The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.
The term comes from the Latin genus ("origin; type; group; race"), a noun form cognate with gignere ("to bear; to give birth to"). Linnaeus popularized its use in his 1753 Species Plantarum, but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera".
The rules for the scientific names of organisms are laid down in the Nomenclature Codes, giving each species a single unique name which is Latin in form and, by contrast with a common name, is language-independent. Except for viruses, the standard format for a species name comprises a generic name (which indicates the genus to which the species belongs) followed by a specific epithet. For example, the gray wolf's binomial name is Canis lupus, with Canis (Lat. "dog") being the generic name shared by the wolf's close relatives and lupus (Lat. "wolf") being the specific name particular to the wolf; a botanical example would be Hibiscus arnottianus, a species of hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany. When the generic name is already known from context, it may be shortened to its initial letter, for example C. lupus in place of Canis lupus. Where species are further subdivided, the generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example Canis lupus familiaris for the domestic dog (when considered a subspecies of the gray wolf) in zoology, or as a botanical example, Hibiscus arnottianus ssp. immaculatus. Also, as visible in the above examples, the latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics.