Genus: Difference between revisions

{{short description|Taxonomic rank useddirectly inabove the biological classification of living and fossil organisms, and virusesspecies}}

'''Genus''' ({{IPAc-en|ˈ|dʒ|iː|n|ə|s}} {{plural form}}: '''genera''' {{IPAc-en|ˈ|dʒ|ɛ|n|ər|ə|}}) is a [[taxonomic rank]] above [[species]] and below [[family (taxonomy)|family]] as used in the [[biological classification]] of [[extant taxon|living]] and [[fossil]] [[organism]]sorganisms as well as [[Virus classification#ICTV classification|virus]]es.<ref name = "ICTV">{{Cite web|url=https://ictv.global/taxonomy|title=ICTV Taxonomy|date=2017|access-date=May 29, 2018|publisher=[[International Committee on Taxonomy of Viruses]]|archive-date=March 20, 2020|archive-url=https://web.archive.org/web/20200320103754/https://talk.ictvonline.org/taxonomy/w/ictv|url-taxonomystatus=live}}</ref> In [[binomial nomenclature]], the genus name forms the first part of the binomial species name for each species within the genus.

The composition of a genus is determined by [[taxonomy (biology)|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,<ref>{{cite journal |last1=Sigward |first1=J. D. |first2=M. D. |last2=Sutton |first3=K. D. |last3=Bennett |title=How big is a genus? Towards a nomothetic systematics |journal=Zoological Journal of the Linnean Society |volume=183 |issue=2 |pages=237–252 |year=2018 |doi=10.1093/zoolinnean/zlx059 |url=https://pure.qub.ac.uk/portal/en/publications/how-big-is-a-genus-towards-a-nomothetic-systematics(939fc3e3-9067-4729-bd2a-23b32adfd556).html |doi-access=free |access-date=2018-12-22 |archive-date=2019-05-30 |archive-url=https://web.archive.org/web/20190530164327/https://pure.qub.ac.uk/portal/en/publications/how-big-is-a-genus-towards-a-nomothetic-systematics(939fc3e3-9067-4729-bd2a-23b32adfd556).html |url-status=live |hdl=10023/16213 |hdl-access=free }}</ref><ref>{{cite journal |last1=Gill |first1=F. B. |first2=B. |last2=Slikas |first3=F. H. |last3=Sheldon |title=Phylogeny of titmice (Paridae): II. Species relationships based on sequences of the mitochondrial cytochrome-b gene |journal=Auk |volume=122 |issue=1 |pages=121–143 |year=2005 |doi=10.1642/0004-8038(2005)122[0121:POTPIS]2.0.CO;2 |s2cid=86067032 }}</ref> 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. [[Phylogenetics|phylogenetic]] analysis should clearly demonstrate both monophyly and validity as a separate lineage).

# distinctness – with respect to evolutionarily relevant criteria, i.e. [[ecology]], [[Morphology (biology)|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 barrier]]s).

The term "genus" comes from the [[Greek language|GreekLatin]] [[wikt:γένος{{Wikt-lang|γένος]]la|genus}}, a noun form [[cognate]] with ''{{lang|la|[[wikt:gigno|gignere]]}}'' ('to bear; to give birth to'). The Swedish taxonomist [[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".<ref>{{cite book |last=Stuessy |first=T. F. |yearurl=2009https://books.google.com/books?id=W8CrAgAAQBAJ&pg=PA42 |title=Plant Taxonomy: The Systematic Evaluation of Comparative Data |publisher=[[Columbia University Press]] |year=2009 |isbn=9780231147125 |edition=2nd |location=[[New York, New York]], US |publisherpage=[[Columbia42 University Press]]|access-date=2023-03-19 |pagearchive-date=422023-04-06 |isbnarchive-url=9780231147125https://web.archive.org/web/20230406152109/https://books.google.com/books?id=W8CrAgAAQBAJ&pg=PA42 |editionurl-status=2ndlive }}</ref>

