In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, order, class, phylum, kingdom, domain, etc.
A given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms and groups of organisms related to each other through inheritance of traits or features from common ancestors. The rank of any species and the description of its genus is basic; which means that to identify a particular organism, it is usually not necessary to specify ranks other than these first two.
Consider a particular species, the red fox, Vulpes vulpes: the next rank above, the genus Vulpes, comprises all the "true" foxes. Their closest relatives are in the immediately higher rank, the family Canidae, which includes dogs, wolves, jackals, and all foxes; the next higher rank, the order Carnivora, includes caniforms (bears, seals, weasels, skunks, raccoons and all those mentioned above), and feliforms (cats, civets, hyenas, mongooses). Carnivorans are one group of the hairy, warm-blooded, nursing members of the class Mammalia, which are classified among animals with backbones in the phylum Chordata, and with them among all animals in the kingdom Animalia. Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya.
The International Code of Zoological Nomenclature defines rank as: "The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily)."
In his landmark publications, such as the Systema Naturae, Carl Linnaeus used a ranking scale limited to: kingdom, class, order, genus, species, and one rank below species. Today, nomenclature is regulated by the nomenclature codes. There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, species. In addition, domain (proposed by Carl Woese) is now widely used as a fundamental rank, although it is not mentioned in any of the nomenclature codes, and is a synonym for dominion (lat. dominium), introduced by Moore in 1974.
|Main taxonomic ranks|
|phylum||phylum (in zoology)|
A taxon is usually assigned a rank when it is given its formal name. The basic ranks are species and genus. When an organism is given a species name it is assigned to a genus, and the genus name is part of the species name.
The species name is also called a binomial, that is, a two-term name. For example, the zoological name for the human species is Homo sapiens. This is usually italicized in print and underlined when italics are not available. In this case, Homo is the generic name and it is capitalized; sapiens indicates the species and it is not capitalized.
There are definitions of the following taxonomic ranks in the International Code of Zoological Nomenclature: superfamily, family, subfamily, tribe, subtribe, genus, subgenus, species, subspecies.
The International Code of Zoological Nomenclature divides names into "family-group names", "genus-group names" and "species-group names". The Code explicitly mentions the following ranks for these categories:
The rules in the Code apply to the ranks of superfamily to subspecies, and only to some extent to those above the rank of superfamily. Among "genus-group names" and "species-group names" no further ranks are officially allowed. Zoologists sometimes use additional terms such as species group, species subgroup, species complex and superspecies for convenience as extra, but unofficial, ranks between the subgenus and species levels in taxa with many species, e.g. the genus Drosophila. (Note the potentially confusing use of "species group" as both a category of ranks as well as an unofficial rank itself.)
At higher ranks (family and above) a lower level may be denoted by adding the prefix "infra", meaning lower, to the rank. For example, infraorder (below suborder) or infrafamily (below subfamily).
According to Art 3.1 of the International Code of Nomenclature for algae, fungi, and plants (ICN) the most important ranks of taxa are: kingdom, division or phylum, class, order, family, genus, and species. According to Art 4.1 the secondary ranks of taxa are tribe, section, series, variety and form. There is an indeterminate number of ranks. The ICN explicitly mentions:
division or phylum (divisio, phylum)
There are definitions of the following taxonomic categories in the International Code of Nomenclature for Cultivated Plants: cultivar group, cultivar, grex.
The rules in the ICN apply primarily to the ranks of family and below, and only to some extent to those above the rank of family. Also see descriptive botanical names.
Taxa at the rank of genus and above have a botanical name in one part (unitary name); those at the rank of species and above (but below genus) have a botanical name in two parts (binary name); all taxa below the rank of species have a botanical name in three parts (an infraspecific name). To indicate the rank of the infraspecific name, a "connecting term" is needed. Thus Poa secunda subsp. juncifolia, where "subsp." is an abbreviation for "subspecies", is the name of a subspecies of Poa secunda.
Hybrids can be specified either by a "hybrid formula" that specifies the parentage, or may be given a name. For hybrids receiving a hybrid name, the same ranks apply, prefixed with notho (Greek: 'bastard'), with nothogenus as the highest permitted rank.
