Genus

"Genera" redirects here. For the operating system, see Genera (operating system). For other uses, see Genus (disambiguation).
Template:Biological classification
A **genus** (/ˈdʒiːnəs/, pl. **genera**) is a taxonomic rank used in the biological classification of living and fossil organisms in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

E.G., *Felis catus* and *F. silvestris* are two species within the genus *Felis*. *Felis* is a genus within the family Felidae.
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:

1. monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage ).
2. reasonable compactness – a genus should not be expanded needlessly; and
3. distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; note that DNA sequences are a *consequence* rather than a *condition* of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).

Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.

## Name

The term comes from the Latin *Template:Linktext* ("origin; type; group; race"), a noun form cognate with *gignere* ("to bear; to give birth to"). It probably came to Latin from the Arabic: *Gins* جنس‎ meaning type. **Script error: No such module "Unsubst".** 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".

## Use

The scientific name of a genus may be called the **generic name** or **generic epithet**: it is always capitalized. It plays a pivotal role in binomial nomenclature, the system of naming organisms.

### Binomial nomenclature

*Main articles: Binomial nomenclature, Trinomen, and Infraspecific names*
The rules for the scientific names of organisms are laid down in the Nomenclature Codes, which are employed by the speakers of all languages, giving each species a single unique Latinate name. The standard way of scientifically describing species and other lower-ranked taxa is by binomial nomenclature. The generic name forms its first half. 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. 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. Especially with these longer names, when the generic name is known from context, it is typically shortened to its initial letter.

Because animals are typically only grouped within subspecies, it is simply written as a trinomen with a third name. For example, because dogs are still so similar to wolves as to form part of their species but so distinct as to require separate treatment, they are described as *C. lupus familiaris* (Lat. "domestic"), while the "wolves" form many distinct subspecies, including the common wolf (*C. lupus lupus*) and the dingo (*C. lupus dingo*). Dog breeds, meanwhile, are not scientifically distinguished.

There are several divisions of plant species and therefore their infraspecific names generally include contractions explaining the relation. For example, the genus *Hibiscus* (Lat. "marshmallow") includes hundreds of other species apart from the Rose of Sharon or common garden hibiscus (*H. syriacus*, from Lat. "Syrian"). Rose of Sharon doesn't have subspecies but has cultivars that carry desired traits, such as the bright white *H. syriaca* 'Diana'. "Hawaiian hibiscus", meanwhile, includes several separate species. Since not all botanists agree on the divisions or names between species, it is common to specify the source of the name using author abbreviations. For example, *H. arnottianus* A.Gray was first specified in a work by Asa Gray. Sister Roe identified an immaculate white hibiscus on Molokai as a separate species, but D.M. Bates later reclassified it as a subspecies of *H. arnottianus*. It thus now appears as *H. arnottianus* ssp. *immaculatus* or as *H. arnottianus* A.Gray subsp. *immaculatus* (M.J.Roe) D.M.Bates. When it is considered a mere variety of *H. arnottianus*, it is written *H. arnottianus* var. *immaculatus*.

### Type

See also: type genus, type species and type specimen
Each genus should have a designated type, although in practice there is a backlog of older names without one. In zoology, this is the type species and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed.

### Identical names

Within the same kingdom one generic name can apply to only one genus. This is why the platypus belongs to the genus *Ornithorhynchus*: although George Shaw named it *Platypus* in 1799, that name had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. Since beetles and platypuses are both members of the kingdom Animalia, the name could not be used for both. Johann Friedrich Blumenbach published the replacement name *Ornithorhynchus* in 1800.

However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for Algae, Fungi, and Plants, there are some five thousand such names in use in more than one kingdom. For instance, *Anura* is the name of the order of frogs but also is the name of a non-current genus of plants; *Aotus* is the generic name of both golden peas and night monkeys; *Oenanthe* is the generic name of both wheatears and water dropworts; *Prunella* is the generic name of both accentors and self-heal; and *Proboscidea* is the order of elephants and the genus of devil's claws.

### Higher classifications

The type genus forms the base for higher taxonomic ranks, such as the family name *Canidae* ("Canids") based on *Canis*. However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is *Carnivora* ("Carnivores").

## Size

 File:Number of reptile genera with a given number of species.png
The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles, which have about 1180 genera, most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5-10 species, ~200 have 11-50 species, and only 27 genera have more than 50 species (see figure). However, some insect genera such as the bee genera *Lasioglossum* and *Andrena* have over 1000 species each.

Which species are assigned to a genus is somewhat arbitrary. Although all species within a genus are supposed to be "similar" there are no objective criteria for grouping species into genera. There is much debate among zoologists whether large, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance, the lizard genus *Anolis* has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets.

## See also

* List of the largest genera of flowering plants
* Genus–differentia definition

## References

1. ↑ Gill, F. B.; Slikas, B.; Sheldon, F. H. (2005). "Phylogeny of titmice (Paridae): II. Species relationships based on sequences of the mitochondrial cytochrome-b gene". *Auk* **122** (1): 121–143. doi:10.1642/0004-8038(2005)122[0121:POTPIS]2.0.CO;2.
2. ↑ De la Maza-Benignos, M. , Lozano-Vilano, M.L., & García-Ramírez, M. E. (2015). Response paper: Morphometric article by Mejía et al. 2015 alluding genera Herichthys and Nosferatu displays serious inconsistencies. Neotropical Ichthyology, 13(4), 673-676.http://www.scielo.br/scielo.php?pid=S1679-62252015000400673&script=sci\_arttext
3. ↑ De la Maza-Benignos, M., Lozano-Vilano, M. L., & García-Ramírez, M. E. (2015). Response paper: Morphometric article by Mejía et al. 2015 alluding genera Herichthys and Nosferatu displays serious inconsistencies. Neotropical Ichthyology, 13(4), 673-676.http://www.scielo.br/scielo.php?pid=S1679-62252015000400673&script=sci\_arttext
4. ↑ Merriam Webster Dictionary
5. ↑ Stuessy, T. F. (2009). *Plant Taxonomy: The Systematic Evaluation of Comparative Data* (2nd ed.). New York: Columbia University Press. p. 42. ISBN 9780231147125.
6. ↑ "*Hibiscus syriacus* 'Diana'", *Plants*, Royal Horticultural Society, 2015, retrieved 7 October 2015 .
7. ↑ *United States Exploring Expedition during the years 1838, 1839, 1840, 1841, 1842 under the Command of Charles Wilkes, U.S.N.*, Vol. XV: *Botany*, Pt. I*, Philadelphia, 1854**.*
8. ↑ Roe, Margaret James (1961), "A Taxonomic Study of the Indigenous Hawaiian Species of the Genus *Hibiscus* (Malvaceae)" (PDF), *Pacific Science*, Vol. 15, No. 1 .
9. ↑ Bates, David Martin (1989), *Occasional Papers of the Bernice Pauahi Bishop Museum of Polynesian Ethology and Natural History*, Vol. 29, No. 104 .
10. ↑ The Reptile Database
11. ↑ Nicholson, K. E.; B. I. Crother, C. Guyer & J.M. Savage (2012) It is time for a new classification of anoles (Squamata: Dactyloidae). Zootaxa 3477: 1–108

## External links

* Nomenclator Zoologicus: Index of all genus and subgenus names in zoological nomenclature from 1758 to 2004.
* Fauna Europaea Database for Taxonomy

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