![Taxonomic Rank Graph](https://upload.wikimedia.org/wikipedia/commons/7/71/Taxonomic_Rank_Graph.svg)
In
biological classification
In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...
, taxonomic rank is the relative level of a group of organisms (a
taxon
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 an ancestral or hereditary
hierarchy
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
. A common system consists of
species
In biology, a species is the basic unit of 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 individuals of the appropriate s ...
,
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
,
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
,
order,
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
,
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
,
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 ...
,
domain
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
* Do ...
. While older approaches to taxonomic classification were phenomenological, forming groups on the basis of similarities in appearance, organic structure and behaviour, methods based on
genetic analysis
Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research, and these are also considered parts of ...
have opened the road to
cladistics
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
.
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
The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the Order (biology), order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe ...
, ''Vulpes vulpes'': the
specific name or specific epithet ''vulpes'' (small ''v'') identifies a particular species in the genus ''Vulpes'' (capital ''V'') which comprises all the "true" foxes. Their close relatives are all in the family
Canidae
Canidae (; from Latin, ''canis'', "dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found within th ...
, which includes dogs, wolves, jackals, and all foxes; the next higher major rank, the order
Carnivora
Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...
, includes
caniforms
Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include dogs (wolves, foxes, etc.), bears, raccoons, and mustelids. The Pinnipedia (seals, walruses and sea lions) are also assigned to this group. ...
(bears, seals, weasels, skunks, raccoons and all those mentioned above), and
feliforms
Feliformia is a suborder within the order Carnivora consisting of "cat-like" carnivorans, including cats (large and small), hyenas, mongooses, viverrids, and related taxa. Feliformia stands in contrast to the other suborder of Carnivora, Canifor ...
(cats, civets, hyenas, mongooses). Carnivorans are one group of the hairy, warm-blooded, nursing members of the class
Mammalia
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
, which are classified among animals with backbones in the phylum
Chordata
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fiv ...
, and with them among all animals in the kingdom
Animalia
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
. Finally, at the highest rank all of these are grouped together with all other organisms possessing
cell nuclei
The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...
in the domain
Eukarya
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
.
The ''
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...
'' defines ''rank'' as: "The level, for nomenclatural purposes, of a
taxon
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 a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily)."
Main ranks
In his landmark publications, such as the ''
Systema Naturae
' (originally in Latin written ' with the ligature æ) is one of the major works of the Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the system, now known as binomial nomen ...
'',
Carl 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 ...
used a ranking scale limited to kingdom, class, order, genus, species, and one rank below species. Today, the nomenclature is regulated by the
nomenclature codes
Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species ...
. There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, and species. In addition, ''domain'' (proposed by
Carl Woese
Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist and biophysicist. Woese is famous for defining the Archaea (a new domain of life) in 1977 through a pioneering phylogenetic taxonomy of 16S ribosomal RNA, ...
) 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.
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
Binomial may refer to:
In mathematics
*Binomial (polynomial), a polynomial with two terms
* Binomial coefficient, numbers appearing in the expansions of powers of binomials
*Binomial QMF, a perfect-reconstruction orthogonal wavelet decomposition
...
, that is, a two-term name. For example, the zoological name for the human species is ''Homo sapiens''. This is usually italicized in print or 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.
Ranks in zoology
There are definitions of the following taxonomic ranks in the
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...
: 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:
----
:Superfamily
''
Family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
''
:
Subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
:
Tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English language, English is in the discipline of anthropology. This definition is contested, in p ...
:
Subtribe
----
''
Genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''
:
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 t ...
----
''
Species
In biology, a species is the basic unit of 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 individuals of the appropriate s ...
''
:
Subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
----
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
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 ...
with many species, e.g. the genus ''
Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
''. (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, ''infra''order (below suborder) or ''infra''family (below subfamily).
Names of zoological taxa
* A taxon above the rank of species has a scientific name in one part (a uninominal name).
* A species has a name composed of two parts (a binomial name or
binomen):
generic name +
specific name; for example ''Canis lupus''.