If a different term for the rank was used in an old publication, but the intention is clear, botanical nomenclature specifies certain substitutions:
Classifications of five species follow: the fruit fly familiar in genetics laboratories (Drosophila melanogaster), humans (Homo sapiens), the peas used by Gregor Mendel in his discovery of genetics (Pisum sativum), the "fly agaric" mushroom Amanita muscaria, and the bacterium Escherichia coli. The eight major ranks are given in bold; a selection of minor ranks are given as well.
|Rank||Fruit fly||Human||Pea||Fly agaric||E. coli|
|Phylum or Division||Arthropoda||Chordata||Magnoliophyta (Tracheophyta)||Basidiomycota||Proteobacteria|
|Subphylum or subdivision||Hexapoda||Vertebrata||Magnoliophytina (Euphyllophytina)||Agaricomycotina|
|Species||D. melanogaster||H. sapiens||P. sativum||A. muscaria||E. coli|
Taxa above the genus level are often given names based on the type genus, with a standard termination. The terminations used in forming these names depend on the kingdom (and sometimes the phylum and class) as set out in the table below.
Pronunciations given are the most Anglicized. More Latinate pronunciations are also common, particularly /ɑː/ rather than /eɪ/ for stressed a.
|Division/Phylum||-phyta /ˈfaɪtə/||-phyta /ˈfaɪtə/||-mycota /maɪˈkoʊtə/|
|Subdivision/Subphylum||-phytina /fɪˈtaɪnə/||-phytina /fɪˈtaɪnə/||-mycotina /maɪkoʊˈtaɪnə/|
|Class||-ia /iə/||-opsida /ˈɒpsɪdə/||-phyceae /ˈfaɪʃi/||-mycetes /maɪˈsiːtiːz/|
|Subclass||-idae /ɪdi/||-phycidae /ˈfɪsɪdi/||-mycetidae /maɪˈsɛtɪdi/|
|Superfamily||-acea /ˈeɪʃə/||-oidea /ˈɔɪdiə/|
|Family||-aceae /ˈeɪʃi/||-idae /ɪdi/|
|Subfamily||-oideae /ˈɔɪdii/||-inae /ˈaɪni/|
|Tribe||-eae /ii/||-ini /ˈaɪnaɪ/|
|Subtribe||-inae /ˈaɪni/||-ina /ˈaɪnə/|
|Infratribe||-ad /æd/ or -iti /ˈaɪti/|
There is an indeterminate number of ranks, as a taxonomist may invent a new rank at will, at any time, if they feel this is necessary. In doing so, there are some restrictions, which will vary with the nomenclature code which applies.
The following is an artificial synthesis, solely for purposes of demonstration of relative rank (but see notes), from most general to most specific:
Ranks are assigned based on subjective dissimilarity, and do not fully reflect the gradational nature of variation within nature. In most cases, higher taxonomic groupings arise further back in time: not because the rate of diversification was higher in the past, but because each subsequent diversification event results in an increase of diversity and thus increases the taxonomic rank assigned by present-day taxonomists. Furthermore, some groups have many described species not because they are more diverse than other species, but because they are more easily sampled and studied than other group.
Of these many ranks, the most basic is species. However, this is not to say that a taxon at any other rank may not be sharply defined, or that any species is guaranteed to be sharply defined. It varies from case to case. Ideally, a taxon is intended to represent a clade, that is, the phylogeny of the organisms under discussion, but this is not a requirement.
A classification in which all taxa have formal ranks cannot adequately reflect knowledge about phylogeny. Since taxon names are dependent on ranks in traditional Linnaean systems of classification, taxa without ranks cannot be given names. Alternative approaches, such as using circumscriptional names, avoid this problem.
There are no rules for how many species should make a genus, a family, or any other higher taxon (that is, a taxon in a category above the species level). It should be a natural group (that is, non-artificial, non-polyphyletic), as judged by a biologist, using all the information available to them. Equally ranked higher taxa in different phyla are not necessarily equivalent (e.g., it is incorrect to assume that families of insects are in some way evolutionarily comparable to families of mollusks). For animals, at least the phylum rank is usually associated with a certain body plan, which is also, however, an arbitrary criterion.
In biological classification, class (Latin: classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order.Domain (biology)
In biological taxonomy, a domain [/də(ʊ)ˈmeɪn/] (Latin: regio), also superkingdom or empire, is the highest taxonomic rank of organisms in the three-domain system of taxonomy designed by Carl Woese et.al. in 1990.
According to this system, the tree of life consists of three domains: Archaea, Bacteria, and Eukarya. The first two are all prokaryotic microorganisms, or single-celled organisms whose cells have no nucleus. All life that has a nucleus and membrane-bound organelles, and multicellular organisms, is included in the Eukarya.Genus
A genus (, pl. genera ) is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, 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.
