Taxonomic rank

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In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in a taxonomic hierarchy. Taxonomic rank_sentence_0

Examples of taxonomic ranks are species, genus, family, order, class, phylum, kingdom, domain, etc. Taxonomic rank_sentence_1

A given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Taxonomic rank_sentence_2

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. Taxonomic rank_sentence_3

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. Taxonomic rank_sentence_4

Consider a particular species, the red fox, Vulpes vulpes: the next rank above, the genus Vulpes, comprises all the "true" foxes. Taxonomic rank_sentence_5

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). Taxonomic rank_sentence_6

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. Taxonomic rank_sentence_7

Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya. Taxonomic rank_sentence_8

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)." Taxonomic rank_sentence_9

Main ranks Taxonomic rank_section_0

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. Taxonomic rank_sentence_10

Today, nomenclature is regulated by the nomenclature codes. Taxonomic rank_sentence_11

There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, species. Taxonomic rank_sentence_12

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. Taxonomic rank_sentence_13

Taxonomic rank_table_general_0

Main taxonomic ranksTaxonomic rank_cell_0_0_0
LatinTaxonomic rank_cell_0_1_0 EnglishTaxonomic rank_cell_0_1_1
regioTaxonomic rank_cell_0_2_0 domainTaxonomic rank_cell_0_2_1
regnumTaxonomic rank_cell_0_3_0 kingdomTaxonomic rank_cell_0_3_1
phylumTaxonomic rank_cell_0_4_0 phylum / divisionTaxonomic rank_cell_0_4_1
classisTaxonomic rank_cell_0_5_0 classTaxonomic rank_cell_0_5_1
ordoTaxonomic rank_cell_0_6_0 orderTaxonomic rank_cell_0_6_1
familiaTaxonomic rank_cell_0_7_0 familyTaxonomic rank_cell_0_7_1
genusTaxonomic rank_cell_0_8_0 genusTaxonomic rank_cell_0_8_1
speciesTaxonomic rank_cell_0_9_0 speciesTaxonomic rank_cell_0_9_1

A taxon is usually assigned a rank when it is given its formal name. Taxonomic rank_sentence_14

The basic ranks are species and genus. Taxonomic rank_sentence_15

When an organism is given a species name it is assigned to a genus, and the genus name is part of the species name. Taxonomic rank_sentence_16

The species name is also called a binomial, that is, a two-term name. Taxonomic rank_sentence_17

For example, the zoological name for the human species is Homo sapiens. Taxonomic rank_sentence_18

This is usually italicized in print, or underlined when italics are not available. Taxonomic rank_sentence_19

In this case, Homo is the generic name and it is capitalized; sapiens indicates the species and it is not capitalized. Taxonomic rank_sentence_20

Ranks in zoology Taxonomic rank_section_1

There are definitions of the following taxonomic ranks in the International Code of Zoological Nomenclature: superfamily, family, subfamily, tribe, subtribe, genus, subgenus, species, subspecies. Taxonomic rank_sentence_21

The International Code of Zoological Nomenclature divides names into "family-group names", "genus-group names" and "species-group names". Taxonomic rank_sentence_22

The Code explicitly mentions the following ranks for these categories: Taxonomic rank_sentence_23

Taxonomic rank_description_list_0

  • SuperfamilyTaxonomic rank_item_0_0

Family Taxonomic rank_sentence_24

Taxonomic rank_description_list_1

Genus Taxonomic rank_sentence_25

Taxonomic rank_description_list_2

Species Taxonomic rank_sentence_26

Taxonomic rank_description_list_3

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. Taxonomic rank_sentence_27

Among "genus-group names" and "species-group names" no further ranks are officially allowed. Taxonomic rank_sentence_28

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. Taxonomic rank_sentence_29

(Note the potentially confusing use of "species group" as both a category of ranks as well as an unofficial rank itself.) Taxonomic rank_sentence_30

At higher ranks (family and above) a lower level may be denoted by adding the prefix "infra", meaning lower, to the rank. Taxonomic rank_sentence_31

For example, infraorder (below suborder) or infrafamily (below subfamily). Taxonomic rank_sentence_32

Names of zoological taxa Taxonomic rank_section_2

Taxonomic rank_unordered_list_4

  • A taxon above the rank of species has a scientific name in one part (a uninominal name).Taxonomic rank_item_4_6
  • A species has a name composed of two parts (a binomial name or binomen): generic name + specific name; for example Canis lupus.Taxonomic rank_item_4_7
  • A subspecies has a name composed of three parts (a trinomial name or trinomen): generic name + specific name + subspecific name; for example Canis lupus familiaris. As there is only one possible rank below that of species, no connecting term to indicate rank is needed or used.Taxonomic rank_item_4_8

