A genus (/ˈdʒiːnəs/, pl. genera /ˈdʒɛnərə/) 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.
Felis catus and
Felis silvestris are two species within the genus
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).
reasonable compactness – a genus should not be expanded needlessly;
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 inhibit gene flow (e.g.
Moreover, genera should be composed of phylogenetic units of the same
kind as other (analogous) genera.
2.1 Binomial nomenclature
2.3 Identical names (synonyms and homonyms)
2.4 Higher classifications
4 See also
6 External links
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
Joseph Pitton de Tournefort
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.
Main articles: Binomial nomenclature, Trinomen, and Infraspecific
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
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
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
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 red 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.
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
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
already been given to a group of ambrosia beetles 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 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.
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 (IRMNG)
The type genus forms the base for higher taxonomic ranks, such as the
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
Number of reptile genera with a given number of species. Most genera
have only one or a few species but a few may have hundreds. Based on
data from the
Reptile Database (as of May 2015).
The number of species in genera varies considerably among taxonomic
groups. For instance, among (non-avian) reptiles, 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). However,
some insect genera such as the bee genera
Lasioglossum and Andrena
have over 1000 species each. The largest flowering plant genera,
Astragalus, contains over 3,000 species.
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.
List of the largest genera of flowering plants
^ Gill, F. B.; Slikas, B.; Sheldon, F. H. (2005). "Phylogeny of
titmice (Paridae): II.
Species relationships based on sequences of the
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^ a b de la Maza-Benignos, Mauricio; Lozano-Vilano, Ma. de Lourdes;
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^ Merriam Webster Dictionary
^ Stuessy, T. F. (2009). Plant Taxonomy: The Systematic Evaluation of
Comparative Data (2nd ed.). New York: Columbia University Press.
p. 42. ISBN 9780231147125.
Hibiscus syriacus 'Diana'", Plants, Royal Horticultural Society,
2015, retrieved 7 October 2015 .
^ 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 .
^ Roe, Margaret James (1961), "A
Taxonomic Study of the Indigenous
Species of the
Hibiscus (Malvaceae)" (PDF), Pacific
Science, Vol. 15, No. 1 .
^ Bates, David Martin (1989), Occasional Papers of the Bernice Pauahi
Bishop Museum of Polynesian Ethology and Natural History,
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^ "IRMNG - Homonyms". www.irmng.org. Retrieved 2016-11-17.
^ Frodin, David G. (2004). "History and concepts of big plant genera".
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^ Nicholson, K. E.; Crother, B. I.; Guyer, C.; Savage, J.M. (2012).
"It is time for a new classification of anoles (Squamata:
Dactyloidae)" (PDF). Zootaxa. 3477: 1–108.
Interim Register of Marine and Nonmarine Genera (IRMNG)
Nomenclator Zoologicus: Index of all genus and subgenus names in
zoological nomenclature from 1758 to 2004.
Fauna Europaea Database for Taxonomy