intragenic recombination was detected in both groups of populations, but was substantially higher in the "American" group. Because recombination calls into question the applicability of character-based phylogenetic methods, including parsimony, molecular similarity among populations was estimated using neighbor-joining. Neighbor-joining also resolved geographically correlated groups and corroborated the conclusion that morphologically defined species do not form genetically coherent groups. Groups oj populations more closely reflect geographic than morphological patterns. Copyright © 2005 by the American Bryological and Lichenological Society, Inc.
Isothecium myosuroides is an abundant and taxonomically problematic moss that occurs in Europe and on the west and east coasts of North America. It has sometimes been split into two taxa, I. myosuroides on the east coast of North America and in Europe, and I. stoloniferum on the west coast of North America. Isothecium stoloniferum has four distinct morphological types known as the ordinary, julaceous, coarse, and pinnate morphs. The degree to which the morphotypes are genetically distinct versus ecologically determined has been debated as has the distinction between I. stoloniferum and I. myosuroides, resulting in conflicting taxonomic treatments. This study uses phylogenetic analyses of the trnL-trnf and trnG regions of the chloroplast genome to examine relationships among the two species and four morphotypes. Molecular phylogenetic analyses reveal that there is some genetic basis to the morphs of I. stoloniferum, and that I. stoloniferum is paraphyletic. Accessions of I. myosuroides form a trans-Atlantic monophyletic group. The remaining samples form two distinct groups that each include samples of two morphotypes within I. stoloniferum. Populations of julaceous and ordinary morphotypes form a monophyletic group. Populations of coarse and pinnate morphotypes form an unresolved polytomy at the base of the clade that includes accessions of I. myosuroides. © Copyright 2005 by the American Society of Plant Taxonomists.
Pohlia robertsonii is newly described from central California. Plants with polysetous sporophytes immediately separate this species from all other members of the genus Pohlia in North America. Pohlia robertsonii is further characterized by firm, but not thickened leaf cells, paroicous inflorescences, long, narrowly cylindric capsules, and irregular peristomes in which the endostome segments equal or exceed the exostome teeth, and lack cilia. The peristomial formula is 4:2:2-4. Pohlia rabunbaldensis is described from the southern Appalachian Mountains of Georgia and North Carolina. The slender gametophytes bear single bud-like gemmae in upper leaf axils. The dull leaves that are somewhat shriveled on drying resemble those of P. annotina, but the large single gemmae with flexuose, broadly laminate leaf primordia resemble those of P. drummondii. The conspicuously decurrent leaves distinguish P. rabunbaldensis from both previously known species. Copyright © 2005 by the American Bryological and Lichenological Society, Inc.
A recent survey of arthrodontous mosses revealed that their chloroplast genome lacks the gene encoding the alpha subunit of the RNA polymerase (i.e., rpoA), and that at least in Physcomitrella patens the gene has been transferred to the nuclear genome. Subsequently the gene was recorded from the cytoplasmic genome in Takakia and Sphagnum. Here we extend the survey to representatives of all major lineages of mosses to determine when in the evolutionary history of the Bryophyta the loss took place. Amplifications using primers annealing to the flanking regions of the rpoA gene yield a product that contains the gene in Takakia, Sphagnum, Andreaea, Oedipodium, Polytrichaceae, and Buxbaumia. The gene is lacking in all arthrodontous mosses, including Diphyscium but also in both species of Tetraphis. Reconstruction of the transfer on the phylogeny of mosses suggests (a) that the rpoA gene was lost twice and (b) that the gene was lost after the divergence of Buxbaumiidae and prior to the divergence of Diphyscium from the remaining Bryopsida.
Taxonomic and molecular data were utilized to test the hypothesis that moss diversity is greatest near the equator. Species richness estimates from 86 taxonomic checklists representing global moss diversity do not support the hypothesis that, in general, mosses are more species-rich in the tropics than at higher latitudes. A significant latitudinal gradient was, however, detected for North, Central, and South American samples when analyzed alone. Taxonomic estimates of biodiversity patterns were compared to molecular estimates based on standing nucleotide diversity, and on phylogenetic diversity, the latter taking into account the historical information contained in a molecular phylogenetic tree for the mosses. Molecular estimates suggest that moss diversity is highest in the Southern Hemisphere and lowest in the Northern Hemisphere, with the tropics having an intermediate level. The differences, however, are slight, and analyses of molecular variance (AMOVA) indicate that there is virtually no generalized differentiation between major latitudinal zones. These results reflect the fact that virtually all moss lineages have representatives in all three latitudinal zones. At the nucleotide level, mosses best fit the pattern of "everything is everywhere".
Nucleotide sequences for six nuclear loci and one chloroplast region were used to reconstruct phylogenetic relationships in Sphagnum section Acutifolia. The combined data matrix, which includes 136 accessions (129 ingroup taxa and seven outgroups) and 5126 nucleotide sites, was analyzed using Bayesian inference. Most of the individual morphospecies commonly recognized in the section were represented by multiple populations, in some cases by up to 16 accessions from throughout the Northern Hemisphere. Results of the combined seven-locus analysis resolved many of the species as monophyletic, but the deeper nodes were generally without support. Separate analyses of single-locus data sets revealed significant conflicts, indicating gene flow among both closely and more distantly related species within the section. The sequence data allowed likely parentage to be identified for several species of hybrid origin, and identified individual accessions that appear to be genetic admixtures. Taxonomic conclusions that can be made from the analyses include: 1. Sphagnum wulfianum and S. aongstroemii should both be included in section Acutifolia, 2. S. subtile cannot be separated from S. capillifolium, and the two should be synonymized, 3. S. capillifolium and S. rubellum each contain a monophyletic core of populations and should be retained as separate species, but 4. S. rubellum cannot be separated from S. andersonianum and S. bartlettianum and the three should be merged, 5. S. tenerum is highly differentiated from S. capillifolium and should be treated as a separate species, 6. interspecific mixed ancestry is demonstrated for S. russowii (a likely allopolyploid), S. skyense, S. arcticum, and S. olafii. Interspecific recombination appears to be rather common in section Acutifolia, yet species, for the most part, maintain cohesiveness. © Copyright 2005 by the American Society of Plants Taxonomists.
Maximum likelihood analyses of DNA sequences from two chloroplast regions, trnL-trnF and atpB-rbcL, and the internal transcribed spacers of 18S-5.8S-26S rRNA gene array, were performed to resolve species relationships within the moss genus Hygroamblystegium. Constraining morphospecies to monophyly resulted in significantly less likely trees for H. tenax, but not for the other species. The lack of support for most clades and the partial incongruence among topologies necessitated the use of another independent, more variable region, namely the adenosine kinase gene (adk). Sequences for adk were polymorphic but were present as multiple copies within individuals, making parology a problem for phylogenetic analyses. Adk evolution was reconstructed using a reconciled gene tree approach in which duplications and losses were minimized in the context of an estimate of the species tree derived from the analysis of the cp and nrDNA sequence data. Additional resolution of the species tree was then obtained by searching for reconstructions that further reduced adk duplications and losses. All the traditionally recognized morphospecies appeared to be polyphyletic in the resulting tree. Together with previous data from different molecular markers, the results support the interpretation that Hygroamblystegium represents a recent radiation in which molecular and morphological evolution have been uncoupled.
Pohlia bolanderi (Lesq.) Broth. is reported for the first time for Europe from the south of Spain (Sierra Nevada range). A description from European material is provided and differences from closely related species, with which it has been confused, are discussed. It is also known from alpine regions in western North America, including British Columbia, Washington, Oregon, California, and Nevada.
