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A genus (,   genera ) is a taxonomic rank used in the biological classification of and in . In the hierarchy of biological classification, genus comes above 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. and are two species within the genus . Felis is a genus within the family .

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

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


Name
The term comes from the ("origin; type; group; race"), Merriam Webster Dictionary a noun form cognate with gignere]] ("to bear; to give birth to"). 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".
(2018). 9780231147125, Columbia University Press.


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 .


Binomial nomenclature
The rules for the names of are laid down in the Nomenclature Codes, which are employed by the speakers of all languages, giving each species a single unique name. The standard way of scientifically describing and other lower-ranked is by binomial nomenclature. The generic name forms its first half. For example, the 's binomial name is with (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 names in or a variety of infraspecific names in . 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 with a third name. For example, because 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 (Lat. "domestic"), while the "wolves" form many distinct subspecies, including the and the . , 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 (Lat. "marshmallow") includes hundreds of other species apart from the Rose of Sharon or common garden hibiscus from Lat. ""). Rose of Sharon doesn't have subspecies but has that carry desired traits, such as the bright red . "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, was first specified in a work by .. Sister Roe identified an immaculate white hibiscus on as a separate species,. but D.M. Bates later reclassified it as a subspecies of H. arnottianus.. It thus now appears as or as subsp. When it is considered a mere variety of it is written


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


Identical names (synonyms and homonyms)
Within the same kingdom one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example, the belongs to the genus Ornithorhynchus although named it Platypus in 1799 (these two names are thus synonyms ) . However, the name Platypus had already been given to a group of by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym. 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 but also is the name of a non-current genus of plants;
  • Aotus is the generic name of both golden peas and ;
  • Oenanthe is the generic name of both and ;
  • Prunella is the generic name of both and ; and
  • Proboscidea is the order of and the genus of devil's claws.
  • The name of the genus Paramecia (an extinct red algae) is also the plural of the name of the genus (which is in the SAR supergroup), which can also lead to confusion.
A list of generic homonyms has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG)


Higher classifications
The forms the base for higher ranks, such as the family name ("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 ("Carnivores").


Size

The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) , which have about 1180 genera, the 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).The Reptile Database However, some insect genera such as the bee genera and 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 has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets.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


See also
  • List of the largest genera of flowering plants
  • Genus–differentia definition


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