Ranks in botany Taxonomic rank_section_3

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. Taxonomic rank_sentence_33

According to Art 4.1 the secondary ranks of taxa are tribe, section, series, variety and form. Taxonomic rank_sentence_34

There is an indeterminate number of ranks. Taxonomic rank_sentence_35

The ICN explicitly mentions: Taxonomic rank_sentence_36

primary ranks Taxonomic rank_sentence_37

Taxonomic rank_description_list_5

  • secondary ranksTaxonomic rank_item_5_9
    • further ranksTaxonomic rank_item_5_10

kingdom (regnum) Taxonomic rank_sentence_38

Taxonomic rank_description_list_6

  • Taxonomic rank_item_6_11
    • subregnumTaxonomic rank_item_6_12

division or phylum (divisio, phylum) Taxonomic rank_sentence_39

Taxonomic rank_description_list_7

  • Taxonomic rank_item_7_13
    • subdivisio or subphylumTaxonomic rank_item_7_14

class (classis) Taxonomic rank_sentence_40

Taxonomic rank_description_list_8

  • Taxonomic rank_item_8_15
    • subclassisTaxonomic rank_item_8_16

order (ordo) Taxonomic rank_sentence_41

Taxonomic rank_description_list_9

  • Taxonomic rank_item_9_17
    • subordoTaxonomic rank_item_9_18

family (familia) Taxonomic rank_sentence_42

Taxonomic rank_description_list_10

  • Taxonomic rank_item_10_19
    • subfamiliaTaxonomic rank_item_10_20
  • tribe (tribus)Taxonomic rank_item_10_21
    • subtribusTaxonomic rank_item_10_22

genus (genus) Taxonomic rank_sentence_43

Taxonomic rank_description_list_11

  • Taxonomic rank_item_11_23
    • subgenusTaxonomic rank_item_11_24
  • section (sectio)Taxonomic rank_item_11_25
    • subsectionTaxonomic rank_item_11_26
  • series (series)Taxonomic rank_item_11_27
    • subseriesTaxonomic rank_item_11_28

species (species) Taxonomic rank_sentence_44

Taxonomic rank_description_list_12

  • Taxonomic rank_item_12_29
    • subspeciesTaxonomic rank_item_12_30
  • variety (varietas)Taxonomic rank_item_12_31
    • subvarietasTaxonomic rank_item_12_32
  • form (forma)Taxonomic rank_item_12_33
    • subformaTaxonomic rank_item_12_34

There are definitions of the following taxonomic categories in the International Code of Nomenclature for Cultivated Plants: cultivar group, cultivar, grex. Taxonomic rank_sentence_45

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. Taxonomic rank_sentence_46

Also see descriptive botanical names. Taxonomic rank_sentence_47

Names of botanical taxa Taxonomic rank_section_4

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). Taxonomic rank_sentence_48

To indicate the rank of the infraspecific name, a "connecting term" is needed. Taxonomic rank_sentence_49

Thus Poa secunda subsp. Taxonomic rank_sentence_50

juncifolia, where "subsp." Taxonomic rank_sentence_51

is an abbreviation for "subspecies", is the name of a subspecies of Poa secunda. Taxonomic rank_sentence_52

Hybrids can be specified either by a "hybrid formula" that specifies the parentage, or may be given a name. Taxonomic rank_sentence_53

For hybrids receiving a hybrid name, the same ranks apply, prefixed with notho (Greek: 'bastard'), with nothogenus as the highest permitted rank. Taxonomic rank_sentence_54

Outdated names for botanical ranks Taxonomic rank_section_5

If a different term for the rank was used in an old publication, but the intention is clear, botanical nomenclature specifies certain substitutions: Taxonomic rank_sentence_55

Taxonomic rank_unordered_list_13

  • If names were "intended as names of orders, but published with their rank denoted by a term such as": "cohors" [Latin 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.Taxonomic rank_item_13_35
  • "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)Taxonomic rank_item_13_36
  • "Subfamily is substituted for "suborder" (subordo) under certain conditions where the modern meaning of "suborder" was not intended. (Article 19.2)Taxonomic rank_item_13_37
  • 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, ...Taxonomic rank_item_13_38

Biology such as a Ernest hackle(1894), Robert whittaker(1969) and carl woese(1977) have tried to classify all living organisms into to broad categories, called kingdoms. Taxonomic rank_sentence_56

Examples Taxonomic rank_section_6

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. Taxonomic rank_sentence_57

The eight major ranks are given in bold; a selection of minor ranks are given as well. Taxonomic rank_sentence_58