The bryophytes comprise three phyla of embryophytes that are well established to occupy the first nodes among extant lineages in the land-plant tree of life. The three bryophyte groups (hornworts, liverworts, mosses) may not form a monophyletic clade, but they share life history features including dominant free-living gametophytes and matrotrophic monosporangiate sporophytes. Because of their unique vegetative and reproductive innovations and their critical position in embryophyte phylogeny, studies of bryophytes are crucial to understanding the evolution of land plant morphology and genomes. This review focuses on phylogenetic relationships within each of the three divisions of bryophytes and relates morphological diversity to new insights about those relationships. Most previous work has been on the mosses, but progress on understanding the phylogeny of hornworts and liverworts is advancing at a rapid pace. Multilocus multigenome studies have been successful at resolving deep relationships within the mosses and liverworts, whereas single-gene analyses have advanced understanding of hornwort evolution.
The moss family Splachnaceae is characterized by half of its members relying on insects for spore dispersal. These species grow on dung or other animal substrates. They produce small and aggregated spores, and their capsule is modified to attract coprophilous insects or carrion flies using olfactory and visual cues. Systematic concepts and implicit evolutionary inferences have relied much on variation in characters associated with the spore dispersal syndrome. Phylogenetic reconstructions based on sequence variation of two chloroplast loci (trnL-trnF region and the rps4 gene) suggest that most supraspecific taxa are poly- or paraphyletic. Transformations in morphological characters associated to the syndrome thus offer little if any phylogenetically informative signal. Brachymitrion is resolved in a nested position within Tayloria. A new combination, Tayloria immersa (Goffinet) Goffinet, Shaw & Cox is proposed for B. immersum. Only one of the five subgenera of Tayloria (subg. Orthodon) is potentially monophyletic. Voitia shares a common ancestor with Tetraplodon and is thus nested within the Splachnoideae. The affinities of Aplodon remain ambiguous. Reconstruction of shifts between wind and insect spore dispersal syndromes suggests that entomophily arose more than once and may have been followed by a reversal to the generalist strategy in two lineages.
Sphagnum macrophyllum, S. pylaesii, and S. cyclophyllum are morphologically atypical in the genus Sphagnum and their systematic placement has been a source of controversy. The first is generally classified in the mono-specific section Isocladus, and the second as section Hemitheca. Sphagnum cyclophyllum is classified in the section Subsecunda, but several authors have hypothesized a close relationship between all three species. Nucleotide sequences from eight nuclear and chloroplast loci were obtained to test hypotheses about relationships among these taxa. Phylogenetic analyses resolve these species (along with S. microcarpum, closely related to S. cyclophyllum) in a well-supported monophyletic group within the section Subsecunda. Sphagnum macrophyllum is sister to S. cyclophyllum, S. microcarpum, and S. pylaesii. Sphagnum cyclophyllum and S. microcarpum form a clade that is sister to S. pylaesii. Two mutually monophyletic groups of populations are resolved within S. pylaesii, one including the European populations and the other including populations from eastern North America and South America. The European populations are almost identical at the nucleotide sequence level whereas the American populations are genetically diverse. Short, delicate pseudopodia; exceptionally large opercula; and an absence or near absence of pseudostomata appear to be synapomorphies for the clade containing S. macrophyllum, S. microcarpum, S. cyclophyllum, and S. pylaesii.
The class Sphagnopsida (Bryophyta) includes two genera: Ambuchanania and Sphagnum. Ambuchanania contains just one rare species known from two Tasmanian localities, but Sphagnum comprises a speciose clade of mosses that dominates many wetland ecosystems, especially in the boreal zone of the Northern Hemisphere. Recent phylogenetic analyses have resolved well-supported clades within Sphagnum, but polarizing Sphagnum evolution has been problematic because the genus is so isolated that it is difficult to determine homologies between morphological and/or molecular traits within Sphagnum with those of any potential outgroup. DNA sequences from 16 genomic regions representing the mitochondrial, chloroplast, and nuclear genomes (ca. 16 kilobases) were obtained from 24 species of Sphagnum plus one species each from Takakia and Andreaea in order to resolve a rooted phylogeny. Two tropical species, S. sericeum and S. lapazense, were resolved as sister to the rest of the genus and are extremely divergent from all other sphagna. The main Sphagnum lineage consists of two clades; one includes the sections Sphagnum, Rigida, and Cuspidata, and the other includes Subsecunda, Acutifolia, and Squarrosa. The placement of section Subsecunda is weakly supported, but other nodes are strongly supported by maximum parsimony, maximum likelihood, and Bayesian analyses. In addition to homogeneous Bayesian analyses, heterogeneous models were employed to account for different patterns of nucleotide substitution among genomic regions.
Nuclear ribosomal 18S and internal transcribed spacer (ITS) sequence data were used to identify endophytic fungi cultured from six species of liverworts collected in Jamaica and North Carolina. Comparisons with other published fungal sequences and phylogenetic analyses yielded the following conclusions: (1) the endophytes belong to the ascomycete families Xylariaceae, Hypocreaceae, and Ophiostomataceae, and (2) liverwort endophytes in the genus Xylaria are closely related to each other and to endophytes isolated from angiosperms in China, Puerto Rico, and Europe. Liverwort endophytes are expected to be foragers or endophytic specialists, although little is known about the role of these fungi in symbioses. Features that may indicate a mutualistic role for these endophytes are discussed.
DNA sequence data from the nuclear ribosomal internal transcribed spacers (ITS) and the trnL-trnF chloroplast DNA regions were used to quantify geographical partitioning of global biodiversity in peatmosses (Sphagnum), and to compare patterns of molecular diversity with patterns of species richness. Molecular diversity was estimated for boreal, tropical, Neotropical, nonboreal (tropical plus Southern Hemisphere), Old World and New World partitions, based on a total of 436 accessions. Diversity was partitioned among geographical regions in terms of combined nuclear and chloroplast sequence data and separately for the ITS and trnL-trnF data sets. Levels of variation were estimated using phylogenetic diversity (PD), which incorporates branch lengths from a phylogenetic tree, and the number of polymorphic nucleotide sites. Estimates of species richness suggest that peatmoss diversity is higher in New World than Old World regions, and that the Neotropics constitute a "hotspot" of diversity. Molecular estimates, in contrast, indicate that peatmoss biodiversity is almost evenly divided between New and Old World regions, and that the Neotropics account for only 20-35% of global peatmoss diversity. In general, levels of tropical and boreal peatmoss molecular diversity were comparable. Two species, S. sericeum from the Old World tropics and S. lapazense from Bolivia, are remarkably divergent in nucleotide sequences from all other Sphagna and together account for almost 20% of all peatmoss diversity, although they are represented by only three of the 436 accessions (0.7%). These species clearly demonstrate the nonequivalence of species biodiversity value.
Pleurocarpous mosses, characterized by lateral female gametangia and highly branched, interwoven stems, comprise three orders and some 5000 species, or almost half of all moss diversity. Recent phylogenetic analyses resolve the Ptychomniales as sister to the Hypnales plus Hookeriales. Species richness is highly asymmetric with approximately 100 Ptychomniales, 750 Hookeriales, and 4400 Hypnales. Chloroplast DNA (cpDNA) sequences were obtained to compare partitioning of molecular diversity among the orders with estimates of species richness, and to test the hypothesis that either the Hookeriales or Hypnales underwent a period (or periods) of exceptionally rapid diversification. Levels of biodiversity were quantified using explicitly historical "phylogenetic diversity" and non-historical estimates of standing sequence diversity. Diversification rates were visualized using lineage-through-time (LTT) plots, and statistical tests of alternative diversification models were performed using the methods of Paradis (1997). The effects of incomplete sampling on the shape of LTT plots and performance of statistical tests were investigated using simulated phylogenies with incomplete sampling. Despite a much larger number of accepted species, the Hypnales contain lower levels of (cpDNA) biodiversity than their sister group, the Hookeriales, based on all molecular measures. Simulations confirm previous results that incomplete sampling yields diversification patterns that appear to reflect a decreasing rate through time, even when the true phylogenies were simulated with constant rates. Comparisons between simulated results and empirical data indicate that a constant rate of diversification cannot be rejected for the Hookeriales. The Hypnales, however, appear to have undergone a period of exceptionally rapid diversification for the earliest 20% of their history.