* A subspecies has a name composed of three parts (a trinomial name or
trinomen
In biology, trinomial nomenclature refers to names for taxa below the rank of species. These names have three parts. The usage is different in zoology and botany.
In zoology
In zoological nomenclature, a trinomen (), trinominal name, or ternary ...
): generic name + specific name +
subspecific name
In zoological nomenclature, a subspecific name is the third part of a trinomen. In zoology there is only one rank below that of species, namely "subspecies".
In botanical nomenclature, there are several levels of subspecific names, such as ''vari ...
; for example ''Canis lupus italicus''. As there is only one possible rank below that of species, no connecting term to indicate rank is needed or used.
Ranks in botany
According to Art 3.1 of the
(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:
----
''primary ranks''
:''secondary ranks''
::''further ranks''
----
''kingdom'' (''regnum'')
::''subregnum''
''division'' or phylum (''divisio'', ''phylum'')
::''subdivisio'' or ''subphylum''
''class'' (''classis'')
::''subclassis''
''order'' (''ordo'')
::''subordo''
----
''family'' (''familia'')
::''subfamilia''
:tribe (''tribus'')
::''subtribus''
''genus'' (''genus'')
::''subgenus''
:section (''sectio'')
::''subsection''
:series (''series'')
::''subseries''
''species'' (''species'')
::''subspecies''
:variety (''varietas'')
::''subvarietas''
:form (''forma'')
::''subforma''
----
There are definitions of the following taxonomic categories in the
International Code of Nomenclature for Cultivated Plants
The ''International Code of Nomenclature for Cultivated Plants'' (ICNCP), is a guide to the rules and regulations for naming cultigens, plants whose origin or selection is primarily due to intentional human activity. It is also known as Cultivate ...
:
cultivar group
A Group (previously cultivar-groupInternational Code of Nomenclature for Cultivated Plants, 4th edition (1969), 5th edition (1980) and 6th edition (1995)) is a formal category in the ''International Code of Nomenclature for Cultivated Plants'' ('' ...
,
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
,
grex
Grex or GREX may refer to:
* Grex (biology), a multicellular aggregate of amoeba of the phyla Acrasiomycota or Dictyosteliomycota
* Grex (horticulture), (pl. greges) a kind of group used in horticultural nomenclature applied to the progeny of an a ...
.
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 name Descriptive botanical names are scientific names of groups of plants that are irregular, not being derived systematically from the name of a type genus. They may describe some characteristics of the group in general or may be a name already in exi ...
.
Names of botanical taxa
Taxa at the rank of genus and above have a
botanical name
A botanical name is a formal scientific name conforming to the '' International Code of Nomenclature for algae, fungi, and plants'' (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the ''Intern ...
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
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 of living things by giving each a name composed of two parts, bot ...
); all taxa below the rank of species have a botanical name in three parts (an
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 ...
). 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
''Poa secunda'' (variously known by the common names of Sandberg bluegrass, alkali bluegrass, big bluegrass, Canby's bluegrass, Nevada bluegrass, one-sided bluegrass, Pacific bluegrass, pine blugrass, slender bluegrass, wild bluegrass, and curly ...
''.
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
In botanical nomenclature, a hybrid may be given a hybrid name, which is a special kind of botanical name, but there is no requirement that a hybrid name should be created for plants that are believed to be of hybrid origin. The '' International C ...
, the same ranks apply, prefixed with ''notho'' (Greek: 'bastard'), with nothogenus as the highest permitted rank.
Outdated names for botanical ranks
If a different term for the rank was used in an old publication, but the intention is clear, botanical nomenclature specifies certain substitutions:
* If names were "intended as names of orders, but published with their rank denoted by a term such as": "cohors"
see_also_cohort_study.html" ;"title="atin for "cohort"; see also cohort study">atin for "cohort"; see also cohort study for the use of the term in ecology], "nixus", "alliance", or "Reihe" instead of "order" (Article 17.2), they are treated as names of orders.
