A herbarium is a critical resource for biodiversity, ecological, and evolutionary research studies. It is a primary data source of dried and labeled plant specimens that is arranged to allow for easy retrieval access and archival storage. A herbarium is like a library, but differs in that the information is stored in a biological form––as pressed, dried, and annotated plant specimens (in the case of most vascular plants; lichens, fungi, bryophytes and some vascular plants are preserved slightly differently, although the main points are the same). The Duke Herbarium (DUKE) has acquired its specimens over time primarily through research-directed field collections by Duke faculty, staff, and students, but also by gift and exchange with other herbaria worldwide.
Herbaria consist of specimens that have been collected over broad geographic ranges and over many years. Multiple samples of individual species collected from different habitats are typically preserved so that variation among individuals can be documented, and related to ecological factors or evolutionary factors. Herbarium and museum collections comprise the basic materials for obtaining information about the world's biodiversity. Herbarium specimens also provide materials for research on variation at the DNA level, genome structure, and gene expression.
How did herbaria come to be?
Luca Ghini, professor of medicine and botany at the University of Pisa during the 16th century, is credited with the invention of the herbarium. Traditionally, several plant specimens were glued in a decorative arrangement on a single sheet of paper. These sheets were then bound into volumes, stored in a library, and cited like books. Specimens were thus placed into a fixed order from which they could not be removed without destroying the specimens. It was the famous Swedish naturalist Carolus Linnaeus who advised readers of his Philosophia Botanica in 1751 to mount just one specimen per sheet and refrain from binding the sheets together. For storage of the mounted specimens, Linnaeus suggested a specially-built cabinet where individual sheets could easily be inserted at any place, removed at any time, and reinserted again anywhere in the collection. In contrast to the bound volumes of older herbaria, the order that Linnaeus’ herbarium cabinet brought to his collection was not fixed into perpetuity. This “internal mobility” of the herbarium could accommodate the arrival of new material and enabled the user to repeatedly rearrange that material to reflect new knowledge.
For more information on LInnaeus' role in the devolopment of the modern herbarium, see this short article (featuring photos of Linnaeus' original cabinets and specimens!).
Creating herbarium specimens
See this video for a demonstration of the collection, pressing, and mounting of plant specimens.