Nomenclature
In zoology, the International Code of Zoological Nomenclature (4th edition, 1999) accepts only one rank below that of species, namely the rank of subspecies . Other groupings, "infrasubspecific entities" do not have names regulated by the ICZN. Such forms have no official ICZN status, though they may be useful in describing altitudinal or geographical clines, pet breeds, Transgenic Animals, etc. The scientific name of a subspecies is a binomen followed by a subspecific name, as Panthera tigris sumatrae (Sumatran Tiger). A name of this kind is called a trinomen.
In bacteriology, the only rank below species that is regulated explicitly by the code of nomenclature is subspecies, but infrasubspecific taxa are extremely important in bacteriology; Appendix 10 of the code lays out some recommendations that are intended to encourage uniformity in describing such taxa. Names published before 1992 in the rank of variety are taken to be names of subspecies (see International Code of Nomenclature of Bacteria).
In botany, subspecies is one of many ranks below that of species, such as variety, subvariety, form, and subform. The subspecific name is preceded by "subsp." or "ssp.", as Schoenoplectus californicus ssp. tatora (Totora). Note that all parts of the binomial are italicised except the actual word "subsp." or "ssp." Any botanical name including a subspecies, variety, etc., is called an infraspecific name.
Read more about this topic: Subspecies