* "Family" is substituted for "order" (ordo) or "natural order" (ordo naturalis) under certain conditions where the modern meaning of "order" was not intended. (Article 18.2)
* "Subfamily is substituted for "suborder" (subordo) under certain conditions where the modern meaning of "suborder" was not intended. (Article 19.2)
* In a publication prior to 1 January 1890, if only one infraspecific rank is used, it is considered to be that of variety. (Article 37.4) This commonly applies to publications that labelled infraspecific taxa with Greek letters, α, β, γ, ...
Examples
Classifications of five species follow: the
fruit fly familiar in genetics laboratories (''Drosophila melanogaster''),
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
s (''Homo sapiens''), the
pea
The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
s used by
Gregor Mendel
Gregor Johann Mendel, Augustinians, OSA (; cs, Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) was a biologist, meteorologist, mathematician, Augustinians, Augustinian friar and abbot of St Thomas's Abbey, Brno, St. Thomas' Abbey in Brà ...
in his discovery of
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
(''Pisum sativum''), the "fly agaric" mushroom ''
Amanita muscaria
''Amanita muscaria'', commonly known as the fly agaric or fly amanita, is a basidiomycete of the genus ''Amanita''. It is also a muscimol mushroom. Native throughout the temperate and boreal regions of the Northern Hemisphere, ''Amanita muscar ...
'', and the bacterium ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
''. The eight major ranks are given in bold; a selection of minor ranks are given as well.
;Table notes
*In order to keep the table compact and avoid disputed technicalities, some common and uncommon intermediate ranks are omitted. For example, the
mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
of Europe, Africa, and upper North America are in class
Mammalia
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
, legion
Cladotheria
Cladotheria is a clade (sometimes ranked as a legion) of mammals. It contains modern therian mammals (marsupials and placentals) and several extinct groups, such as the dryolestoids, amphitheriids and peramurids. The clade was named in 1975 by M ...
, sublegion
Zatheria
Cladotheria is a clade (sometimes ranked as a legion) of mammals. It contains modern therian mammals (marsupials and placentals) and several extinct groups, such as the dryolestoids, amphitheriids and peramurids. The clade was named in 1975 by M ...
, infralegion
Tribosphenida
Tribosphenida is a group (infralegion) of mammals that includes the ancestor of ''Hypomylos'', Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants). Its current definition is more or less sy ...
, subclass
Theria
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes.
Ch ...
, clade
Eutheria
Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials.
Eutherians are distinguished from noneutherians by various phenotypic tra ...
, clade
Placentalia
Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...
– but only Mammalia and Theria are in the table. Legitimate arguments might arise if the commonly used clades Eutheria and Placentalia were both included, over which is the rank "infraclass" and what the other's rank should be, or whether the two names are synonyms.
*The ranks of higher taxa, especially intermediate ranks, are prone to revision as new information about relationships is discovered. For example, the
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s have been downgraded from a division (Magnoliophyta) to a subclass (Magnoliidae), and the superorder has become the rank that distinguishes the major groups of flowering plants. The traditional classification of primates (class Mammalia, subclass Theria, infraclass Eutheria, order Primates) has been modified by new classifications such as McKenna and Bell (class Mammalia, subclass Theriformes, infraclass Holotheria) with Theria and Eutheria assigned lower ranks between infraclass and the order Primates. See
mammal classification
Mammalia is a class of animal within the phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilso ...
for a discussion. These differences arise because there are few available ranks and many branching points in the fossil record.
*Within species further units may be recognised. Animals may be classified into subspecies (for example, ''Homo sapiens sapiens'', modern humans) or
morph
Morph may refer to:
Biology
* Morph (zoology), a visual or behavioral difference between organisms of distinct populations in a species
* Muller's morphs, a classification scheme for genetic mutations
* "-morph", a suffix commonly used in tax ...
s (for example ''Corvus corax varius'' morpha ''leucophaeus'', the pied raven). Plants may be classified into subspecies (for example, ''Pisum sativum'' subsp. ''sativum'', the garden pea) or varieties (for example, ''Pisum sativum'' var. ''macrocarpon'', snow pea), with cultivated plants getting a
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
name (for example, ''Pisum sativum'' var. ''macrocarpon'' 'Snowbird'). Bacteria may be classified by
strains (for example
''Escherichia coli'' O157:H7, a strain that can cause
food poisoning).