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 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; and
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. postzygotic barriers).Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.Interim Register of Marine and Nonmarine Genera
The Interim Register of Marine and Nonmarine Genera (IRMNG) is a taxonomic database containing the scientific names of the genus, species, and higher ranks of many plants, animals and other kingdoms, both living and extinct, within a standardized taxonomic hierarchy, with associated machine-readable information on habitat (e.g. marine/nonmarine) and extant/fossil status for the majority of entries. The database aspires to provide complete coverage of both accepted and unaccepted genus names across all kingdoms, with a subset only of species names included as a lower priority. In its March 2019 release, IRMNG contained 490,095 genus names, of which 236,514 were listed as "accepted", 120,194 "unaccepted", 7,391 of "other" status i.e. interim unpublished, nomen dubium, nomen nudum, taxon inquirendum or temporary name, and 125,996 as "uncertain" (unassessed for taxonomic status at this time). The data originate from a range of (frequently domain-specific) print, online and database sources, and are reorganised into a common data structure to support a variety of online queries, generation of individual taxon pages, and bulk data supply to other biodiversity informatics projects. IRMNG content can be queried and displayed freely via the web, and download files of the data down to the taxonomic rank of genus as at specific dates are available in the Darwin Core Archive (DwC-A) format.
The data include homonyms (with their authorities), including both available (validly published) and selected unavailable names.IRMNG was initiated in 2006 by the Ocean Biogeographic Information System (OBIS) Australia at CSIRO Marine and Atmospheric Research, and subsequently has been hosted by the Flanders Marine Institute (VLIZ) from 2016 onwards. VLIZ also hosts the World Register of Marine Species (WoRMS), using a common infrastructure.Content from IRMNG is used by several global Biodiversity Informatics projects including Open Tree of Life, the Global Biodiversity Information Facility (GBIF), and the Encyclopedia of Life (EOL), in addition to others including the Atlas of Living Australia and the Global Names Architecture (GNA)'s Global Names Resolver. From 2018 onwards, IRMNG data are also being used to populate the taxonomic hierarchy and provide generic names for a range of taxa in the areas of protists (kingdoms Protozoa and Chromista) and plant algae (Charophyta, Chlorophyta, Glaucophyta and Rhodophyta) in the Catalogue of Life. IRMNG identifiers have also been associated with numerous Wikipedia taxon pages, based on content harvested from IRMNG and stored in Wikidata.IRMNG was initiated and designed by Tony Rees. For his work on this and other projects, GBIF awarded him the 2014 Ebbe Nielsen Prize. The citation said, in part:
IRMNG in particular has been a tool of enormous importance to GBIF and others in supplying much of the detail for a global taxonomic classification of all life and as high-value taxon trait data in a form which can readily be reused in data validation and to enhance species pages.
IRMNG is currently (2019) managed and curated by Rees, with assistance from the VLIZ team.Legion (taxonomy)
The legion, in biological classification, is a non-obligatory taxonomic rank within the Linnaean hierarchy sometimes used in zoology.Order (biology)
In biological classification, the order (Latin: ordo) is
a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family. An immediately higher rank, superorder, may be added directly above order, while suborder would be a lower rank.
a taxonomic unit, a taxon, in that rank. In that case the plural is orders (Latin ordines).Example: All owls belong to the order StrigiformesWhat does and does not belong to each order is determined by a taxonomist, as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognised only rarely.For some groups of organisms, consistent suffixes are used to denote that the rank is an order. The Latin suffix -(i)formes meaning "having the form of" is used for the scientific name of orders of birds and fishes, but not for those of mammals and invertebrates. The suffix -ales is for the name of orders of plants, fungi, and algae.Polecat
Polecat is a common name for mammals in the order Carnivora and subfamilies Galictinae and Mustelinae. Polecats do not form a single taxonomic rank (i.e., clade); the name is applied to several species with broad similarities (including having a dark mask-like marking across the face) to European polecats, the only species native to the British Isles.
In the United States, the term polecat is sometimes applied to the black-footed ferret, a native member of the Mustelinae, and (loosely) to skunks, which are only distantly related.
Despite the name, polecats, being various caniform mustelids, are more closely related to dogs than cats, which is why they belong to the suborder Caniformia.