This study focused on three species that occur disjunctly between western North America and the Mediterranean region of southern Europe, northern Africa, and western Asia, forming the so-called Madrean-Tethyan distribution pattern. Quantitative morphological characters were measured in New and Old World plants to find any subtle phenotypic differentiation between the disjunct populations. Sequences from the nuclear ribosomal internal transcribed spacer region were obtained from the same populations to assess differentiation at the molecular level and to compare molecular diversity with patterns of morphological similarity among plants. Little or no morphological differentiation existed between New and Old World plants in any of the species, but internal transcribed spacer (ITS) sequences revealed some phylogeographic structure. Patterns of morphological similarity in all three species were incongruent with phylogeographic structure revealed by sequence data. New World populations were more variable than Old World populations at the molecular level in the three species. Despite some evidence for differentiation between disjunct plants, no plausible mutation rate would date the divergence at ≥20 million years ago (MYA), as implied by the Madrean-Tethyan hypothesis. Recent long-distance dispersal is a more likely explanation for intercontinental disjunctions in these species.
Many bryophyte species have distributions that span multiple continents. The hypotheses historically advanced to explain such distributions rely on either long-distance spore dispersal or slow rates of morphological evolution following ancient continental vicariance events. We use phylogenetic analyses of DNA sequence variation at three chloroplast loci (atpB-rbcL spacer, rps4 gene, and trnL intron and 3' spacer) to examine these two hypotheses in the trans-Antarctic moss Pyrrhobryum mnioides. We find: (1) reciprocal monophyly of Australasian and South American populations, indicating a lack of intercontinental dispersal; (2) shared haplotypes between Australia and New Zealand, suggesting recent or ongoing migration across the Tasman Sea; and (3) reciprocal monophyly among Patagonian and neotropical populations, suggesting no recent migration along the Andes. These results corroborate experimental work suggesting that spore features may be critical determinants of species range. We use the mid-Miocene development of the Atacama Desert, 14 million years ago, to calibrate a molecular clock for the tree. The age of the trans-Antarctic disjunction is estimated to be 80 million years ago, consistent with Gondwanan vicariance, making it among the most ancient documented cases of cryptic speciation. These data are in accord with niche conservatism, but whether the morphological stasis is a product of stabilizing selection or phylogenetic constraint is unknown.
ISSR (Inter-Simple Sequence Repeat) fingerprint data and nrITS sequences confirm the presence of Anacolia menziesii in Europe. The species is more variable genetically in North America than in Europe. The data show only minor differentiation between the North American and European populations of A. menziesii. Anacolia webbii is morphologically and genetically very similar to Anacolia menziesii, but can be separated from Anacolia menziesii with high confidence based on the ITS and ISSR data. Long distance dispersal is the most likely explanation for the disjunction of Anacolia menziesii between North America and Europe.
Restriction digest patterns from 18S-26S nuclear ribosomal DNA internal transcribed spacers (ITS) were employed to investigate delineation between the morphologically similar moss species Leucobryum glaucum, L. juniperoideum, and L. albidum. Discriminant analysis allowed assignment of specimens to haplotypes based on their morphological features and supported the recognition of L. glaucum and L. albidum. In contrast, L. albidum and L. juniperoideum both corresponded to the same haplotype. Many populations could be readily assigned to either L. glaucum or L. albidum by their morphological features. However, morphological variation between these two species was continuous and one of the ITS haplotypes could not be unambiguously characterized by its morphology. Genetically and morphologically identifiable specimens of L. albidum were sampled in Europe and North America, in contrast to the traditional interpretation of L. albidum as a North American endemic. Although L. albidum seems to have a more southern-Atlantic distribution pattern than L. glaucum, the two species occupy broadly overlapping geographic ranges and were sometimes found intermixed.
The Vittiaceae are a small family of aquatic mosses that are defined based on gametophytic traits whose interpretation has led to conflicting taxonomic arrangements. Phylogenetic analyses of two cpDNA regions, trnL-trnF and atpB-rbcL, indicate that Vittia is nested within the Amblystegiaceae s. str., suggesting that the family Vittiaceae should not be recognized. Platylomella lescurii appears nested within the Thuidiaceae/Leskeaceae. This suggests that the series of character states shared by Vittia and Platylomella, including a differentiated leaf border, short laminal cells, stiff stems, and a thick costa, are convergent features that arose independently in unrelated lineages of aquatic Hypnales. Within the Amblystegiaceae, phylogenetic analyses of the two cpDNA regions combined with ITS sequence data show that Hypnobartlettia, Vittia elimbata spec. nov., V. pachyloma, and V. salina, despite their strong morphological similarity to aquatic Amblystegium species, form a clade that is sister to the Drepanocladus/Pseudocalliergon complex. This combined clade is unresolved at a polytomy that includes Amblystegium serpens and a clade including all the other Amblystegium species. The occurrence of A. serpens outside the strongly supported clade including other Amblystegium species suggests that A. serpens may be better accommodated in a distinct genus. Amblystegium serpens is the type species of Amblystegium and thus retains the name. The other species are accommodated in their own genus, Hygroamblystegium, including H. fluviatile, H. humile comb. nov., H. noterophyllum, H. tenax, and H. varium.
To circumscribe the moss family Amblystegiaceae, we performed a broad-scale analysis of trnL-trnF spacer sequence data for 168 species of the Hypnales and 11 species of the Hookeriales and additional analyses of trnL-trnF and atpB-rbcL (chloroplast DNA), one nuclear region, the internal transcribed spacers of 18S-26S rDNA, and 68 morphological characters for a reduced data set of 54 species of Hypnales. The traditionally circumscribed Amblystegiaceae are polyphyletic and include the Amblystegiaceae s. str. and the Calliergonaceae fam. nov., plus several taxa closely related to other Hypnalean families. Generic relationships within the redefined Amblystegiaceae were investigated by analyzing data from the three DNA regions and morphology as used in the broader analysis. Reconstruction of morphological evolution was evaluated using maximum-parsimony and maximum-likelihood. Numerous independent character-state transitions implied by the phylogeny suggest that morphological characters that have traditionally been used to delineate the Amblystegiaceae are homoplastic. Sporophytic traits, which are generally given primacy over gametophytic traits in moss classification, are more labile than previously thought, and many characters that are related to sporophyte specializations are strongly correlated with habitat conditions. The evolution of several gametophyte features previously thought to be reliable for delineating the family are also strongly correlated with habitat. These observations help to explain the instability of the Amblystegiaceae in previous taxonomic and phylogenetic analyses based on morphology.
Leskeodon caducifolius is described from recent collections made at a single site in a cloud forest in southern Ecuador. The species is distinctive in its small, caducous leaves and elongate, porose exothecial cells.
The Dicranaceae have been classified as one of the largest, most heterogeneous families of the moss subclass Dicranidae. Circumscriptions of the family have varied, with some studies excluding selected subfamilies and recognizing them at the familial rank, whereas others have retained a broader familial concept. As well, classifications have varied in their generic circumscriptions of the subfamilies. Chloroplast DNA sequence data (trnL (UAA) - trnF (GAA) and rps4) were used to examine the monophyly of the family and phylogenetic relationships among the subfamilial and generic taxa. Special emphasis was given to subfamily Dicranoideae, with 18 of the 23 genera sampled. Seventy-four trnL-F and rps4 sequences formed a matrix of 1161 aligned base pairs (bp). Phylogenetic analyses using MP and ML criteria were based on 983 bp (333 parsimony informative) after ambiguous data were removed. Our results support the following inferences: 1) Dicranaceae as traditionally defined are polyphyletic; 2) subfamilies Campylopodioideae, Dicranelloideae, Rhabdoweisioideae, and Trematodontoideae are excluded from a robust monophyletic concept of the Dicranaceae; 3) subfamily Dicranoideae is polyphyletic unless 16 genera are excluded from the subfamily, seven of which are transferred to the Rhabdoweisiaceae; 3) subfamily Paraleucobryoideae is polyphyletic with Brothera resolved in the Leucobryaceae clade and Paraleucobryum nested within subfamily Dicranoideae; 4) Dicnemonaceae (including Mesotus) and Wardiaceae are nested within traditional members of the Dicranaceae; and 5) four clades - Dicranoideae, Mesotoideae, Dicranoloma group plus Wardia, and the Leucoloma group, form a robust monophyletic taxon, considered here as a restricted concept of Dicranaceae (sensu stricto). This circumscription excludes 18 genera that have previously been included in the Dicranaceae.
