In botany, an infraspecific name is the scientific name for any taxon below the rank of species, i.e. an infraspecific taxon. The scientific names of botanical taxa are regulated by the International Code of Nomenclature for algae, fungi, and plants. 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. 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.
Construction of infraspecific names
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:
Although the "connecting terms" mentioned above to indicate rank, such as "var.", are the recommended ones, the ICN allows for other connecting terms in validly published infraspecific taxa. It specifically mentions that Greek letters α, β, γ, etc. can be used in this way in the original document and further ranks may be added without limit. Names which use these connecting terms are now deprecated, but they have an importance because they can be basionyms of current species. The commonest cases use "β" and "b"; examples mentioned in the ICN are Cynoglossum cheirifolium β. Anchusa and Polyporus fomentarius β. applanatus whilst other examples are Agaricus plexipes b fuliginaria and Peziza capula ß cernua. The ICN allows the possibility that a validly published name could have no defined rank and uses "" as the connecting term in such cases.
Abbreviation of infraspecific names
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.
Legitimate infraspecific names
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.
As soon as a subspecies of Poa secunda was created, then the type specimen of P. secunda immediately became the type specimen of Poa secunda subsp. secunda. The name "Poa secunda subsp. secunda" was automatically created. Soreng created the subspecies Poa secunda subsp. juncifolia, thereby making the type specimen of P. secunda also the type specimen of Poa secunda subsp. secunda.
If in addition to the subspecies any variety of Poa secunda were to be created, then the type specimen of P. secunda would automatically become the type specimen of Poa secunda var. secunda. The type specimen would then have the classification Poa secunda subsp. secunda var. secunda.
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. juncifoliaif, and only if, the type specimen of Poa secunda f. juncifolia is the same as the type specimen of Poa secunda subsp. 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.
Specifying authors
When indicating authors for infraspecific names, it is possible to show either just the author 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.
Cultivated plants
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. Although logically below the rank of species, 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.
