See genus (mathematics) for the use of the term in mathematics.

In biology, a genus (plural genera) is a grouping in the classification of living organisms having one or more related or morphologically similar species. In the common binomial nomenclature, the name of an organism is composed of its genus (capitalized) and a species identifier. An example is Homo sapiens, the name for the human species which belongs to the genus Homo.

See scientific classification for more details of this system.

The Type Genus of a taxon is the first genus to be named and described. Families and, in plants, all taxa up to division are named after the type genus. The genus and these taxa are typified by a specimen that shows the characteristics of the genus best. The specimen used to describe this species is kept as the holotype in a zoological museum or a herbarium to be available for further study.

A genus name in one kingdom is allowed to be the same as a genus or other taxon name in another kingdom. For instance, Anura is a genus of plants as well as the order of frogs; Aotus is both a pea and a monkey. It is, however, not allowed for two genera in the same kingdom to have the same name; this explains why the platypus is called Ornithorhynchus--"platypus" was originally chosen, but the name had already been given to an obscure invertebrate (invertebrates are in the same kingdom, Animalia, as the platypus).

See also: Linnaean taxonomy, cladistics