The Identification of Plants.

The major service that is provided by a herbarium is the provision of the correct scientific name for any piece of plant material that is brought in for naming.

In order to do this all the specimens in the herbarium must be previously identified, and classified into species (plural species), genus (plural genera) and family (plural families), so that the unknown specimens can be compared with the sheets in the collection.

This is not always an easy matter, especially as the names of plants do not necessarily remain constant with time!

Because of the changes in the names of plants it is also necessary periodically to re-arrange the herbarium sheets, and even relabel them. It is also necessary to update the check-lists from time to time to reflect the new names.

The classification and naming of the plant specimens is the job of taxonomists. A taxon (plural taxa) is a taxonomic group of plants of any rank, although it is more often applied to a species, such as Lycopersicon esculentum (Tomato), rather than to a genus (e.g. Lycopersicon) or to a family (e.g. Solanaceae).

Taxonomists are constantly trying to improve our knowledge of the relationships between plant species. In doing this they may rename individual specimens, move species into different genera, and even change their relationships at family level.

If they were allowed to do this by individual whim there would be chaos, but in fact there are very strict rules that must be applied to the naming of plants. It must be done according to the International Code of Botanical Nomenclature. This involves describing each species in Latin or Latinized form, and validating the names they suggest by a set of very precise rules. This work must then be published so that other taxonomists can agree or disagree, and the new names become known on a world basis.

Structure of Plant Names

The full name of each species of plant is binomial, that is, it consists of two words. the generic and the specific names. Species are grouped into genera. The genera are also grouped, this time into families.

The first name of a species is its generic name, the name of the genus to which it belongs (e.g. Lycopersicon). It always starts with a capital letter. The names of genera are Latin or Latinized nouns.

The second, the specific epithet, always starts with a common letter (e.g. esculentum - meaning 'edible'), and usually acts as an adjective.

After the generic and specific names is a personal name or its standard abbreviation. Thus Lycopersicon esculentum Mill. where Mill. is the abbreviaton for Miller.

Types

The proper name for a taxon is linked to a type. The type for a species, for example, is the actual specimen (sometimes a drawing) upon which the original description was based.

Type specimens are specially marked so that they can easily be found, and receive extra care in the herbarium.

The type specimen referred to above is called a holotype. If there are duplicates, part of the same collection, these are known as isotypes.

If the original material has got lost a subsequent author may designate a neotype to act as the type.

The Correct Name

The correct name for a species is normally the earliest name that is 'validly' and 'effectively' published according to the latest version of the Botanical Code.

All other names given to the species are known as synonyms, and in a check-list or taxonomic monograph it it important to list them, in descending order of time of publication - latest first, so that readers will be sure which plant is being discussed.