Phylogenetic analyses of infraspecific molecular data in relation to geographic and ecological information has come to be known as phylogeography. Bryophytes offer fertile material for such analyses, which can help clarify long standing biogeographic questions that were intractable before molecular data became available. In particular, molecular data can help distinguish between dispersal and fragmentation explanations for disjunct distributions that characterize many bryophytes at the specific as well as higher levels. Phylodemography is the application of molecular data and phylogenetic analyses to infer past changes in population size within species. Grounded in coalescence theory from population genetics, this new field could be fruitfully applied to bryophytes. Combining phylogeography and phylodemography yields a powerful strategy for elucidating evolutionary processes.
Many dung mosses (Splachnaceae) are characterized by insect-mediated spore dispersal. All of the entomophilous species are coprophilous, whereas anemophilous species are humicolous or epiphytic. The three species of the Voitioideae are coprophilous but are distinguished from other members of the family by sporangia that remain closed (cleistocarpous) and lack a peristome. Spores are released when the sporangial wall disintegrates. Phylogenetic analyses of nucleotide sequences of the trnL-trnF region and the rps4 locus (cpDNA) for 25 species of Splachnaceae suggest that this combination of characters arose twice within the Splachnaceae and that Voitia grandis is more closely related to species of Tayloria subgenus Tayloria rather to the other species of Voitia, which are nested within the genus Tetraplodon. Hence the new combination Tayloria grandis (Long) Goffinet & Shaw is made. Although the optimal trees were left unrooted, our results resolve the Voitioideae (i.e., the genus Voitia) as nested within the Splachnoideae. Tile phylogenetic significance of sporophytic characters within the family Splachnaceae is briefly discussed.
Results from a previous broad-scale analysis employing trnL-trnF sequence data for 168 Hypnalean and 11 Hookerialean taxa, and an analysis employing two chloroplast regions, trnL-trnF and atpB-rbcL, one nuclear region, the internal transcribed spacers of 18S-26S rDNA, plus 68 morphological characters for a reduced data set of 54 Hypnalean taxa, were used to circumscribe Amblystegiaceae. The analyses provided two well-supported main clades including taxa traditionally included in Amblystegiaceae s.l. and recognized as Amblystegiaceae s.str. [Anacamptodon, Amblystegium, Campyliadelphus, Campylium, Cratoneuron, Cratoneuropsis, Drepanocladus s.str., Gradsteinia, Hygrohypnum s.str. (including the type species, H. luridum, but excluding a number of other species previously accommodated in the genus), Hypnobartlettia, Leptodictyum, Palustriella, Pseudo-calliergon, and Serpoleskea] and Calliergonaceae stat. nov. (Calliergon, Hamatocaulis, Loeskypnum, Straminergon, and Warnstorfia). Scorpidium and "Hygrohypnum" ochraceum were closely related to Calliergonaceae but were not included in the family because of the lack of support. All these genera but Anacamptodon have previously been included in Amblystegiaceae s.l. The sporophytic features of Anacamptodon, which contrast with those of all the other members of Amblystegiaceae, are interpreted as adaptations to an epiphytic habitat and suggest, together with other recent taxonomic works in Hookeriales, that characters related to sporophytic specializations are among the most homoplastic. Several other taxa (Calliergonella, Campylophyllum, Conardia, Donrichardsia, "Hygrohypnum" smithii, Platydictya, Sanionia), previously included in Amblystegiaceae s.l., appeared more closely related to other Hypnalean families. Recircumscribed Amblystegiaceae, and several clades within the family, have no identifiable morphological synapomorphies. A new system of classification for recircumscribed Amblystegiaceae, including morphological delimitation of presented clades based on maximum likelihood reconstruction of ancestral character states, is proposed and appropriate nomenclatural changes made.
The simple (but elegant) series of experiments performed by McHaffie et al. (see pp. 491-500 in this issue) - involving studies of segregation from field-collected sporophytes, sporophytic progeny of selfed gametophytes, and the morphology of sporophytes from reciprocal crosses - conclusively demonstrates the genetic basis of the intervarietal morphological differences. These differences are further conditioned by one gene and two alleles, with the 'distentifolium allele' (AD) dominant over the 'flexile allele' (AF). Did the authors also achieve their goal of determining those factors that might help explain how flexile is maintained within populations? The issue is complex. Gametophytes of the flexile type seem to have a consistent growth advantage, and it might be that this translates into a reproductive advantage. In the sporophyte generation, pleiotropic effects of the AF allele appear to confer an advantage in terms of frond number and fertility to the flexile form at high nutrient concentrations, whereas at the same high nutrient levels the AD (distentifolium) allele is associated with larger fronds. From this, the authors hypothesize 'antagonistic pleiotropy' for the maintenance of the AF allele in Scottish populations of A. distentifolium. Whether or not this is correct, they have provided new information about this fern that has implications for both conservation and basic evolutionary biology.
The Amblystegiaceae include pleurocarpous mosses typical of moist, wet, or aquatic habitats. Sporophytes are uniform, and genera are distinguished by the habit, arrangement, and anatomy of leaves, leaf cell shape, and costal structure. Generic limits are controversial. Species have been shifted from genus to genus, sometimes in or out of other related families. Nucleotide sequences from the Internal Transcribed Spacer region of nuclear ribosomal DNA repeat from 39 accessions were analyzed to test monophyly of the genera Amblystegium, Campylium, and Drepanocladus. Reconstructions constrained to support monophyly of each genus were significantly less parsimonious and less likely than from unconstrained searches. ITS sequences support previous suggestions based on morphology that Campylophyllum halleri is not closely related to Campylium stellatum or Campyliadelphus chrysophyllus. Our results also support previous treatments that divide Drepanocladus into two or more segregate genera. Leptodictyum riparium appears more closely related to Campylium stellatum and Campyliadelphus chrysophyllus than to Amblystegium species. Some, but not all, populations of A. humile, Hygroamblystegium tenax, H. fluviatile, and H. varium form a strongly supported clade.
Phylogenetic analyses of nucleotide and amino acid sequences of the chloroplast protein coding gene rps4 were performed for 225 species of mosses, representing 84 % of families recognized by Vitt (1984. In: Schuster RM, ed. New manual of bryology, vol 2. Nichinan: Hattori Botanical Laboratory), under the criterion of maximum parsimony with Takakia and Sphagnum as outgroups. Most parsimonious topologies converge to a scenario wherein the Andreaeidae are monophyletic and sister to the Bryidae (peristomate mosses), the Nematodonteae and the Buxbaumiaceae form a monophyletic lineage, the Diphysciaceae are sister to the Arthrodonteae and, within the latter, the Funarineae-Encalyptineae-Timmiaceae-Haplolepideae compose a monophyletic clade sister to remaining diplolepideous mosses. This hypothesis suggests that early in the evolution of the Arthrodonteae, two major lineages diverged, with opposite and alternate peristomes, respectively. Bootstrap support for the deep dichotomies is poor or lacking but increases when protein translations of rps4 sequences are included in the analysis. Several novel systematic hypotheses are raised, including (a) a diplolepideous rather than haplolepideous origin of the Pleurophascaceae; (b) an affinity of the Catascopiaceae with the Funariineae rather than the Bryineae; and (c) a close relationship of the Calomniaceae and Mitteniaceae to the Rhizgoniaceae. The advantages and disadvantages of a single gene phylogeny are discussed with respect to the identification of polyphyletic familial or suprafamilial taxa. © 2001 Annals of Botany Company.
