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.