Terminations of names
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 ...
above the genus level are often given names based on 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 f ...
, 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 rather than for stressed ''a''.
;Table notes:
* In botany and mycology names at the rank of family and below are based on the name of a genus, sometimes called 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 f ...
of that taxon, with a standard ending. For example, the rose family,
Rosaceae
Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera.
The name is derived from the type genus ''Rosa''. Among the most species-rich genera are ''Alchemilla'' (270), ''Sorbus ...
, is named after the genus ''Rosa'', with the standard ending "-aceae" for a family. Names above the rank of family are also formed from a generic name, or are descriptive (like
Gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, Î³Ï…Î¼Î½ÏŒÏ ...
ae or
Fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
).
* For animals, there are standard suffixes for taxa only up to the rank of superfamily. Uniform suffix has been suggested (but not recommended) in
AAAS as ''-ida'' for orders, for example; protozoologists seem to adopt this system. Many metazoan (higher animals) orders also have such suffix, e.g.
Hyolithida
The Hyolithida are lophophorate
The Lophophorata are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phylogenetic analyses suggest that lophophorates are protostomes
Protostomia () i ...
and
Nectaspida (Naraoiida).
* Forming a name based on a generic name may be not straightforward. For example, the has the genitive , thus the genus ''Homo'' (human) is in the
Hominidae
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ea ...
, not "Homidae".
* The ranks of epifamily, infrafamily and infratribe (in animals) are used where the complexities of phyletic branching require finer-than-usual distinctions. Although they fall below the rank of superfamily, they are not regulated under the International Code of Zoological Nomenclature and hence do not have formal standard endings. The suffixes listed here are regular, but informal.
* In virology, the formal endings for taxa of
viroid
Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms (flowering plants), and most cause diseases, whose respective economi ...
s and of
satellite nucleic acids are similar to viruses, only -vir- is replaced by -viroid-, -satellit-.
[
]
All ranks
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
Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species ...
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:
* Domain
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
* Do ...
or Empire
** Subdomain (biology)
In biological taxonomy, a domain ( or ) (Latin: ''regio''), also dominion, superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together. It was introduced in the three-domain system of taxonomy devised by Carl W ...
* Realm
A realm is a community or territory over which a sovereign rules. The term is commonly used to describe a monarchical or dynastic state. A realm may also be a subdivision within an empire, if it has its own monarch, e.g. the German Empire.
Etym ...
(in virology)
** Subrealm (in virology)
* Hyperkingdom
In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.
Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (Animalia, Plant ...
** Superkingdom
In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.
Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (Animalia, Plant ...
*** 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 ...
**** Subkingdom
In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.
Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (Animalia, Plant ...
***** Infrakingdom
****** Parvkingdom
* Superphylum, or superdivision (in botany)
** Phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
, or division
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
*Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
(in botany)
*** Subphylum
In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum.
The taxonomic rank of "subdivision (rank), subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy. Some plant taxonomists ...
, or subdivision (in botany)
**** Infraphylum
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. Some plant taxonomists have also used the ...
, or infradivision (in botany)
***** Microphylum
* Superclass
** Class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
*** Subclass
**** Infraclass
In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdo ...
***** Subterclass
In Taxonomy (biology), biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are l ...
****** Parvclass
In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdo ...
* Superdivision (in zoology)
** Division
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
*Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
(in zoology)[These are movable ranks, most often inserted between the class and the legion or cohort. Nevertheless, their positioning in the zoological hierarchy may be subject to wide variation. For examples, see th]
Benton classification of vertebrates
(2005).
*** Subdivision (in zoology)
**** Infradivision (in zoology)
* Superlegion (in zoology)
** Legion
Legion may refer to:
Military
* Roman legion, the basic military unit of the ancient Roman army
* Spanish Legion, an elite military unit within the Spanish Army
* Legion of the United States, a reorganization of the United States Army from 179 ...
