Genus

For other uses, seeGenus (disambiguation).

"Genera" redirects here. For the operating system, seeGenera (operating system).

The hierarchy ofbiological classification's eight majortaxonomic ranks.Afamilycontains one or more genera. Intermediate minor rankings are not shown.

Genus(/ˈdʒiːnəs/pl.:genera/ˈdʒɛnərə/) is ataxonomic rankabovespeciesand belowfamilyas used in thebiological classificationoflivingandfossilorganisms as well asviruses.Inbinomial nomenclature,the genus name forms the first part of the binomial species name for each species within the genus.

E.g.Panthera leo(lion) andPanthera onca(jaguar) are two species within the genusPanthera.Pantherais a genus within the familyFelidae.

The composition of a genus is determined bytaxonomists.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. monophyly– all descendants of an ancestraltaxonare grouped together (i.e.phylogeneticanalysis should clearly demonstrate both monophyly and validity as a separate lineage).
2. reasonable compactness – a genus should not be expanded needlessly.
3. distinctness – with respect to evolutionarily relevant criteria, i.e.ecology,morphology,orbiogeography;DNA sequencesare aconsequencerather than aconditionof diverging evolutionary lineages except in cases where they directly inhibitgene flow(e.g.postzygotic barriers).

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

Etymology

The term "genus" comes fromLatingenus,a noun formcognatewithgignere('to bear; to give birth to'). The Swedish taxonomistCarl Linnaeuspopularized its use in his 1753Species Plantarum,but the French botanistJoseph 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 thegeneric name;in modern style guides and science, it is always capitalised. It plays a fundamental role inbinomial nomenclature,the system of namingorganisms,where it is combined with the scientific name of aspecies:seeBotanical nameandSpecific name (zoology).

Use in nomenclature

Main articles:Binomial nomenclature,Taxonomy (biology),Author citation (zoology),andAuthor citation (botany)

The rules for thescientific namesoforganismsare laid down in thenomenclature codes,which allow each species a single unique name that, foranimals(includingprotists),plants(also includingalgaeandfungi) andprokaryotes(bacteriaandarchaea), isLatinand binomial in form; this contrasts withcommon or vernacular names,which are non-standardized, can be non-unique, and typically also vary by country and language of usage.

Except forviruses,the standard format for aspeciesname 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, thegray wolf's scientific name isCanis lupus,withCanis(Latinfor 'dog') being the generic name shared by the wolf's close relatives andlupus(Latin for 'wolf') being the specific name particular to the wolf. A botanical example would beHibiscus arnottianus,a particular species of the genusHibiscusnative to Hawaii. The specific name is written in lower-case and may be followed bysubspeciesnames inzoologyor a variety ofinfraspecific namesinbotany.

When the generic name is already known from context, it may be shortened to its initial letter, for example,C. lupusin place ofCanis lupus.Where species are further subdivided, the generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example,Canis lupus lupusfor theEurasian wolfsubspecies, or as a botanical example,Hibiscus arnottianusssp.immaculatus.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 initalics.

The scientific names ofvirusspecies 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 genusSalmonivirus;however, the genus to which the species with the formal names "Everglades virus"and"Ross River virus"are assigned isAlphavirus.

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 genusCaniswould be cited in full as "CanisLinnaeus, 1758 "(zoological usage), whileHibiscus,also first established byLinnaeusbut in 1753, is simply "HibiscusL. "(botanical usage).

The type concept

See also:Type genus,Type species,andType specimen

Each genus should have a designatedtype,although in practice there is a backlog of older names without one. In zoology, this is thetype species,and the generic name is permanently associated with thetype specimenof its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes ajunior synonymand the remainingtaxain 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 theInternational 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, suppressednames(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 suppressedworksare 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 avalidly published name.An invalidly published name is anomen invalidumornom. inval.;a rejected name is anomen rejiciendumornom. rej.;a later homonym of a validly published name is anomen illegitimumornom. illeg.;for a full list refer to theInternational Code of Nomenclature for algae, fungi, and plantsand 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.

Prokaryoteandviruscodes of nomenclature also exist which serve as a reference for designating currentlyaccepted 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".

Anavailable(zoological) orvalidly 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 asynonym;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, theWorld Register of Marine Speciespresently lists 8 genus-level synonyms for the sperm whale genusPhyseterLinnaeus, 1758,and 13 for the bivalve genusPectenO.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, theplatypusbelongs to the genusOrnithorhynchusalthoughGeorge Shawnamed itPlatypusin 1799 (these two names are thussynonyms).However, the namePlatypushad already been given to a group ofambrosia beetlesbyJohann Friedrich Wilhelm Herbstin 1793. A name that means two different things is ahomonym.Since beetles and platypuses are both members of the kingdom Animalia, the name could not be used for both.Johann Friedrich Blumenbachpublished the replacement nameOrnithorhynchusin 1800.

However, a genus in onekingdomis 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 theInternational Code of Zoological Nomenclatureand theInternational Code of Nomenclature for algae, fungi, and plants,there are some five thousand such names in use in more than one kingdom. For instance,

• Anurais the name of theorderof frogs but also is the name of anon-currentgenus of plants;
• Aotusis the generic name of bothgolden peasandnight monkeys;
• Oenantheis the generic name of bothwheatearsandwater dropworts;
• Prunellais the generic name of bothaccentorsandself-heal;and
• Proboscideais the order ofelephantsand the genus ofdevil's claws.
• The name of the genusParamecia(an extinct red alga) is also the plural of the name of the genusParamecium(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 theInterim Register of Marine and Nonmarine Genera(IRMNG).

Use in higher classifications

Thetype genusforms the base for highertaxonomicranks, such as the family nameCanidae( "Canids" ) based onCanis.However, this does not typically ascend more than one or two levels: theorderto which dogs and wolves belong isCarnivora( "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 virusesand prokaryotes,while for others there are compendia with no "official" standing such asIndex Fungorumfor fungi,Index Nominum AlgarumandAlgaeBasefor algae,Index Nominum Genericorumand theInternational Plant Names Indexfor plants in general, and ferns through angiosperms, respectively, andNomenclator Zoologicusand theIndex to Organism Namesfor zoological names.

Totals for both "all names" and estimates for "accepted names" as held in theInterim 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:

Estimated accepted genus totals by kingdom - based on Rees et al., 2020

• Animalia:239,093 accepted genus names (± 55,350)
• Plantae:28,724 (± 7,721)
• Fungi:10,468 (± 182)
• Chromista:11,114 (± 1,268)
• Protozoa:3,109 (± 1,206)
• Bacteria:3,433 (± 115)
• Archaea:140 (± 0)
• Viruses: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 isArthropoda,with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 areinsects(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 areangiosperms(superclass Angiospermae).

By comparison, the 2018 annual edition of theCatalogue of Life(estimated >90% complete, for extant species in the main) contains currently175,363 "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

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 theReptile 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. However, some insect genera such as the bee generaLasioglossumandAndrenahave 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 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 genusAnolishas 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

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 ZoologicusArchived2021-12-23 at theWayback Machine: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 theZoological 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 currentlyaccepted 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 currentlyaccepted virus genus names (updated via regular releases)