Genus ( plural genera ) is a
taxonomic rank used in the
biological classification of
living and
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s as well as
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es.
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. ''
Panthera leo'' (lion) and ''
Panthera onca'' (jaguar) are two species within the genus ''
Panthera''. ''Panthera'' is a genus within the family
Felidae.
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, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
#
monophyly – all descendants of an
ancestral
An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or ( recursively) the parent of an antecedent (i.e., a grandparent, great-grandparent, great-great-grandparent and so forth). ''Ancestor'' is "any person from wh ...
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
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
, or
biogeography;
DNA sequences
A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are us ...
are a ''consequence'' rather than a ''condition'' of diverging evolutionary lineages except in cases where they directly
inhibit
Inhibitor or inhibition may refer to:
In biology
* Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity
* Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotr ...
gene flow (e.g.
postzygotic barrier
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offsprin ...
s).
Moreover, genera should be composed of
phylogenetic units of the same kind as other (analogous) genera.
Etymology
The term "genus" comes from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
γένος, a noun form
cognate with ' ('to bear; to give birth to'). The Swedish taxonomist
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
popularized its use in his 1753 ''
Species Plantarum'', but the French botanist
Joseph Pitton de Tournefort
Joseph Pitton de Tournefort (5 June 165628 December 1708) was a French botanist, notable as the first to make a clear definition of the concept of genus for plants. Botanist Charles Plumier was his pupil and accompanied him on his voyages.
Lif ...
(1656–1708) is considered "the founder of the modern concept of genera".
Use
The scientific name (or the scientific epithet) of a genus is also called the generic name; in modern style guides and science it is always capitalised. It plays a fundamental role in
binomial nomenclature, the system of naming
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s, where it is combined with the scientific name of a
species: see
Botanical name and
Specific name (zoology).
Use in nomenclature
The rules for the
scientific names of
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s are laid down in the
nomenclature codes, which allow each species a single unique name that, for
animals (including
protists),
plants (also including
algae and
fungi) and
prokaryotes (
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
and
archaea), is
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
and binomial in form; this contrasts with
common or vernacular names, which are non-standardized, can be non-unique, and typically also vary by country and language of usage.
Except for
viruses, the standard format for a
species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the
gray wolf's scientific name is with ''
Canis
''Canis'' is a genus of the Caninae which includes multiple extant species, such as wolves, dogs, coyotes, and golden jackals. Species of this genus are distinguished by their moderate to large size, their massive, well-developed skulls and de ...
'' (
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
for 'dog') being the generic name shared by the wolf's close relatives and (Latin for 'wolf') being the specific name particular to the wolf. A botanical example would be ''
Hibiscus arnottianus'', a particular species of the genus ''
Hibiscus
''Hibiscus'' is a genus of flowering plants in the mallow family, Malvaceae. The genus is quite large, comprising several hundred species that are native to warm temperate, subtropical and tropical regions throughout the world. Member species ...
'' native to Hawaii. The specific name is written in lower-case and may be followed by
subspecies names in
zoology or a variety of
infraspecific name
In botany, an infraspecific name is the scientific name for any taxon below the rank of species, i.e. an infraspecific taxon or infraspecies. (A "taxon", plural "taxa", is a group of organisms to be given a particular name.) The scientific names ...
s in
botany.
When the generic name is already known from context, it may be shortened to its initial letter, for example ''C. lupus'' in place of ''Canis lupus''. Where species are further subdivided, the generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, for the
Eurasian wolf
The Eurasian wolf (''Canis lupus lupus''), also known as the common wolf,Mech, L. David (1981), ''The Wolf: The Ecology and Behaviour of an Endangered Species'', University of Minnesota Press, p. 354, is a subspecies of grey wolf native to Euro ...
subspecies, or as a botanical example, . Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in
italics.
The scientific names of
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example, the virus species "
Salmonid herpesvirus 1", "
Salmonid herpesvirus 2" and "
Salmonid herpesvirus 3" are all within the genus ''
Salmonivirus'', however, the genus to which the species with the formal names "
Everglades virus" and "
Ross River virus" are assigned is ''
Alphavirus
''Alphavirus'' is a genus of RNA viruses, the sole genus in the ''Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses ...
''.
As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in the form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus ''Canis'' would be cited in full as "''Canis'' Linnaeus, 1758" (zoological usage), while ''Hibiscus'', also first established by
Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
but in 1753, is simply "''Hibiscus'' L." (botanical usage).
The type concept
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
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...
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 biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
in the former genus need to be reassessed.
Categories of generic name
In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with the
International Code of Zoological Nomenclature; the earliest such name for any taxon (for example, a genus) should then be selected as the "
valid" (i.e., current or accepted) name for the taxon in question.
Consequently, there will be more available names than valid names at any point in time, which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to the provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated.
According to "Glossary" section of the zoological Code, suppressed ''names'' (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for a taxon, however the names published in suppressed ''works'' are made unavailable via the relevant Opinion dealing with the work in question.
In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a
validly published name
In botanical nomenclature, a validly published name is a name that meets the requirements in the ''International Code of Nomenclature for algae, fungi, and plants'' for valid publication. Valid publication of a name represents the minimum require ...
. An invalidly published name is a ' or '; a rejected name is a ' or '; a later homonym of a validly published name is a ' or '; for a full list refer to the
''International Code of Nomenclature for algae, fungi, and plants'' and the work cited above by Hawksworth, 2010.
In place of the "valid taxon" in zoology, the nearest equivalent in botany is "
correct name
In botany, the correct name according to the International Code of Nomenclature for algae, fungi, and plants (ICN) is the one and only botanical name that is to be used for a particular taxon, when that taxon has a particular circumscription, posit ...
" or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split.
