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.
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.
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.
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.
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.