Nuclear ribosomal DNA (internal transcribed spacer region) and chloroplast DNA (trnL-trnF region) were sequenced from 40 samples representing all three genera (Brachelyma, Dichelyma, and Fontinalis) and 18 species of the aquatic moss family, Fontinalaceae. Phylogenetic reconstructions recovered from separate and combined analyses were used to test the hypotheses that Fontinalis and Dichelyma are monophyletic (Brachelyma is monotypic), that groups of species within Fontinalis based on leaf morphology (keeled, concave, plane) form monophyletic groups, and that species delineation based on morphological characters within Fontinalis are congruent with nr- and cpDNA gene trees. Using Brachelyma subulata to root the tree, both Dichelyma and Fontinalis are monophyletic and patristically divergent (each united by >15 synapomorphic mutations). Groups of species within Fontinalis defined by leaf morphology are polyphyletic and it is clear that leaf morphology is labile in the genus. As defined morphologically, species of Fontinalis are nonmonophyletic for both nr- and cpDNA sequences and populations of some morphological taxa are separated in widely divergent clades. Molecular evidence suggests that at least some morphospecies are artificial, defined by convergent leaf forms. The weight of the evidence indicates that F. antipyretica is positively paraphyletic, with European populations more closely related to (i.e., share a more recent common ancestor with) European endemic species than to North American populations that are morphologically conspecific. North American populations are more closely related to North American endemic species.
Nucleotide sequence variation in the ITS1-5.8S-ITS2 region of nuclear ribosomal DNA (nrDNA) from 70 populations of Mielichhoferia elongata and M. mielichhoferiana, plus two outgroup species, was analysed using maximum parsimony and maximum likelihood methods. High levels of nucleotide substitution and numerous insertion-deletion events were detected within and between the two species. M. elongata is monophyletic with regard to nrDNA variation, but M. mielichhoferiana is paraphyletic. (M. elongata is nested within it.) A clade within M. mielichhoferiana provides evidence of vicariance, with North American and Scandinavian sister groups of populations. Two major clades are resolved in M. elongata by sequence data that are completely congruent with previous isozyme work. One clade includes populations from both North America and Europe whereas the other is strictly North American. These two clades, resolved by multiple independent loci, clearly represent cryptic species within the morphologically uniform M. elongata. Certain geographical areas, most notably southwestern Colorado in Ouray and San Juan Counties, harbour diverse populations of M. elongata with distinct phylogenetic and phylogeographical histories. Morphologically indistinguishable but phylogenetically distant populations were detected a few metres apart at one site. In contrast, all populations collected over hundreds of kilometres in California belong to a single clade. Arctic North American populations belong to a clade that includes disjunct populations in Alaska, northern Ellesmere Island, and the northeastern USA, but not subarctic Swedish populations, which are more closely related to plants from the Rocky Mountains. Morphological uniformity belies complex infraspecific phylogenetic patterns within M. elongata and M. mielichhoferiana.
Cleistocarpous mosses, those lacking a differentiated operculum and having the capsule dehisce irregularly, are generally thought to have evolved via reduction from stegocarpous ancestors. Bruchia (Bruchiaceae), a cleistocarpous genus of approximately 15 species, shares gametophytic similarities with the genus Trematodon, which has a functional annulus and dehiscent capsule. The sequence of cell divisions characterizing the sporophyte of Bruchia flexuosa shows that development is typically haplolepideous up to the stage in which the peristomial formula is 4:2:2. Whereas other haplolepideous species, including Trematodon longicollis, complete development with a 4:2:3 peristomial formula, the last set of anticlinal divisions in the Inner Peristomial Layer do not occur in B. flexuosa, which therefore appears to mature at what is an immature stage in related stegocarpous taxa. This pattern of development is consistent with an origin of the cleistocarpous capsules of Bruchia through paedomorphosis from a Trematodon-like (haplopideous) ancestor.
The authors define a new feature of a circadian rhythm, the reset zone, and point out its usefulness for predictions concerning oscillator behavior. The reset zone measures the responses of a circadian system to resetting pulses. It can be easily determined from a phase transition curve (PTC), which is simply a phase response curve (PRC) replotted as new phase versus old phase (Winfree's format). The reset zone is the range of new phases seen in such a plot and has two potentially useful characteristics: its size and its midpoint. A series of experiments with Neurospora involving temperature pulses indicated that the size of the reset zone changed in a nonlinear way in response to both the duration of 40°C pulses and to the magnitude of temperature change for 3-h pulses. Other existing data are replotted to show how the reset zone size varies with growth temperature and with the period of different clock mutants. Employing exclusively reset zone data within the framework of a limit cycle displacement model, an equation is formulated that predicts the relative changes in the values of state variables of the oscillator for changes in any given environmental condition, such as temperature. Examples are also drawn from other organisms, such as hamsters, Gonyalaux, Kalanchoe, and Drosophila, illustrating the usefulness of the reset zone measurement. It can be used as a numerical scale for assessing the strength of a pulse, for comparing the relative effects of a given pulse applied to different organisms or mutants, for determining the directionality of the changes in state variables produced by various types of pulses, and possibly for measuring clock amplitude.
Phylogenetic analyses of nuclear and chloroplast DNA sequences resolve four major clades within the peatmosses, and these lineages correspond to sections that have traditionally been recognized based on morphology. The sectional placement of most species is unambiguous, but four taxa combine the nuclear sequences of one section with the chloroplast sequences of another. A hypothesis of past reticulate evolution is favored over lineage sorting to account for this incongruence, because single genome analyses (nuclear vs. chloroplast) indicate that the species are derived within their respective sections. Sphagnum mendocinum, from the Pacific coast of North America, has the nuclear DNA of section Subsecunda, but the chloroplast DNA of section Cuspidata. Sphagnum cuculliforme, from Ecuador, has the nuclear sequences of section Subsecunda, but the chloroplast sequences of section Sphagnum. Sphagnum falcatulum and S. ehyalinum, both from temperate Southern Hemisphere, have the nuclear sequences of section Cuspidata, but the chloroplast sequences of section Subsecunda. While morphological evidence alone would not be sufficient to hypothesize past reticulations, at least three of the four species are atypical and ambiguous with regard to sectional placement. Sphagnum mendocinum is morphologically intermediate between the Subsecunda and Cuspidata, S. cuculliforme has previously been classified in its own monotypic section because of a unique combination of morphological characters, and S. ehyalinum is highly unusual because of a near absence of differentiated chlorophyllose and hyaline cells in the branch leaves. S. ehyalinum is described as new in this paper. Sphagnum falcatulum is morphologically typical of the section Cuspidata, to which it appears to belong based on nuclear DNA sequences. These inferences of reticulation between widely divergent taxa add to growing evidence of hybridization in the peatmosses.