Prokaryote and
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
codes of nomenclature also exist which serve as a reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature".
An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for the taxon is termed a
synonym; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names.
A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for a long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the
World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus ''
Physeter'' Linnaeus, 1758, and 13 for the bivalve genus ''
Pecten'' O.F. Müller, 1776.
Identical names (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
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
Johann Friedrich Blumenbach (11 May 1752 – 22 January 1840) was a German physician, naturalist, physiologist, and anthropologist. He is considered to be a main founder of zoology and anthropology as comparative, scientific disciplines. He ...
published the replacement name ''Ornithorhynchus'' in 1800.
However, a genus in one
kingdom
Kingdom commonly refers to:
* A monarchy ruled by a king or queen
* Kingdom (biology), a category in biological taxonomy
Kingdom may also refer to:
Arts and media Television
* ''Kingdom'' (British TV series), a 2007 British television drama s ...
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 monkey
Night monkeys, also known as owl monkeys or douroucoulis (), are nocturnal New World monkeys of the genus ''Aotus'', the only member of the family Aotidae (). The genus comprises eleven species which are found across Panama and much of South Am ...
s;
* ''Oenanthe'' is the generic name of both
wheatear
The wheatears are passerine birds of the genus ''Oenanthe''. They were formerly considered to be members of the Thrush (bird), thrush family, Turdidae, but are now more commonly placed in the Old World flycatcher, flycatcher family, Muscicapid ...
s and
water dropwort
Water dropwort is a common name for several genera of plants and may refer to:
* ''Oenanthe'' (plant)
* ''Oxypolis
''Oxypolis'' is a small genus of North American flowering plants in the carrot family known as cowbane, water dropwort, dropwort ...
s;
* ''Prunella'' is the generic name of both
accentors and
self-heal
''Prunella'' is a genus of herbaceous plants in the family Lamiaceae, also known as self-heals, heal-all, or allheal for their use in herbal medicine.
Habitat
Most are native to Europe, Asia, and North Africa, but ''Prunella vulgaris'' (common ...
; and
* ''Proboscidea'' is the order of
elephants and the genus of
devil's claws.
* The name of the genus ''
Paramecia'' (an extinct red alga) is also the plural of the name of the genus ''
Paramecium
''
''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and marine environments and a ...
'' (which is in the SAR supergroup), which can also lead to confusion.
A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the
Interim Register of Marine and Nonmarine Genera (IRMNG).
Use in higher classifications
The
type genus
In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name.
Zoological nomenclature
According to the International Code of Zoological Nomenclature, "The name-bearing type of a nominal ...
forms the base for higher
taxonomic 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").
Numbers of accepted genera
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. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses
and prokaryotes, while for others there are compendia with no "official" standing such as ''
Index Fungorum
''Index Fungorum'' is an international project to index all formal names (scientific names) in the fungus kingdom. the project is based at the Royal Botanic Gardens, Kew, one of three partners along with Landcare Research and the Institute of M ...
'' for fungi, ''Index Nominum Algarum'' and
AlgaeBase
AlgaeBase is a global species database of information on all groups of algae, both marine and freshwater, as well as sea-grass.
History
AlgaeBase began in March 1996, founded by Michael Guiry. Text was copied from this source, which is avail ...
for algae, ''Index Nominum Genericorum'' and the
International Plant Names Index for plants in general, and ferns through angiosperms, respectively, and ''
Nomenclator Zoologicus'' 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:
*
Animalia: 239,093 accepted genus names (± 55,350)
*
Plantae: 28,724 (± 7,721)
*
Fungi: 10,468 (± 182)
*
Chromista
Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
: 11,114 (± 1,268)
*
Protozoa: 3,109 (± 1,206)
*
Bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
: 3,433 (± 115)
*
Archaea: 140 (± 0)
*
Virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es: 851 (± 0)
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
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s (class Insecta). Within Plantae,
Tracheophyta
Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They a ...
(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, also including genus names only (no species) for some groups.
Genus size
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. However, some insect genera such as the bee genera ''
Lasioglossum'' and ''
Andrena
''Andrena'' is a genus of bees in the family Andrenidae. With over 1,500 species, it is one of the largest genera of animals. It is a strongly monophyletic group that is difficult to split into more manageable divisions; currently, ''Andrena'' is ...
'' have over 1000 species each. The largest flowering plant genus, ''
Astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
'', 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 enormous, 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
There are over 56 genera of flowering plants estimated to contain at least 500 described species. The largest of these is currently the legume genus '' Astragalus'' (milk-vetches), with over 3,000 species.
The sizes of plant genera vary widely f ...
References
External links
Interim Register of Marine and Nonmarine Genera (IRMNG) includes an estimated 95% of published genus names (accepted and unaccepted) in all groups (semi-continuously updated)
''Nomenclator Zoologicus'': index of genus and subgenus names (accepted and unaccepted) in zoological nomenclature from 1758 to 2004
Index to Organism Names includes zoological taxon names at all ranks (including genera) as continuously indexed for the
''Zoological Record''
''Index Nominum Genericorum'' (ING) a compilation of generic names (accepted and unaccepted) published for organisms covered by the ICN: International Code of Nomenclature for Algae, Fungi, and Plants (semi-continuously updated)
LPSN – List of Prokaryotic names with Standing in Nomenclature includes all currently accepted Bacteria and Archaea genus names (continuously updated)
ICTV taxonomy releases latest and historical lists of accepted virus names compiled by the International Committee on Taxonomy of Viruses (ICTV), including all currently accepted virus genus names (updated via regular releases)
{{Taxonomic ranks
*01
Genus
Plant taxonomy
Zoological nomenclature
Bacterial nomenclature
Taxa named by Joseph Pitton de Tournefort