In botany, an infraspecific name is the scientific name for any taxon below the rank of species, i.e. an infraspecific taxon. (A "taxon", plural "taxa", is a group of organisms to be given a particular name.) The scientific names of botanical taxa are regulated by the International Code of Nomenclature for algae, fungi, and plants (ICN). This specifies a 'three part name' for infraspecific taxa, plus a 'connecting term' to indicate the rank of the name. An example of such a name is Astrophytum myriostigma subvar. glabrum, the name of a subvariety of the species Astrophytum myriostigma (bishop's hat cactus).
Names below the rank of species of cultivated kinds of plants and of animals are regulated by different codes of nomenclature and are formed somewhat differently.
Article 24 of the ICN describes how infraspecific names are constructed. The order of the three parts of an infraspecific name is:
It is customary to italicize all three parts of such a name, but not the connecting term. For example:
The recommended abbreviations for ranks below species are, for example:
Like specific epithets, infraspecific epithets cannot be used in isolation as names. Thus the name of a particular species of Acanthocalycium is Acanthocalycium klimpelianum, which can be abbreviated to A. klimpelianum where the context makes the genus clear. The species cannot be referred to as just klimpelianum. In the same way, the name of a particular variety of Acanthocalycium klimpelianum is Acanthocalycium klimpelianum var. macranthum, which can be abbreviated to A. k. var. macranthum where the context makes the species clear. The variety cannot be referred to as just macranthum.
Sometimes more than three parts will be given; strictly speaking, this is not a name, but a classification. The ICN gives the example of Saxifraga aizoon var. aizoon subvar. brevifolia f. multicaulis subf. surculosa; the name of the subform would be Saxifraga aizoon subf. surculosa.
For a proposed infraspecific name to be legitimate it must be in accordance with all the rules of the ICN. Only some of the main points are described here.
A key concept in botanical names is that of a type. In many cases the type will be a particular preserved specimen stored in a herbarium, although there are other kinds of type. Like other names, an infraspecific name is attached to a type. Whether a plant should be given a particular infraspecific name can then be decided by comparing it to the type.
There is no requirement for a species to be divided into infraspecific taxa, of whatever rank; in other words, a species does not have to have subspecies, varieties, forms, etc. However, if infraspecific ranks are created, then the name of the type of the species must repeat the specific epithet as its infraspecific epithet. The type acquires this name automatically as soon as any infraspecific rank is created. As an example, consider Poa secunda J.Presl, whose type specimen is in the Wisconsin State Herbarium.
The same epithet can be used again within a species, at whatever level, only if the names with the re-used epithet are attached to the same type. Thus there can be a form called Poa secunda f. juncifolia as well as the subspecies Poa secunda subsp. juncifolia if, and only if, the type specimen of Poa secunda f. juncifolia is the same as the type specimen of Poa secunda subsp. juncifolia (in other words, if there is a single type specimen whose classification is Poa secunda subsp. juncifolia f. juncifolia).
If two infraspecific taxa which have different types are accidentally given the same epithet, then a homonym has been created. The earliest published name is the legitimate one and the other must be changed.
When indicating authors for infraspecific names, it is possible to show either just the author(s) of the final, infraspecific epithet, or the authors of both the specific and the infraspecific epithets. Examples:
In zoological nomenclature, names of taxa below species rank are formed somewhat differently, using a trinomen or 'trinomial name'. No connecting term is required as there is only one rank below species, the subspecies.
The ICN does not regulate the names of cultivated plants, of cultivars, i.e. plants specifically created for use in agriculture or horticulture. Such names are regulated by the International Code of Nomenclature for Cultivated Plants (ICNCP).
Although logically below the rank of species (and hence "infraspecific"), a cultivar name may be attached to any scientific name at the genus level or below. The minimum requirement is to specify a genus name. For example, Achillea 'Cerise Queen' is a cultivar; Pinus nigra 'Arnold Sentinel' is a cultivar of the species P. nigra (which is propagated vegetatively, by cloning).