Genus
Genus (/ˈdʒiːnəs/ pl.: genera /ˈdʒɛnərə/) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses.[1] In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
For other uses, see Genus (disambiguation).
The composition of a genus is determined by taxonomists. 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,[2][3] 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.[4]
Etymology[edit]
The term "genus" comes from Latin genus, a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl 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".[5]
The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of a total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year.[12] "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses[1] and prokaryotes,[13] while for others there are compendia with no "official" standing such as Index Fungorum for fungi,[14] Index Nominum Algarum[15] and AlgaeBase[16] for algae, Index Nominum Genericorum[17] and the International Plant Names Index[18] for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus[19] and the Index to Organism Names for zoological names.
Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom:
The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names; the values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes.
Within Animalia, the largest phylum is Arthropoda, with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up the largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae).
By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species,[20] also including genus names only (no species) for some groups.