Taxonomic rank

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The major ranks: domain, kingdom, phylum, class, order, family, genus, and species, applied to the red fox, Vulpes vulpes. Taxonomic Rank Graph.svg
The major ranks: domain, kingdom, phylum, class, order, family, genus, and species, applied to the red fox, Vulpes vulpes.
The hierarchy of biological classification's eight major taxonomic ranks. Intermediate minor rankings are not shown. Biological classification L Pengo vflip.svg DomainKingdomClassOrderFamily
The hierarchy of biological classification's eight major taxonomic ranks. Intermediate minor rankings are not shown.

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. [1]

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)." [2]

Main ranks

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. [3] [4]

Main taxonomic ranks
regio domain
regnum kingdom
phylum phylum (in zoology) / division (in botany)
classis class
ordo order
familia family
genus genus
species species

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, 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: 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.[ citation needed ])

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).

Names of zoological taxa

Ranks in botany

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: [5]

primary ranks

secondary ranks
further ranks

kingdom (regnum)


division or phylum (divisio, phylum)

subdivisio or subphylum

class (classis)


order (ordo)


family (familia)

tribe (tribus)

genus (genus)

section (sectio)
series (series)

species (species)

variety (varietas)
form (forma)

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 name.

Names of botanical taxa

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 . [6]

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. [7]

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:[ citation needed ]

  • If names were "intended as names of orders, but published with their rank denoted by a term such as": "cohors" [Latin for "cohort"; [8] 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, ...


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
Domain Eukarya Eukarya Eukarya Eukarya Bacteria
Kingdom Animalia Animalia Plantae Fungi
Phylum or division Arthropoda Chordata Magnoliophyta (Tracheophyta) Basidiomycota Proteobacteria
Subphylum or subdivision Hexapoda Vertebrata Magnoliophytina (Euphyllophytina) Agaricomycotina
Class Insecta Mammalia Magnoliopsida (Equisetopsida) Agaricomycetes Gammaproteobacteria
Subclass Pterygota Theria Rosidae (Magnoliidae) Agaricomycetidae
Superorder Panorpida Euarchontoglires Rosanae
Order Diptera Primates Fabales Agaricales Enterobacterales
Suborder Brachycera Haplorrhini FabineaeAgaricineae
Family Drosophilidae Hominidae Fabaceae Amanitaceae Enterobacteriaceae
Subfamily Drosophilinae Homininae Faboideae Amanitoideae
Tribe Hominini Fabeae
Genus Drosophila Homo Pisum Amanita Escherichia
Species D. melanogaster H. sapiens P. sativum A. muscaria E. coli
Table notes

Terminations of names

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 // for stressed a.

Rank Bacteria [10] Plants Algae Fungi Animals Viruses [11]
Division/phylum-ophyta [12] /ˈɒfətə,ə(ˈ)ftə/ -mycota /mˈktə/ -viricota /vɪrəˈktə/
Subdivision/subphylum-phytina [12] /fəˈtnə/ -mycotina /mkəˈtnə/ -viricotina /vɪrəkəˈtnə/
Class-ia /iə/ -opsida /ˈɒpsədə/ -phyceae /ˈfʃ/ -mycetes /mˈstz/ -viricetes /vɪrəˈstz/
Subclass-idae /əd/ -phycidae /ˈfɪsəd/ -mycetidae /mˈsɛtəd/ -viricetidae /vɪrəˈsɛtəd/
Superorder-anae /ˈn/
Order-ales /ˈlz/ -ida /ədə/ or -iformes /ə(ˈ)fɔːrmz/ -virales /vˈrlz/
Suborder-ineae /ˈɪn/ -virineae /vəˈrɪn/
Infraorder-aria /ˈɛəriə/
Superfamily-acea /ˈʃə/ -oidea /ˈɔɪdə/
Epifamily-oidae /ˈɔɪd/
Family-aceae /ˈʃ/ -idae /əd/ -viridae /ˈvɪrəd/
Subfamily-oideae /ˈɔɪd/ -inae /ˈn/ -virineae /vɪˈrɪn/
Infrafamily-odd /ɒd/ [13]
Tribe-eae // -ini /ˈn/
Subtribe-inae /ˈn/ -ina /ˈnə/
Infratribe-ad /æd/ or -iti /ˈti/
Table notes

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 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: [17]

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. [22] 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.[ citation needed ]

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.[ citation needed ]

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. [23] [24] 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). [25] [26] 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). [26] For animals, at least the phylum rank is usually associated with a certain body plan, which is also, however, an arbitrary criterion.[ citation needed ]


There are several acronyms intended to help memorise the taxonomic hierarchy, such as "King Phillip came over for great spaghetti". See taxonomy mnemonic.

