A genus (, genera ) is a taxonomic rank used in the biological classification of extant taxon and fossil 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 Felis 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:
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
[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]).
reasonable compactness – a genus should not be expanded needlessly; and
distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly gene flow (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]
The term comes from the Latin
("origin; type; group; race"),
[ Merriam Webster Dictionary]
a noun form cognate with gignere]]
("to bear; to give birth to"). 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".
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
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
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 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 domestic dog 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 Eurasian wolf and the dingo . , 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 from Lat. ""). Rose of Sharon doesn't have subspecies but has cultivars 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 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 or as subsp. When it is considered a mere variety of it is written
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 taxon
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 platypus
belongs to the genus Ornithorhynchus
although George Shaw
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
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 self-heal; 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 Paramecium (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
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
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 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.
[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]
List of the largest genera of flowering plants