In Canada, the term polecat is sometimes applied to electric utility linemen.Rosales
Rosales is an order of flowering plants. It is sister to a clade consisting of Fagales and Cucurbitales. It contains about 7700 species, distributed into about 260 genera. Rosales comprise nine families, the type family being the rose family, Rosaceae. The largest of these families are Rosaceae (90/2500) and Urticaceae (54/2600). The order Rosales is divided into three clades that have never been assigned a taxonomic rank. The basal clade consists of the family Rosaceae; another clade consists of four families, including Rhamnaceae; and the third clade consists of the four urticalean families.The order Rosales is strongly supported as monophyletic in phylogenetic analyses of DNA sequences, such as those carried out by members of the Angiosperm Phylogeny Group. In their APG III system of plant classification, they defined Rosales as consisting of the nine families listed in the box on the right. The relationships of these families were uncertain until 2011, when they were resolved in a molecular phylogenetic study based on two nuclear genes and ten chloroplast genes.Well-known members of Rosales include: roses, strawberries, blackberries and raspberries, apples and pears, plums, peaches and apricots, almonds, rowan and hawthorn, jujube, elms, banyans, figs, mulberries, breadfruit, nettles, hops, and cannabis.Section (biology)
In biology a section (Latin: Sectio) is a taxonomic rank that is applied differently between botany and zoology.Section (botany)
In botany, a section (Latin: sectio) is a taxonomic rank below the genus, but above the species. The subgenus, if present, is higher than the section, and the rank of series, if present, is below the section. Sections may in turn be divided into subsections.Sections are typically used to help organise very large genera, which may have hundreds of species. A botanist wanting to distinguish groups of species may prefer to create a taxon at the rank of section or series to avoid making new combinations, i.e. many new binomial names for the species involved.Examples:
Lilium section Martagon Rchb. are the Turks' cap lilies
Plagiochila aerea Taylor is the type species of Plagiochila sect. BursataeSeries (botany)
In botany and plant taxonomy, a series is a subdivision of a genus, a taxonomic rank below that of section (and subsection) but above that of species.Sections and/or series are typically used to help organize very large genera, which may have hundreds of species.Subfamily
In biological classification, a subfamily (Latin: subfamilia, plural subfamiliae) is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoological names with "-inae".Subgenus
In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus.
In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the tiger cowry of the Indo-Pacific, Cypraea (Cypraea) tigris Linnaeus, which belongs to the subgenus Cypraea of the genus Cypraea. However, it is not mandatory, or even customary, when giving the name of a species, to include the subgeneric name.
In the International Code of Nomenclature for algae, fungi, and plants, the subgenus is one of the possible subdivisions of a genus. There is no limit to the number of divisions that are permitted within a genus by adding the prefix "sub-" or in other ways as long as no confusion can result. The secondary ranks of section and series are subordinate to subgenus.In zoological nomenclature, when a genus is split into subgenus, the originally described population is retained as the "nominotypical subgenus" or "nominate subgenus", which repeats the same name as the genus. For example, Panthera (Panthera) pardus, a leopard.Subphylum
In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum.
The taxonomic rank of "subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy.Subspecies
In biological classification, the term subspecies refers to one of two or more populations of a species living in different subdivisions of the species' range and varying from one another by morphological characteristics.
A single subspecies cannot be recognized independently: a species is either recognized as having no subspecies at all or at least two, including any that are extinct. The term is abbreviated subsp. in botany and bacteriology, ssp. in zoology. The plural is the same as the singular: subspecies.
In zoology, under the International Code of Zoological Nomenclature, the subspecies is the only taxonomic rank below that of species that can receive a name. In botany and mycology, under the International Code of Nomenclature for algae, fungi, and plants, other infraspecific ranks, such as variety, may be named. In bacteriology and virology, under standard bacterial nomenclature and virus nomenclature, there are recommendations but not strict requirements for recognizing other important infraspecific ranks.
A taxonomist decides whether to recognize a subspecies or not. A common criterion for recognizing two distinct populations as subspecies rather than full species is the ability of them to interbreed without a fitness penalty. In the wild, subspecies do not interbreed due to geographic isolation or sexual selection. The differences between subspecies are usually less distinct than the differences between species.Tribe (biology)
In biology, a tribe is a taxonomic rank above genus, but below family and subfamily. It is sometimes subdivided into subtribes.
In zoology, the standard ending for the name of a zoological tribe is "-ini". Examples include the tribes Caprini (goat-antelopes), Hominini (hominins), Bombini (bumblebees), and Thunnini (tunas). The tribe Hominini is divided into subtribes by some scientists; subtribe Hominina then comprises "humans". The standard ending for the name of a zoological subtribe is "-ina".
In botany, the standard ending for the name of a botanical tribe is "-eae". Examples include the tribes Acalypheae and Hyacintheae. The tribe Hyacintheae is divided into subtribes, including the subtribe Massoniinae. The standard ending for the name of a botanical subtribe is "-inae".
In bacteriology, the form of tribe names is as in botany, e.g., Pseudomonadeae, based on the genus name Pseudomonas.Variety (botany)
In botanical nomenclature, variety (abbreviated var.; in Latin: varietas) is a taxonomic rank below that of species and subspecies, but above that of form. As such, it gets a three-part infraspecific name. It is sometimes recommended that the subspecies rank should be used to recognize geographic distinctiveness, whereas the variety rank is appropriate if the taxon is seen throughout the geographic range of the species.