See also


  1. The Virginia opossum is an exception.

Related Research Articles

Linnaean taxonomy Rank based classification system for organisms

Linnaean taxonomy can mean either of two related concepts:

  1. the particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his Systema Naturae (1735) and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and they, in turn, into lower ranks in a hierarchical order.
  2. a term for rank-based classification of organisms, in general. That is, taxonomy in the traditional sense of the word: rank-based scientific classification. This term is especially used as opposed to cladistic systematics, which groups organisms into clades. It is attributed to Linnaeus, although he neither invented the concept of ranked classification nor gave it its present form. In fact, it does not have an exact present form, as "Linnaean taxonomy" as such does not really exist: it is a collective (abstracting) term for what actually are several separate fields, which use similar approaches.
Taxonomy (biology) Science of naming, defining and classifying organisms

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 and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum, class, order, family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, as he developed a ranked system known as Linnaean taxonomy for categorizing organisms and binominal nomenclature for naming organisms.

Genus Taxonomic rank used in the biological classification of living and fossil organisms, and viruses

Genus /ˈdʒiː.nəs/ is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. 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.

In biological classification, the order is

  1. a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: life, domain, kingdom, phylum, class, order, family, genus, and species, with order fitting in between class and family. An immediately higher rank, superorder, is sometimes added directly above order, with suborder directly beneath order.
  2. a taxonomic unit in the rank of order. In that case the plural is orders.
Subspecies Taxonomic rank subordinate to species

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 may be abbreviated to subsp. or ssp. The plural is the same as the singular: subspecies.

Taxon Group of one or more populations of an organism or organisms which have distinguishing characteristics in common

In biology, a taxon 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 name and given a particular ranking, especially if and when it is accepted or becomes established. It is very common, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion. If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

In botanical nomenclature, variety 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.

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.

Type species Term used in biological nomenclature

In zoological nomenclature, a type species is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen(s). A similar concept is used for suprageneric groups and called a type genus.

Form (botany) One of the secondary taxonomic ranks, below that of variety, in botanical nomenclature

In botanical nomenclature, a form is one of the "secondary" taxonomic ranks, below that of variety, which in turn is below that of species; it is an infraspecific taxon. If more than three ranks are listed in describing a taxon, the "classification" is being specified, but only three parts make up the "name" of the taxon: a genus name, a specific epithet, and an infraspecific epithet.

<i>Incertae sedis</i> Term to indicate an uncertain taxonomic position

Incertae sedis or problematica is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae, incerti subordinis, incerti ordinis and similar terms.

Botanical name Scientific name for a plant, alga or fungus

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 International Code of Nomenclature for Cultivated Plants (ICNCP). The code of nomenclature covers "all organisms traditionally treated as algae, fungi, or plants, whether fossil or non-fossil, including blue-green algae (Cyanobacteria), chytrids, oomycetes, slime moulds and photosynthetic protists with their taxonomically related non-photosynthetic groups ."

Botanical nomenclature is the formal, scientific naming of plants. It is related to, but distinct from taxonomy. Plant taxonomy is concerned with grouping and classifying plants; botanical nomenclature then provides names for the results of this process. The starting point for modern botanical nomenclature is Linnaeus' Species Plantarum of 1753. Botanical nomenclature is governed by the International Code of Nomenclature for algae, fungi, and plants (ICN), which replaces the International Code of Botanical Nomenclature (ICBN). Fossil plants are also covered by the code of nomenclature.

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 are assignable to families, it may not be noticeable that there is more than one code, but beyond this basic level these are rather different in the way they work.

In botany, an infraspecific name is the scientific name for any taxon below the rank of species, i.e. an infraspecific taxon or infraspecies. The scientific names of botanical taxa are regulated by the International Code of Nomenclature for algae, fungi, and plants (ICN). This specifies a 'three part name' for infraspecific taxa, plus a 'connecting term' to indicate the rank of the name. An example of such a name is Astrophytum myriostigma subvar. glabrum, the name of a subvariety of the species Astrophytum myriostigma.

In botanical nomenclature, author citation is the way of citing the person or group of people who validly published a botanical name, i.e. who first published the name while fulfilling the formal requirements as specified by the International Code of Nomenclature for algae, fungi, and plants (ICN). In cases where a species is no longer in its original generic placement, both the authority for the original genus placement and that for the new combination are given.

In botanical nomenclature, autonyms are automatically created names, as regulated by the International Code of Nomenclature for algae, fungi, and plants that are created for certain subdivisions of genera and species, those that include the type of the genus or species. An autonym might not be mentioned in the publication that creates it as a side-effect. Autonyms "repeat unaltered" the genus name or species epithet of the taxon being subdivided, and no other name for that same subdivision is validly published. For example, Rubus subgenus Eubatus is not validly published, and the subgenus is known as Rubus subgen. Rubus.