Most reconstructions of basal land plant relationships derived from morphological or molecular data suggest that the Sphagnopsida form a critical clade at or near the base of the mosses (Bryophyta s.s.). The Sphagnopsida include two orders: Sphagnales and Ambuchananiales, each with one family. The Ambuchananiaceae is monotypic, with A. leucobryoides of Tasmania. Nucleotide sequences from five genomic regions, two from the nuclear genome (ITS and 26S nuclear ribosomal DNA) and three from the chloroplast genome (psbT, rpl16, trnL) were subjected to cladistic analyses in order to assess 1) the relationship between Ambuchanania and Sphagnum, 2) the polarity of evolutionary change in Sphagnum (i.e., infer a root for the infrageneric phylogeny), 3) monophyly of the four large sections of Sphagnum (Acutifolia, Cuspidata, Sphagnum, and Subsecunda) and 4) phylogenetic relationships of the smaller or monotypic sections. Ambuchanania is resolved as the sister group to Sphagnum and is not nested within the latter as a highly derived species. Polarity of evolutionary change in Sphagnum is ambiguous; alternative hypotheses suggested by molecular data place either the sect. Subsecunda or the sect. Sphagnum as sister to all other species. The four large sections of Sphagnum are each monophyletic if circumscribed to include species traditionally placed in monotypic sections. Sphagnum macrophyllum (sect. Isocladus) is nested within the Subsecunda. Sphagnum pylaesii (sect. Hemitheca) is nested within the Cuspidata and is closely related to S. tenellum (sect. Mollusca). Sphagnum wulfianum (sect. Polyclada) is nested within the Acutifolia, closely related to S. fimbriatum and S. girgensohnii. Sphagnum aongstroemii (sect. Insulosa) is either nested within the Acutifolia, or is sister to other species of Acutifolia. Molecular evidence supports a sister group relationship between the sections Rigida and Sphagnum, and between the sections Squarrosa and Acutifolia. Molecular data suggest that phylogenetic structure in Sphagnum can be accommodated by four large sections without segregating morphologically distinctive taxa into smaller sections, as is traditionally done. A revised classification is proposed in which the genus is divided into four sections: Acutifolia, Cuspidata, Sphagnum, and Subsecunda.
A new moss species, Schizymenium shevockii, is described from Fresno County, California. Schizylnenium shevockii is distinguished from North American species of Mielichhoferia by a single endostomial peristome, and from Mexican species of Schizymenium by dioicous sexuality, poorly developed endostome segments, and the complete absence of exostome teeth. The new species can also be distinguished from S. pontevedrensis (the only European species of that genus), Mielichhoferia mielichhoferiana, and Mielichhoferia elongata by the presence of 38 and 29 nucleotide (nt) deletions in the ITS1 region of nuclear ribosomal DNA, and a nine nt insertion in the ITS2 region. Four additional insertions and/or deletions distinguish S. shevockii from M. elongata and/or M. mielichhoferiana. Moreover, Mielichhoferia elongata and M. mielichhoferiana share 34 nucleotide substitutions that distinguish them (as a monophyletic group) from S. shevockii and S. pontevedrensis. A survey of California populations using primers designed to take advantage of molecular differences between S. shevockii and morphologically similar but sterile plants of Mielichhoferia elongata revealed plants of S. shevockii at three sites. At one such site, S. shevockii was sympatric with M. elongata. All samples of S. shevockii had identical ITS sequences.
The ordinal classification of pleurocarpous mosses rests on characters such as branching mode and architecture of the peristome teeth that line the mouth of the capsule. The Leucodontales comprise mainly epiphytic taxa, characterized by sympodial branching and reduced peristomes, whereas the Hypnales are primarily terricolous and monopodially branching. The third order, the Hookeriales, is defined by a unique architecture of the endostome. We sampled 78 exemplar taxa representing most families of these orders and sequenced two chloroplast loci, the trnL-trnF region and the rps4 gene, to test the monophyly and relationships of these orders of pleurocarpous mosses. Estimates of levels of saturation suggest that the trnL-trnF spacer and the third codon position of the rps4 gene have reached saturation, in at least the transitions. Analyses of the combined data set were performed under three optimality criteria with different sets of assumptions, such as excluding hypervariable positions, downweighting the most likely transformations, and indirect weighting of rps4 codon positions by including amino acid translations. Multiple parallelism in nonsynonymous mutations led to little or no improvement in various indices upon inclusion of amino acid sequences. Trees obtained under likelihood were significantly better under likelihood than the trees derived from the same matrix under parsimony. Our phylogenetic analyses suggest that (1) the pleurocarpous mosses, with the exception of the Cyrtopodaceae, form a monophyletic group which is here given formal recognition as the Hypnidae; (2) the Leucodontales are at least paraphyletic; and (3) the Hypnales form, with most members of the Leucodontalean grade, a monophyletic group sister to a Hookerialean lineage. The Hypopterygiaceae, Hookeriales, and a clade composed of Neorutenbergia, Pseudocryphaea, and Trachyloma likely represent a basal clade or grade within the Hypnidae. These results suggest that mode of branching and reduced peristomes are homoplastic at the ordinal level in pleurocarpous mosses, (C) 2000 Academic Press.
The diplolepideous-alternate peristome, when most highly developed, has endostome segments attached to a basal membrane and positioned alternate to the outer exostome teeth, with cilia often present between the segments. This peristome type defines the Bryidae (sensu Vitt et al. 1998), which includes four orders: the Bryales, Leucodontales, Hypnales, and Hookeriales, of which the latter three are mainly pleurocarpous in their growth form. Chloroplast (rbcL, rps4, and trnL-trnF) and nuclear (18S rRNA) gene sequences have been analyzed using the parsimony optimality criterion to elucidate relationships among the Bryidae. The analyses strongly support the paraphyly of the Bryidae, with the Splachnidae, and possibly the Orthotrichidae, having arisen from ancestors within the Bryidae. The Leucodontales, Hypnales, and Hookeriales form a monophyletic group, as do the pleurocarpous members of the Bryidae. However, the two pleurocarpous clades are not resolved as sister groups, although their non-monophyly is not supported by the bootstrap. The phylogenetic hypothesis provides a context in which to infer evolutionary transitions in some key morphological characters relating to the peristome and the transition from the acrocarpous to pleurocarpous growth forms.
Classification of families of hypnobryalean mosses into the Hypnales, Leucodontales, and Hoolceriales has been taxonomically difficult. Several researchers have sequenced different genes for independent phylogenetic studies of these three pleurocarp groups. Our goal is to summarize available molecular data and compile the largest data set to infer phylogenetic relationships among families as basis for classification at ordinal level. Sequences of rbcL, trnL-F, and rps4 loci for 38 exemplars of most families of Hypnales, Leucodontales, and Hookeriales were analyzed to evaluate whether or not each of the three orders is monophyletic. Cladistic analyses of combined sequences, using five taxa in the Bryales as outgroups, reveal a robust clade (decay > 5) including all hypnobryalean pleurocarps. Within this group, one clade (decay = 2) includes only taxa of the Hookeriales, and is sister to a large monophyletic group (Hypnales sensu lato) containing all other taxa (decay = 2) previously in the Leucodontales and Hypnales. These relationships suggest that the ordinal level taxonomy needs to be reconsidered since major lineages detected do not correspond to the traditional Leucodontales or Hypnales. These two orders are not supported by any molecular evidence from rbcL, trnL-F, or rps4, either analyzed singly or in different combinations. Additionally, present results indicate the need for changes to the current system of three suborders of Hypnales and four of the Leucodontales. Phylogenetic reconstructions based on molecular data emphasize the need for a re-examination of the taxonomic relevance of morphological characters and corroborate previous interpretations of sporophytic morphological similarities as multiple transitions to similar solutions to epiphytism among the pleurocarps.
Mosses with haplolepideous peristomes form a major lineage within the arthrodontous taxa, the Dicranidae. Relationships among lineages within the Dicranidae are explored using three cpDNA regions: rbcL, rps4, and the region spanning trnL(UAA)- trnF(GAA). Maximum parsimony analyses of combined data sets support robust clades that correspond to traditionally recognized families. Phylogenetic relationships of 71 exemplar taxa rooted with five outgroup taxa identify 13 major clades within the Dicranidae. Predominantly the monophyly of these groups is strongly supported, although relationships among the clades are ambiguous. The phylogenetic implications of the current taxon sampling include 1) the Dicranidae are monophyletic, 2) the Pottiales are polyphyletic with the Calymperaceae and Octoblepharaceae cladistically distant from the Pottiaceae, and these two former families should be transferred to the Dicranales, 3) the Dicranales are polyphyletic, with Ditrichaceae and Rhabdoweisiaceae more closely related to the Pottiaceae than other members of the Dicranales, 4) the Fissidentaceae are nested within the Dicranales, 5) the Rhachitheciaceae and Erpodiaceae are nested within the Dicranidae and sister to the Pottiaceae, 6) Amphidium is sister to the pottiaceous clade, 7) the Seligeriaceae form a well supported sister relationship to the Grimmiales, and 8) Scouleria aquatica, Bryoxiphium norvegicum, Ditrichum flexicaule, and Timmiella crassinervis appear to form basal lineages within the Dicranidae.
