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Nomenclature

By Alexander Krings, Curator (N. C. State University Department of Plant Biology Herbarium)

The Oxford English Dictionary defines nomenclature as "the allocation of Latin names to species and other taxa." To facilitate unambiguous communication about organisms, every taxon must bear a unique scientific name. International rules have been established that govern the application of such names. For plants, the governing rules are laid out in the International Code of Botanical Nomenclature or ICBN.

Among the central tenets of the ICBN is that each name must be validly and effectively published, adhere to the required format of a binomial, include a description or diagnosis in Latin, and be typified by a voucher specimen. The voucher specimen designated by the scientist naming a new species is called a "type." Types serve as standards for the application of a name. The scientific name itself must be a binomial-that is, it must consist of a genus name and a specific epithet.

For example, the binomial scientific name for white oak, a common tree in North Carolina, is Quercus alba L. "Quercus" is the genus, "alba" the specific epithet, and "L." the standardized abbreviation for Carl Linnaeus, the scientist first describing the species. You may sometimes read that "alba" represents the species name, but this is incorrect. The species name is the combined genus name and the specific epithet, or "Quercus alba" in our example.

flowerScientific names are more than unique identifiers however, they are also designed to reflect evolutionary relationships and are applied by taxonomists only after careful study. Scientific names reflect one of the central aims of taxonomy: to provide a predictive organismal classification. The classification is derived from synthesis of available morphological, cytological, ecological, and molecular data through phylogenetic analysis. Ranks-such as family, genus, and species-are used to indicate successive hierarchy in relationship. Thus, for example, all species referred to the genus Quercus L. are more closely related to one another than they are to species in the genus Fagus L. Both Quercus and Fagus are however assigned to the family Fagaceae, indicating that the two genera are more closely related to one another than either is to another family.

The development of a predictive organismal classification is useful as it allows inference of properties. So, for example, if a chemical with anti-cancer activity is isolated in one species, a frequently successful search strategy to find other sources of the chemical or variations thereof that might be even more useful is to concentrate first on related species. It is particularly useful to know where on the tree of life to search when important chemicals that cannot be synthesized in the lab have been isolated from rare species. Finding more common species exhibiting a similar chemical then becomes of utmost importance. Without a classification built on understanding of evolutionary relationships, such searches essentially would be akin to finding a needle in a haystack and a waste of time and resources.

The pursuit of a predictive classification based on evolutionary relationships is an on-going effort and far from complete. Estimates of the total number of plant species range from 250,000 to 500,000, and our knowledge of plants particularly in the tropics and hotspots of diversity is very incomplete. Also, with the advent of approaches utilizing molecular data, vast new amounts of data are now available to be analyzed and used in the estimation of phylogenies. In many cases, molecules have supported prior classifications, but in some spectacular cases relationships have become evident that were previously obscured.

To be useful, scientific names must reflect our most recent understanding of evolutionary relationships and must therefore be changed when they do not. Accordingly, in an extreme case, you might find a different scientific name for the same species in a taxonomic manual published in 1933, 1968, and 2006. However, rather than bemoaned, this should be celebrated and appreciated for the progress it represents. How can one expect taxonomists in the 1930s, without access to modern molecular laboratories, much less to the knowledge base generated in the intervening period, to have been able to produce a 100% accurate and unassailable classification? Name changes are the inevitable outcome of progress in taxonomy.

plantFor the purposes of the Wells project, two scientific names are shown-the name used by B.W. Wells in his publications and a "modern" name. Dr. Alan Weakley's draft Flora of the Carolinas, Virginia, and Georgia, and Surrounding Areas was chosen as the basis for the modern names. The nomenclature followed by Dr. Weakley is a synthesis of hundreds of recent studies and thus can be considered an appropriate representation of our best classification at this point in time for species occurring in the area of coverage.





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