What is a Herbarium?

What is an Herbarium?

An herbarium (plural: herbaria) is a collection of preserved plant specimens maintained for scientific purposes. Specimen are curated (pressed and dried), mounted on rigid paper (100% rag content), and filed in cabinets (metal or wood), using techniques perfected over several centuries. Other specimens are preserved in liquid (alcohol or formalin) or dried three-dimensionally. Properly curated and protected plant specimens will last indefinitely. All specimens are accompanied by data indicating where they were collected, when, and by whom.

How are Specimens Obtained? Specimens accessioned into the herbarium are collected by faculty, students, amateur botanists, non-academic professionals, including agency biologists, and environmental consultants. Amateur botanists collected many of our noteworthy specimens. Other specimens were received as gifts sent for identification and university affiliated expeditions.

As a common practice, collectors generally prepare several duplicates of each voucher specimen, depending on how common the plants are. The best specimen is kept at the home institution, while the duplicates are exchanged for other duplicates collected at other institutions from around the world. The exchange of specimens between herbaria is an effective means for participating institutions to amass much more diverse collections. It also provides a degree of "insurance," diminishing the scientific impact if a catastrophe destroys any one institution.

Who Uses Herbarium Specimens? At TTU, herbarium specimens are used in botany classes to provide students with examples of the botanical diversity. The collections are also used as an outreach to the general public and the private sectors, which need comparative material in conjunction with plant identification. However, the most significant use is by the scientific community, particularly plant systematists, in the preparation of monographs or floras.

What Do Herbarium Specimens Represent? A herbarium specimen is a voucher documenting a species growing at a given site at certain time. As such, herbarium holdings worldwide collectively provide the raw data underpinning our scientific knowledge of what species exists, what their diagnostic features are, what range of variation exists within each species, and where each species occurs. If the herbaria of the world were to cease to exist, the preparation of monographs and floras would be very incomplete and/or inaccurate. In this regard the herbaria of the world play an important role in the scientific heritage of humans.

Why Keep More than One Voucher Specimen? Multiple specimens are needed to document the variability (phenotypic plasticity) that exists within a species. The variation of a species is driven by many factors such as growing conditions, time of year, and age. For example, multiple size and shapes of leaves of the same species (heterophylly). Among terrestrial plants shade leaves are larger than sun leaves and in aquatic plants aerial leaves are larger that submerged leaves.

What is a Type Specimen? By accepted convention, a single specimen of each species is designated as the "type specimen." The type specimen gains its importance in its role of anchoring nomenclature. It is the name-bearer, providing an unequivocal way of linking a name with a single representative of the species. All other specimens are linked to the name secondarily, by virtue of their acceptance as members of the same species. If, for example, what was considered to be one species is determined to be two, then the given name goes to the subunit that includes the type specimen. It is important to realize that the type specimen is not necessarily more "typical" than any other specimen, due to the variability that exist among species. In fact, there are numerous examples of "atypical" type specimens, collected at the margin of the species range.

Why Do Scientific Names Keep Changing? Names of plants are changed for one of three reasons. First, there are legal reasons involving the accepted rules of botanical nomenclature; e.g., an earlier validly published name comes to light. Second, there are changes resulting from shifts in taxonomic philosophies, such as those exemplified by "splitters" and "lumpers," or a rejection of paraphyly. Most important, however, are those changes resulting from an increased understanding of the species themselves, which can be perceived as hypothesis. Initial hypotheses on what the species exist, and what their diagnostic characteristics are, are often based on only a handful of specimens. The hypotheses are tested whenever more specimens become available for examination, or when novel characters are examined (including molecular evidence). Sometimes the initial hypotheses are supported; other times they are refuted or modified to reflect new evidence. This in turn can affect the appropriate nomenclature. The on-going name changes accordingly do not indicate simple equivocation on the part of taxonomists, but rather are accurate reflection of the dynamic nature of our scientific understanding of the plant kingdom.

Text written Dr. Felix Coe, copyright 2005.