As a result of a project using two chloroplast loci, the trnL-trnF region and the rps4 gene, to test the monophyly of pleurocarpous mosses as a group and the traditional three orders contained in it, several novel generic alliances were revealed. Of particular interest are the inclusion of the Ptychomniaceae and Garovagliaceae in the Hookeriales, as well as generic inclusions in the Anomodontaceae, Brachytheciaceae, Amblystegiaceae sensu lato, and Sematophyllaceae.
The life cycles of mosses and other bryophytes are unique among land plants in that the haploid gametophyte stage is free-living and the diploid sporophyte stage is ephemeral and completes its development attached to the maternal gametophyte. Despite predictions that populations of haploids might contain low levels of genetic variation, moss populations are characterized by substantial variation at isozyme loci. The extent to which this is indicative of ecologically important life history variation is, however, largely unknown. Gametophyte plants from two populations of the moss Ceratodon purpureus were grown from single-spore isolates in order to assess variation in growth rates, biomass accumulation, and reproductive output. The data were analyzed using a nested analysis of variance, with haploid sib families (gametophytes derived from the same sporophyte) nested within populations. High levels of life history variation were observed within both populations, and the populations differed significantly in both growth and reproductive characteristics. Overall gametophytic sex ratios did not depart significantly from 1:1 within either population, but there was significant variation among families in both populations for progeny sex ratio. Some families produced predominantly male gametophytes, while others yielded predominantly females. Because C. purpureus has a chromosomal mechanism of sex determination, these observations suggest differential (but unpredictable) germination of male and female spores. Life history observations showed that male and female gametophytes are dimorphic in size, maturation rates, and reproductive output.
Two species of lichens, Vezdaea leprosa (P. James) Vezda and Steinia geophana (Nyl.) B. Stein are here reported as new for North America based on collections from Durham and Orange Counties, North Carolina (U.S.A.). Both species occur frequently in the area on zinc-contaminated soils below galvanized electricity pylons. The species were not found in areas between pylons, suggesting a central role for elevated substrate zinc levels in determining the local distribution of these species. This inference is consistent with the ecology of these species in Britain and Europe.
The moss genus Pohlia includes species with bisexual gametophytes, unisexual gametophytes and no specialized asexual propagules, and unisexual with specialized asexual 'gemmae.' A group of Northern Hemisphere species characterized by having axillary gemmae are very similar in other gametophytic characters, and virtually identical in sporophyte morphology, in contrast to most other species of Pohlia that differ in both gametophytic and sporophytic features. This study tested the hypothesis that gemmiferous taxa form a complex of 'microspecies' that are less distinct genetically than are comparable sexual species. Fourteen putative isozyme loci were screened in 50 populations representing 11 species (7 gemmiferous and 4 nongemmiferous). The seven gemmiferous species are less distinct from one another (mean I = 0.8999) than are the four species that do not form gemmae (mean I = 0.7530). Species lacking gemmae have higher total infraspecific gene diversity (mean H(T) = 0.254) than gemmiferous species (mean H(T) = 0.138).
The classification of the Bryopsida is based to a large extent on the architecture of the peristome teeth. Among diplolepideous mosses, three peristome-types have been recognized. The development of the amphithecium in taxa characterized by an Orthotrichum-type peristome is described here, thereby completing our survey of the ontogeny of all three diplolepideous peristome types. Patterns of early divisions leading to a three-layered amphithecium in Schlotheimia rugifolia, Ulota crispa, and U. hutchinsiae are identical to all other arthrodontous mosses that have been studied. The subsequent anticlinal divisions occurring in the eight celled Inner Peristomial Layer are clearly asymmetric. Lack of alignment of adjacent anticlinal IPL and Primary Peristomial Layer walls is further accentuated by post-divisural lateral displacement of the IPL walls due to swelling of the PPL cells. This development of the amphithecial layers yielding a 4:2:4 pattern in the Orthotrichaceae is identical to that described for the Bryum-type peristome. The asymmetry of the critical late stage division in the IPL is considered homologous between these types. Based on recent phylogenetic hypotheses for the Bryopsida, we propose to extend this homology assumption to the Haplolepideae, the Diphysciales, and the Tetraphidales, suggesting that the asymmetric division is likely plesiomorphic within the Arthrodonteae. Whether the peristome of the Orthotrichaceae represents a primitive bryalean peristome, or whether it arose through reduction of a bryoid-type remains to be addressed further.
Mielichhoferia paroica Shaw ang Allen is described from Costa Rica. The plants are very small, paroicous, and have a double peristome that consists of 16 long, papillose exostome teeth and a rudimentary basal membrane that barely reaches above the capsule rim. Mielichhoferia paroica is the only known species of Mielichhoferia that is not dioicous. Brachymenium gemmifarum Shaw and Buck is described from Reunion. Plants of this species are extremely slender, and have red capsules with a double peristome consisting of long exostome teeth and a high endostomial membrane but no well-defined segments. It differs from all other species of Brachymenium in having axillary, obconic gemmae.
Leucobryum glaucum and L. albidum are generally distinguished by quantitative differences in plant height, leaf length, and transverse sectional leaf anatomy. Although extremely small plants can be readily identified as L. albidum, and large plants can be confidently assigned to L. glaucum, intermediate forms are common and many identifications are arbitrary. We amplified approximately 815 bp of the nuclear ribosomal DNA ITS from plants varying in size, and cut the products with three restriction endonucleases (Hhal, Hinfl, and Taql). Two DNA haplotypes were detected in a sample of 23 plants growing at a forested site in Durham, North Carolina. All plants with leaves 5.0 mm in length or shorter had one haplotype, and all plants with leaves longer than 5.0 mm had the other haplotype. Our results support the interpretation that L. albidum (small plants) is genetically discontinuous with L. glaucum (large plants), at least in the limited area from which we sampled.
Epistatic genetic variance for quantitative traits may play an important role in evolution, but detecting epistasis in diploid organisms is difficult and requires complex breeding programs and very large sample sizes. We develop a model for detecting epistasis in organisms with a free-living haploid stage in their life cycles. We show that epistasis is indicated by greater variance among families of haploid progeny derived from individual diploids than among clonally replicated haploid sibs from the same sporophyte. Simulations show that the power to detect epistasis is linearly related to the number of sporophytes and the number of haploids per sporophyte in the dataset. We illustrate the model with data from growth variation among gametophytes of the moss, Ceratodon purpureus. The experiment failed to detect epistatic variance for biomass production, although there was evidence of additive variance.
Substrate analyses of 41 samples for Mielichhoferia elongata and three each for M. mielichhoferiana and M. macrocarpa were conducted to determine if high copper concentrations are a constant feature of their habitats. Soil analyses showed that relatively few populations of M. elongata grew on soil with significant copper enrichment. Many sites, however, contained higher than normal levels of aluminium, iron, or manganese, or various combinations of these metals. M. elongata was neither tolerant of high copper supplied in nutrient media, nor did it require excess copper for vigorous growth. Scopelophila cataractae, in contrast, grew best on media containing 9 ppm copper. -From Authors
Scopelophila cataractae, one of the so-called "copper mosses", has a broad geographic distribution that includes North, Central, and South America, Europe, and Asia, but is rare throughout its range. A genetic analysis of 32 populations from the United States, Europe, and Asia based on 15 putative allozyme loci indicates that levels of genetic diversity vary among geographic regions. Six European populations are fixed for the same alleles at all 15 loci, consistent with the hypothesis that S. cataractae is a recent immigrant in that region. The species is more diverse in the U.S., where it appears to be native. Five populations collected on copper-enriched soils around shrines and temples in Tokyo are genetically monomorphic, but Asian populations from another Japanese site, India, and Nepal are exceptionally diverse in terms of numbers of alleles and multilocus haplotypes, total gene diversity (HT), and in the degree of differentiation among populations (measured as Nei's I and D). Long-distance dispersal has probably played an important role in the geographic history of S. cataractae, but the species appears to be native in both the New and Old Worlds. Gene flow between plants disjunct on different continents is insufficient to explain the lack of geographically correlated morphological and genetic differentiation in S. cataractae. © 1995 Springer-Verlag.