The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies. This name is no longer in use, so it is now a synonym of the current scientific name, Picea abies. In zoology, moving a species from one genus to another results in a different binomen, but the name is considered an alternative combination, rather than a synonym. The concept of synonymy in zoology is reserved for two names at the same rank that refer to a taxon at that rank - for example, the name Papilio prorsaLinnaeus, 1758 is a junior synonym of Papilio levanaLinnaeus, 1758, being names for different seasonal forms of the species now referred to as Araschnia levana(Linnaeus, 1758), the map butterfly. However, Araschnia levana is not a synonym of Papilio levana in the taxonomic sense employed by the Zoological code.

In zoology, the principle of coordination is one of the guiding principles of the International Code of Zoological Nomenclature.

This is a list of terms and symbols used in scientific names for organisms, and in describing the names. For proper parts of the names themselves, see List of Latin and Greek words commonly used in systematic names. Note that many of the abbreviations are used with or without a stop.


  1. "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". 2012. Articles 2 and 3.
  2. International Commission on Zoological Nomenclature (1999), International Code of Zoological Nomenclature. Fourth Edition, International Trust for Zoological Nomenclature
  3. Moore, R. T. (1974). "Proposal for the recognition of super ranks" (PDF). Taxon. 23 (4): 650–652. doi:10.2307/1218807. JSTOR   1218807.
  4. Luketa, S. (2012). "New views on the megaclassification of life" (PDF). Protistology. 7 (4): 218–237.
  5. "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". 2012. Articles 3 and 4.
  6. "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". 2012. Articles 4.2 and 24.1.
  7. "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". 2012. Article 3.2, and Appendix 1, Articles H.1–3.
  8. Stearn, W.T. 1992. Botanical Latin: History, grammar, syntax, terminology and vocabulary, Fourth edition. David and Charles.
  9. Chase, M.W.; Reveal, J.L. (2009), "A phylogenetic classification of the land plants to accompany APG III", Botanical Journal of the Linnean Society, 161 (2): 122–127, doi: 10.1111/j.1095-8339.2009.01002.x
  10. Euzéby, J. P. (1997). "List of Bacterial Names with Standing in Nomenclature: a folder available on the Internet (13 Dec. 2007 version)". International Journal of Systematic and Evolutionary Microbiology . 47 (2): 590–592. doi: 10.1099/00207713-47-2-590 . PMID   9103655.
  11. 1 2 3 4 "ICTV Code. Section 3.IV, § 3.23; section 3.V, §§ 3.27-3.28." International Committee on Taxonomy of Viruses. October 2018. Retrieved 28 November 2018.
  12. 1 2 "International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code)". 2018. Article 16.
  13. For example, the chelonian infrafamilies Chelodd (Gaffney & Meylan 1988: 169) and Baenodd (ibid., 176).
  14. ICZN article 29.2
  15. Pearse, A.S. (1936) Zoological names. A list of phyla, classes, and orders, prepared for section F, American Association for the Advancement of Science. American Association for the Advancement of Science, p. 4
  16. As supplied by Gaffney & Meylan (1988).
  17. For the general usage and coordination of zoological ranks between the phylum and family levels, including many intercalary ranks, see Carroll (1988). For additional intercalary ranks in zoology, see especially Gaffney & Meylan (1988); McKenna & Bell (1997); Milner (1988); Novacek (1986, cit. in Carroll 1988: 499, 629); and Paul Sereno's 1986 classification of ornithischian dinosaurs as reported in Lambert (1990: 149, 159). For botanical ranks, including many intercalary ranks, see Willis & McElwain (2002).
  18. 1 2 3 4 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 the Benton classification of vertebrates (2005).
  19. 1 2 3 4 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 saurischian 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.
  20. 1 2 3 4 5 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.
  21. Additionally, the terms biovar, morphovar, phagovar, and serovar designate bacterial strains (genetic variants) that are physiologically or biochemically distinctive. These are not taxonomic ranks, but are groupings of various sorts which may define a bacterial subspecies.
  22. Gingerich, P. D. (1987). "Evolution and the fossil record: patterns, rates, and processes". Canadian Journal of Zoology. 65 (5): 1053–1060. doi:10.1139/z87-169.
  23. Kluge, N.J. (1999). "A system of alternative nomenclatures of supra-species taxa. Linnaean and post-Linnaean principles of systematics". Entomological Review. 79 (2): 133–147.
  24. Kluge, N.J. (2010). "Circumscriptional names of higher taxa in Hexapoda". Bionomina. 1 (1): 15–55. doi: 10.11646/bionomina.1.1.3 .
  25. Stuessy, T.F. (2009). Plant Taxonomy: The Systematic Evaluation of Comparative Data. 2nd ed. Columbia University Press, p. 175.
  26. 1 2 Brusca, R.C. & Brusca, G.J. (2003). Invertebrates. 2nd ed. Sunderland, Massachusetts: Sinauer Associates, pp. 26–27.


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