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Genus (plural genera) is a
taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
used in the biological classification of living and
fossil A fossil (from Classical Latin: , literally "obtained by digging") 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 anima ...
organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline of life forms, life form". Organ ...
s as well as
virus A virus is a submicroscopic infectious agent that Viral replication, replicates only inside the living Cell (biology), cells of an organism. Viruses infect all types of life forms, from animals and plants to microorganisms, including bacte ...
es, in
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Developmenta ...
. In the hierarchy of biological classification, genus comes above
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...
and below
family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well-being of its members an ...
. In
binomial nomenclature In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species In biology, a species is the basic unit of biological classi ...
, the genus name forms the first part of the binomial species name for each species within the genus. :E.g. '' Panthera leo'' (lion) and '''' (jaguar) are two species within the genus ''
Panthera ''Panthera'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer t ...
''. ''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 Image:Monophyly, paraphyly, polyphyly.png, 300px, A cladogram of the primates, showing a ''monophyletic'' taxon: ''the simians'' (in yellow); a ''paraphyletic'' taxon: ''the prosimians'' (in cyan, including the red patch); and a ''polyphyletic'' ...
– all descendants of an ancestral
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
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 Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Topics of interest include the biodiversity, di ...
, morphology, or biogeography; DNA sequences are a ''consequence'' rather than a ''condition'' of diverging evolutionary lineages except in cases where they directly wikt:inhibit, inhibit gene flow (e.g. postzygotic barriers). Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.


Etymology

The term "genus" comes from the Latin ' ('origin, type, group, race, family'), a noun form Cognate (etymology), cognate with ' ('to bear; to give birth to'). Carl Linnaeus, 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 (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 In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species In biology, a species is the basic unit of biological classi ...
, the system of naming organisms, where it is combined with the scientific name of a
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...
: see Specific name (botany) and Specific name (zoology).


Use in nomenclature

The rules for the scientific names of organisms 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 and Archaea), is Latin and binomial in form; this contrasts with common name, common or vernacular names, which are non-standardized, can be non-unique, and typically also vary by country and language of usage. Except for Virus classification, viruses, the standard format for a
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...
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'' (Latin 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'' 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 (botany), infraspecific names 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 domestic dog (when considered a subspecies of the gray wolf) in zoology, 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 Italic type, italics. The scientific names of virus 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''. 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 Carl Linnaeus, Linnaeus but in 1753, is simply "''Hibiscus'' L." (botanical usage).


The type concept

Each genus should have a designated type (biology), 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, taxa 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 and not otherwise suppressed by subsequent decisions of the International Commission on Zoological Nomenclature (ICZN); the earliest such name for any taxon (for example, a genus) should then be selected as the "valid name (zoology), 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, or have subsequently been suppressed, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name. An invalidly published name is a ''nomen invalidum'' or ''nom. inval.''; a rejected name is a ''nomen rejiciendum'' or ''nom. rej.''; a later homonym of a validly published name is a ''nomen illegitimum'' or ''nom. illeg.''; for a full list refer the International Code of Nomenclature for algae, fungi, and plants (ICNafp) and the work cited above by Hawksworth, 2010. In place of the "valid taxon" in zoology, the nearest equivalent in botany is "correct name" 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. International Code of Nomenclature of Prokaryotes, Prokaryote and International Committee on Taxonomy of Viruses, virus 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 (taxonomy), 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 (bivalve), 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 published the replacement name ''Ornithorhynchus'' in 1800. However, a genus in one kingdom (biology), 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 (frog), Anura'' is the name of the order (biology), order of frogs but also is the name of a synonym (botany), non-current genus of plants; * ''Aotus'' is the generic name of both Aotus (pea), 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 Proboscidea (plant), devil's claws. * The name of the genus ''Paramecia (alga), Paramecia'' (an extinct red alga) 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 (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 forms the base for higher Taxonomy (biology), 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 (biology), 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'' for Fungi, ''Index Nominum Algarum'' and AlgaeBase 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 (http://www.organismnames.com/) 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 accepted genus names (± 7,721) * Fungi: 10,468 accepted genus names (± 182) * Chromista: 11,114 accepted genus names (± 1,268) * Protozoa: 3,109 accepted genus names (± 1,206) * Bacteria: 3,433 accepted genus names (± 115) * Archaea: 140 accepted genus names (± 0) * Viruses: 851 accepted genus names (± 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 insects (class Insecta). Within Plantae, Tracheophyta (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'' have over 1000 species each. The largest flowering plant genus, ''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.


See also

* List of the largest genera of flowering plants


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 The Zoological Record, ''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) {{DEFAULTSORT:rank17 Genera, *01 Botanical nomenclature, Genus Plant taxonomy, 1rank17 Zoological nomenclature Bacterial nomenclature Taxa named by Joseph Pitton de Tournefort