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]]s, where it is combined with the scientific name of a [[species]]: see [[Botanical name]] and [[Specific name (zoology)]].<ref>{{cncite book |author=International Commission on Zoological Nomenclature |author-link= |date=September1999 |title=International Code of Zoological Nomenclature |url=https://www.iczn.org/the-code/the-code-online/ |location=London |publisher=The International Trust for Zoological Nomenclature |page= |isbn=0-85301-006-4 |access-date=2023-11-10 |archive-date=2021-09-03 |archive-url=https://web.archive.org/web/20210903062842/https://www.iczn.org/the-code/the-code-online/ |url-status=live }}</ref><ref>{{cite web |url=http://www.iapt-taxon.org/nomen/main.php?page=art3 |title=International Code of Nomenclature for algae, fungi, and plants – Melbourne Code |date=2012 |website=IAPT-Taxon.org |access-date=2023-11-10 |archive-date=2020-10-10 |archive-url=https://web.archive.org/web/20201010230658/https://www.iapt-taxon.org/nomen/main.php?page=art3 |url-status=live 2022}}</ref>

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, {{nowrap|''{{lang|la|Canis lupus lupus}}''}} for the [[Eurasian wolf]] subspecies, or as a botanical example, {{nowrap|''{{lang|la|Hibiscus arnottianus}}'' ssp. ''{{lang|la|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 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]]''.

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.<ref name="Hawksworth2010">{{cite book|author=D. L. Hawksworth|title=Terms Used in Bionomenclature: The Naming of Organisms and Plant Communities : Including Terms Used in Botanical, Cultivated Plant, Phylogenetic, Phytosociological, Prokaryote (bacteriological), Virus, and Zoological Nomenclature|url=https://books.google.com/books?id=Qky7_6-UcQQC&pg=PA10|year=2010|publisher=GBIF|isbn=978-87-92020-09-3|pages=1–215}}</ref> 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]]. An invalidly published name is a ''{{Lang|latla|nomen invalidum}}'' or ''{{Lang|latla|nom. inval.}}''; a rejected name is a ''{{Lang|latla|nomen rejiciendum}}'' or ''{{Lang|latla|nom. rej.}}''; a later homonym of a validly published name is a ''{{Lang|latla|nomen illegitimum}}'' or ''{{Lang|latla|nom. illeg.}}''; for a full list refer to the ''[[International Code of Nomenclature for algae, fungi, and plants|]]''International Code of Nomenclature for algae, fungi, and plants'']] and the work cited above by Hawksworth, 2010.<ref name="Hawksworth2010" /> 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{{When|date=August 2023}} 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".

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,<ref>{{Cite web|url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=137032|title=WoRMS - World Register of Marine Species - Physeter Linnaeus, 1758|website=www.marinespecies.org|access-date=2018-06-02|archive-date=2017-07-09|archive-url=https://web.archive.org/web/20170709213325/http://www.marinespecies.org/aphia.php?p=taxdetails&id=137032|url-status=live}}</ref> and 13 for the bivalve genus ''[[Pecten (bivalve)|Pecten]]'' O.F. Müller, 1776.<ref>{{Cite web|url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=138323|title=WoRMS - World Register of Marine Species - Pecten O. F. Müller, 1776|website=www.marinespecies.org|access-date=2018-06-02|archive-date=2018-08-10|archive-url=https://web.archive.org/web/20180810174658/http://www.marinespecies.org/aphia.php?p=taxdetails|url-status=live}}</ref>

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).<ref name ="IRMNG">{{Cite web|url=http://www.irmng.org/homonyms.php|title=IRMNG: Interim Register of Marine and Nonmarine Genera|website=www.irmng.org|access-date=2016-11-17|archive-date=2016-11-17|archive-url=https://web.archive.org/web/20161117212132/http://www.irmng.org/homonyms.php|url-status=live}}</ref>