Bryophytes, including the mosses, liverworts, and hornworts, occur in a variety of habitats with high concentrations of metals and have other characteristics that are advantageous for studies of metal tolerance. Mosses may evolve genetically specialized, metal-tolerant races less frequently than flowering plants. Some species of mosses appear to have inherently high levels of metal tolerance even in individuals that have not been subjected to natural selection in contaminated environments. Scopelophila cataractae, one of the so-called copper mosses, not only tolerates extremely high concentrations of metals in its substrates, but requires these substrates for optimum growth. This species should be included in mechanistic studies of tolerance at the cellular and molecular levels.
Brachymenium deceptivum, known only from the type specimen, is described from Ethiopia. It is immediately distinguished from all other species of the genus by its complete lack of an exostome. © 1994 The New York Botanical Garden.
In Scopelophila cataractae (Pottiaceae) only the haploid gametophyte generation exists in the USA, although sporophytes occur in tropical America and in Asia. Over 50% of US plants in every population were devoid of gametangia, and no population contained plants with both male and female gametangia. Morphological differences between plants from putative male and female populations suggested gametophytic sexual dimorphism, but generalized sexual differences were not maintained under common garden conditions. Growth on soils with low, moderate, or high concentrations of metals demonstrated extensive morphological variability, and thus genetic polymorphism, among five asexual populations. Morphological traits were also significnatly plastic in response to differing soil types. All populations produced higher cover area and individual plants formed larger leaves on the most highly metal-contaminated soil. -from Author
A survey of 11 populations of Ceratodon purpureus showed that sex ratios are heterogeneous, but that female biases occur in more than half the populations: 160 single spore isolates representing 40 sporophytes from one population demonstrated that female gametophytes outnumbered males by a ratio of 3:2 at the time of germination. Female gametophytic clones formed significantly more biomass than male clones, and individudal female shoots were more robust. Male clones, however, produced more numerous stems. These sexually dimorphic traits may be related to life history differences between male and female gametophytes since females must provide nutritional support to the "parasitic' sporophyte generation, a burden that males do not share. -from Authors
Evolutionary capacity can be thought of as the capacity for speciation, or as the rate at which a population responds to natural selection. The genetic structures of lichen and bryophyte species are described in relation to such evolutionary capacity. A pressing problem with lichens is the question of what constitutes an individual, with a better understanding required of the genetic and evolutionary relationships between phycobiont and mycobiont. -P.J.Jarvis
Patterns of phenotypic and genotypic variability in two populations of Funaria hygrometrica were investigated using measurements of gametophytic and sporophytic morphology, sporophytic reproductive output, spore germination, gametophytic growth rates and tolerances of Cu, Cd, and low nutrient conditions, and electrophoretically detectable enzyme variation. Somatic mutation and/or nongenetic effects appear to contribute significantly to phenotypic variability in natural populations. -from Author
Gametophytic plants from six populations were grown on substrates with varied degrees of heavy-metal contamination in order to assess the effects of metal pollution on growth, leaf size, and formation of archegonia and antheridia. Plants from several populations that originated in uncontaminated habitats grew as well on mine soil as plants from a mine-site populations, suggesting an absence of ecotypic differentiation. -from Authors
Two populations of Funaria flavicans, were grown on nutrient media varying in Ni and Cr concentration and in the ratio of Mg and Ca. There was no evidence that serpentine plants were more tolerant of Ni, Cr, Mg/Ca, or high Ni combined with high Mg/Ca. Plants from the nonserpentine population produced more protonemal growth than the serpentine plants on every medium except the control, on which plants from the two populations were indistinguishable. Large differences in Ni tolerance among haploid sib families (families of meiotic progeny derived from the same sporophyte) from the nonserpentine site provided evidence of genetic polymorphism in that population. -from Author
Protonemal growth in populations collected from most Cu-contaminated soils was inhibited by only 10-30% on media with 10 μg g -1 Cu, whereas populations from other sites were inhibited by >80%. Population differences in tolerance of Zn, Cd and Ni were not clearly related to environmental contamination by these metals. Variation among populations in growth on the metal treatments (except Cu) was related to generalized differences in growth rates rather than to metal tolerance per se. Populations differed by up to 400% in the propensity to form stems on control nutrient medium, and stem formation was negatively correlated with protonemal growth, suggesting trade-offs between these 2 stages of gametophyte development. In comparison with flowering plants, generalized vigor and cross-tolerance between metals may play a more important part in the ability of F. hygrometrica to colonize contaminated oils, and metal-specific tolerant ecotypes may be less important. -from Author
Tolerances of 2 life history stages (protonemal growth and stem production) showed significant variation among populations, and among individuals within all populations. Heritabilities for tolerance were high within 3 populations, but were close to zero within a population that originated on a copper mine. -from Author
Scopelophila cataractae is known from several sites in S Arizona and occurs at 6 localities in the E USA. Chemical analyses of substrates from the E US localities showed that all but 1 population grew on Cu-enriched soil. The one substrate sample low in Cu was very high in Fe. Plants from 5 of the 6 localities were grown experimentally on 4 soil types ranging from highly to not contaminated, and all grew best on the soil contaminated with Cu, Pb and Zn. There was no significant variation in growth between populations on the four soil treatments. This lack of population differentiation may be related to the absence of sexual reproduction in S. cataractae in North America. from Author
The effect of pretreatment on zinc- and copper-enriched media on subsequent tolerance of F. hygrometrica to these metals was tested in three individuals each from a tolerant and a nontolerant population. Some individuals showed a significant response to pretreatment and some did not, and those that did varied in both intensity and direction. In general, pretreatment affected protonemal growth more than stem production. Although pretreatment effects were demonstrated, genetic differences between individuals and populations were more important determinants of the level of tolerance.
Tolerance of Funaria hygrometrica to Cu and Zn was greater in populations that originated on soil with high concentrations of these metals. Protonemal growth was more inhibited by the metals than was germination; Cu was more toxic than Zn. The pattern of population differentiation for heavy metal tolerance in this species is much like that of flowering plants. Five populations of Physcomitrium pyriforme, which does not occur on metal-contaminated soil, were all highly tolerant of Zn but extremely intolerant of Cu. Significant variation in tolerance to Cu and Zn occurred among populations, but tolerance did not correlate with metal contents in native substrates. This pattern differs from that of flowering plants. from Authors
Relationships between the ecological niche and species concepts are discussed by developing concepts of the niche and of character and species hypervolumes. Ecological data are best used to evaluate the biological/evolutionary significance of species defined by other criteria. Differences in patterns of ecological variation are as important for delineating species as are differences in the average or typical habitat. A classification of nine gemmiferous Pohlia species summarizes more ecological than morphological information, although the classification was based on morphology. Combining P. annotina and P. camptotrachela results in a loss of ecological information. -from Author
Forty-one Pohlia taxa coded for their expression of 36 qualitative morphological characters are analyzed using cladistic and phenetic methods. Four major lineages within the genus differ primarily in sporophyte characters, with specific differences based largely on gametophytic features. An infrageneric classification is proposed with diagnostic descriptions and nomenclature provided. -from Author