(in zoology)
*** Sublegion (in zoology)
**** Infralegion (in zoology)
* Supercohort (in zoology)[In zoological classification, the cohort and its associated group of ranks are inserted between the class group and the ordinal group. The cohort has also been used between infraorder and family in ]saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n dinosaurs
Benton
2005). In botanical classification, the cohort group has sometimes been inserted between the division (phylum) group and the class group: see Willis & McElwain (2002: 100–101), or has sometimes been used at the rank of order, and is now considered to be an obsolete name for order: See International Code of Nomenclature for algae, fungi, and plants, Melbourne Code 2012, Article 17.2.
** Cohort (in zoology)
*** Subcohort (in zoology)
**** Infracohort (in zoology)
* Gigaorder (in zoology)
** Magnorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
or megaorder (in zoology)[The supra-ordinal sequence gigaorder–megaorder–capaxorder–hyperorder (and the microorder, in roughly the position most often assigned to the parvorder) has been employed in turtles at least (Gaffney & Meylan 1988), while the parallel sequence magnorder–grandorder–mirorder figures in recently influential classifications of mammals. It is unclear from the sources how these two sequences are to be coordinated (or interwoven) within a unitary zoological hierarchy of ranks. Previously, Novacek (1986) and McKenna-Bell (1997) had inserted mirorders and grandorders between the order and superorder, but Benton (2005) now positions both of these ranks above the superorder.]
*** Grandorder or capaxorder (in zoology)
**** Mirorder or hyperorder (in zoology)
***** Superorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
****** Series (for fish)
******* Order
******** Parvorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
(position in some zoological classifications)
********* Nanorder (in zoology)
********** Hypoorder (in zoology)
*********** Minorder (in zoology)
************ Suborder
************* Infraorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
************** Parvorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
(usual position), or microorder (in zoology)
* Section (in zoology)
** Subsection (in zoology)
* Gigafamily (in zoology)
** Megafamily (in zoology)
*** Grandfamily (in zoology)
**** Hyperfamily (in zoology)
***** Superfamily
****** Epifamily (in zoology)
******* Series (for Lepidoptera)
******** Group (for Lepidoptera)
********* Family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
********** Subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
*********** Infrafamily
* Supertribe
** Tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English language, English is in the discipline of anthropology. This definition is contested, in p ...
*** Subtribe
**** Infratribe
* Supergenus
** Genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
*** 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 t ...
**** Section
Section, Sectioning or Sectioned may refer to:
Arts, entertainment and media
* Section (music), a complete, but not independent, musical idea
* Section (typography), a subdivision, especially of a chapter, in books and documents
** Section sign ...
(in botany)
***** Subsection (in botany)
****** Series
Series may refer to:
People with the name
* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
Arts, entertainment, and media
Music
* Series, the ordered sets used in ...
(in botany)
******* Subseries (in botany)
* Species complex
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
** Species
In biology, a species is the basic unit of 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 individuals of the appropriate s ...
*** Subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
, or ''forma specialis
''Forma specialis'' (plural: ''formae speciales''), abbreviated f. sp. (plural ff. spp.) without italics, is an informal taxonomic grouping allowed by the International Code of Nomenclature for algae, fungi, and plants, that is applied to a paras ...
'' (for fungi), or pathovar
A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one o ...
(for bacteria))
**** Variety
Variety may refer to:
Arts and entertainment Entertainment formats
* Variety (radio)
* Variety show, in theater and television
Films
* ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont
* ''Variety'' (1935 film), ...
or ''varietas'' (in botany); or form
Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens.
Form also refers to:
*Form (document), a document (printed or electronic) with spaces in which to write or enter data
...
or morph
Morph may refer to:
Biology
* Morph (zoology), a visual or behavioral difference between organisms of distinct populations in a species
* Muller's morphs, a classification scheme for genetic mutations
* "-morph", a suffix commonly used in tax ...
(in zoology) or aberration (in lepidopterology)
***** Subvariety (in botany)
****** Form
Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens.