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.<ref>{{cite journal |last1=Rees |first1=Tony |last2=Vandepitte |first2=Leen |last3=Vanhoorne |first3=Bart |last4=Decock |first4=Wim |title=All genera of the world: an overview and estimates based on the March 2020 release of the Interim Register of Marine and Nonmarine Genera (IRMNG) |journal=Megataxa |volume=1 |pages=123–140 |year=2020 |issue=2 |url=https://www.mapress.com/j/mt/article/view/megataxa.1.2.3/39250 |doi=10.11646/megataxa.1.2.3 |doi-access=free |access-date=2020-04-02 |archive-date=2021-03-22 |archive-url=https://web.archive.org/web/20210322091308/https://www.mapress.com/j/mt/article/view/megataxa.1.2.3/39250 |url-status=live }}</ref> "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses<ref name = "ICTV" /> and prokaryotes,<ref>{{Cite web|url=http://www.bacterio.net/|title=LPSN - List of Prokaryotic names with Standing in Nomenclature|website= bacterio.net|access-date=2018-06-01|archive-date=2022-04-01|archive-url=https://web.archive.org/web/20220401092957/https://www.bacterio.net/|url-status=live}}</ref> while for others there are compendia with no "official" standing such as ''[[Index Fungorum]]'' for fungi,<ref>{{Cite web|url=http://www.indexfungorum.org/|title=Index Fungorum Home Page|website= indexfungorum.org|access-date=2018-06-01|archive-date=2015-02-05|archive-url=https://web.archive.org/web/20150205221807/http://www.indexfungorum.org/|url-status=live}}</ref> ''Index Nominum Algarum''<ref>{{Cite web|url=https://ucjeps.berkeley.edu/ina/|title=Index Nominum Algarum: names of algae|website=Jepson Herbarium - University of California, Berkeley |access-date=2020-09-06|archive-date=2020-08-07|archive-url=https://web.archive.org/web/20200807001456/https://ucjeps.berkeley.edu/ina/|url-status=live}}</ref> and [[AlgaeBase]]<ref>{{Cite web|url=https://www.algaebase.org/|title=Algaebase :: Listing the World's Algae|website=algaebase.org|access-date=2020-09-06|archive-date=2020-08-29|archive-url=https://web.archive.org/web/20200829085615/https://www.algaebase.org/|url-status=live}}</ref> for algae, ''Index Nominum Genericorum''<ref>{{Cite web|url=https://naturalhistory2.si.edu/botany/ing/|title=Index Nominum Genericorum (ING), Botany, |website=Smithsonian InstitutionNational Museum of Natural History |websiteaccess-date=naturalhistory22019-06-07|archive-date=2016-03-03|archive-url=https://web.archive.org/web/20160303234638/http://botany.si.edu/ing/INGsearch.cfm?SearchWord=eggersia|url-status=live}}</ref> and the [[International Plant Names Index]]<ref>{{Cite web|url=https://www.ipni.org/|title=International Plant Names Index|website= ipni.org|access-date=2020-09-06|archive-date=2020-05-02|archive-url=https://web.archive.org/web/20200502112641/https://www.ipni.org/|url-status=live}}</ref> for plants in general, and ferns through angiosperms, respectively, and ''[[Nomenclator Zoologicus]]''<ref>{{Cite web|url=http://ubio.org/NomenclatorZoologicus/|title=Nomenclator Zoologicus|website=uBio |access-date=2018-02-24|archive-date=2021-12-23|archive-url=https://web.archive.org/web/20211223191732/http://ubio.org/NomenclatorZoologicus/|url-status=dead}}</ref> and the [[Index to Organism Names]] for zoological names.

By comparison, the 2018 annual edition of the [[Catalogue of Life]] (estimated >90% complete, for extant species in the main) contains currently{{When|date=August 2023}} 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species,<ref>{{Cite web|url=http://www.catalogueoflife.org/annual-checklist/2018/info/ac|title=Catalogue of Life - 2018 Annual Checklist|website=Catalogue :of 2018Life Annual Checklist|websiteaccess-date=2018-07-07|archive-date=2020-11-11|archive-url=https://web.archive.org/web/20201111212241/http://www.catalogueoflife.org/annual-checklist/2018/info/ac|url-status=live}}</ref> also including genus names only (no species) for some groups.

The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) [[reptile]]s, 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 (plant)|Astragalus]]'', contains over 3,000 species.<ref name="Frodin">{{cite journal |last=Frodin |first=David G. |year=2004 |title=History and concepts of big plant genera |journal=[[Taxon (journal)|Taxon]] |volume=53 |issue=3 |pages=753–776 |jstor=4135449 |doi=10.2307/4135449}}</ref>

* [http://www.bacterio.net/ LPSN – List of Prokaryotic names with Standing in Nomenclature]: includes all currently{{When|date=August 2023}} accepted Bacteria and Archaea genus names (continuously updated)

* [https://talkictv.ictvonline.orgglobal/taxonomy/p/taxonomy_releases ICTV taxonomy releases]: latest and historical lists of accepted virus names compiled by the International Committee on Taxonomy of Viruses (ICTV), including all currently{{When|date=August 2023}} accepted virus genus names (updated via regular releases)