Form also refers to:
*Form (document), a document (printed or electronic) with spaces in which to write or enter data
...
or ''forma'' (in botany)
Significance and problems
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 groups.
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
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
, that is, the phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
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 name In biological classification, circumscriptional names are taxon names that are not ruled by ICZN and are defined by the particular set of members included. Circumscriptional names are used mainly for taxa above family-group level (e. g. order or ...
s, avoid this problem. The theoretical difficulty with superimposing taxonomic ranks over evolutionary trees is manifested as the boundary paradox which may be illustrated by Darwinian evolutionary models.
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).[Stuessy, T.F. (2009). ''Plant Taxonomy: The Systematic Evaluation of Comparative Data.'' 2nd ed. Columbia University Press, p. 175.][Brusca, R.C. & Brusca, G.J. (2003). ''Invertebrates''. 2nd ed. Sunderland, Massachusetts: Sinauer Associates, pp. 26–27.] It should be a natural group (that is, non-artificial, non-polyphyletic
A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...
), 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
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
rank is usually associated with a certain body plan
A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.
This term, usually applied to animals, envisages a "blueprin ...
, which is also, however, an arbitrary criterion.
Mnemonic
There are several acronyms intended to help memorise the taxonomic hierarchy, such as "King Phillip came over for great spaghetti". See taxonomy mnemonic
Taxonomy mnemonics are used to memorize the scientific classification applied in taxonomy. They are usually constructed with a series of words that begin with the letters KPCOFGS, corresponding to the initials of the primary taxonomic ranks. Words ...
. In Season 3, episode 16 ("Virtual Systems Analysis" ) of the NBC comedy Community
A community is a social unit (a group of living things) with commonality such as place, norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area (e.g. a country, village, tow ...
the character Hawthorne Pierce (Chevy Chase) refers to the mnemonic variant "Kevin, Please Come Over for Gay Sex."
See also
* Breed
A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slig ...
* Catalogue of Life
The Catalogue of Life is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxonomic Info ...
(a database)
* Cladistics
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
* Landrace
A landrace is a domesticated, locally adapted, often traditional variety of a species of animal or plant that has developed over time, through adaptation to its natural and cultural environment of agriculture and pastoralism, and due to isolation ...
* Tree of life (biology)
The tree of life or universal tree of life is a metaphor, model and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Dar ...
Footnotes
References
Bibliography
*
* Benton, Michael J. 2005. ''Vertebrate Palaeontology'', 3rd ed. Oxford: Blackwell Publishing. .
* Brummitt, R.K., and C.E. Powell. 1992. '' Authors of Plant Names''. Royal Botanic Gardens, Kew.
* Carroll, Robert L. 1988. ''Vertebrate Paleontology and Evolution''. New York: W.H. Freeman & Co.
* Gaffney, Eugene S., and Peter A. Meylan. 1988. "A phylogeny of turtles". In M.J. Benton (ed.), ''The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds'', 157–219. Oxford: Clarendon Press.
* Haris Abba Kabara. 2001. ''Karmos hand book for botanical names''.
* Lambert, David. 1990. ''Dinosaur Data Book''. Oxford: Facts on File & British Museum (Natural History).
* McKenna, Malcolm C., and Susan K. Bell (editors). 1997. ''Classification of Mammals Above the Species Level''. New York: Columbia University Press.
* Milner, Andrew. 1988. "The relationships and origin of living amphibians". In M.J. Benton (ed.), ''The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds'', 59–102. Oxford: Clarendon Press.
* Novacek, Michael J. 1986. "The skull of leptictid insectivorans and the higher-level classification of eutherian mammals". ''Bulletin of the American Museum of Natural History'' 183: 1–112.
* Sereno, Paul C. 1986. "Phylogeny of the bird-hipped dinosaurs (Order Ornithischia)". ''National Geographic Research'' 2: 234–56.
* Willis, K.J., and J.C. McElwain. 2002. ''The Evolution of Plants''. Oxford University Press.
{{Taxonomic ranks
Botanical nomenclature
Plant taxonomy
R
Biology terminology