Taxonomic rank_description_list_14

Taxonomic rank_unordered_list_15

  • In order to keep the table compact and avoid disputed technicalities, some common and uncommon intermediate ranks are omitted. For example, the mammals of Europe, Africa, and upper North America are in class Mammalia, legion Cladotheria, sublegion Zatheria, infralegion Tribosphenida, subclass Theria, clade Eutheria, clade Placentalia – 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.Taxonomic rank_item_15_39
  • The ranks of higher taxa, especially intermediate ranks, are prone to revision as new information about relationships is discovered. For example, the flowering plants 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 for a discussion. These differences arise because there are few available ranks and many branching points in the fossil record.Taxonomic rank_item_15_40
  • Within species further units may be recognised. Animals may be classified into subspecies (for example, Homo sapiens sapiens, modern humans) or morphs (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 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).Taxonomic rank_item_15_41

Terminations of names Taxonomic rank_section_7

Taxa above the genus level are often given names based on the type genus, with a standard termination. Taxonomic rank_sentence_59

The terminations used in forming these names depend on the kingdom (and sometimes the phylum and class) as set out in the table below. Taxonomic rank_sentence_60

Pronunciations given are the most Anglicized. Taxonomic rank_sentence_61

More Latinate pronunciations are also common, particularly /ɑː/ rather than /eɪ/ for stressed a. Taxonomic rank_sentence_62

Taxonomic rank_description_list_16

Taxonomic rank_unordered_list_17

  • 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 of that taxon, with a standard ending. For example, the rose family, Rosaceae, 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 Gymnospermae or Fungi).Taxonomic rank_item_17_42
  • For animals, there are standard suffixes for taxa only up to the rank of superfamily.Taxonomic rank_item_17_43
  • Forming a name based on a generic name may be not straightforward. For example, the homo has the genitive hominis, thus the genus Homo (human) is in the Hominidae, not "Homidae".Taxonomic rank_item_17_44
  • 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.Taxonomic rank_item_17_45
  • Many animal orders have the informal suffix -ida /ɪdə/, e.g. Hyolithida and Nectaspida (Naraoiida)Taxonomic rank_item_17_46
  • In virology, the formal endings for taxa of viroids and of satellite nucleic acids are similar to viruses, only -vir- is replaced by -viroid-, -satellit-.Taxonomic rank_item_17_47

All ranks Taxonomic rank_section_8

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. Taxonomic rank_sentence_63

In doing so, there are some restrictions, which will vary with the nomenclature code which applies. Taxonomic rank_sentence_64

The following is an artificial synthesis, solely for purposes of demonstration of relative rank (but see notes), from most general to most specific: Taxonomic rank_sentence_65

Taxonomic rank_unordered_list_18

  • Domain or EmpireTaxonomic rank_item_18_48
  • Realm (in virology)Taxonomic rank_item_18_50
    • Subrealm (in virology)Taxonomic rank_item_18_51
  • HyperkingdomTaxonomic rank_item_18_52
    • SuperkingdomTaxonomic rank_item_18_53
      • KingdomTaxonomic rank_item_18_54
        • SubkingdomTaxonomic rank_item_18_55
          • InfrakingdomTaxonomic rank_item_18_56
            • ParvkingdomTaxonomic rank_item_18_57
  • Superphylum, or superdivision (in botany)Taxonomic rank_item_18_58
    • Phylum, or division (in botany)Taxonomic rank_item_18_59
      • Subphylum, or subdivision (in botany)Taxonomic rank_item_18_60
  • SuperclassTaxonomic rank_item_18_63
  • Superdivision (in zoology)Taxonomic rank_item_18_68
    • Division (in zoology)Taxonomic rank_item_18_69
      • Subdivision (in zoology)Taxonomic rank_item_18_70
        • Infradivision (in zoology)Taxonomic rank_item_18_71
  • Superlegion (in zoology)Taxonomic rank_item_18_72
    • Legion (in zoology)Taxonomic rank_item_18_73
      • Sublegion (in zoology)Taxonomic rank_item_18_74
        • Infralegion (in zoology)Taxonomic rank_item_18_75
  • Supercohort (in zoology)Taxonomic rank_item_18_76
    • Cohort (in zoology)Taxonomic rank_item_18_77
      • Subcohort (in zoology)Taxonomic rank_item_18_78
        • Infracohort (in zoology)Taxonomic rank_item_18_79
  • Gigaorder (in zoology)Taxonomic rank_item_18_80
    • Magnorder or megaorder (in zoology)Taxonomic rank_item_18_81
      • Grandorder or capaxorder (in zoology)Taxonomic rank_item_18_82
        • Mirorder or hyperorder (in zoology)Taxonomic rank_item_18_83
          • SuperorderTaxonomic rank_item_18_84
            • Series (for fish)Taxonomic rank_item_18_85
              • OrderTaxonomic rank_item_18_86
                • Parvorder (position in some zoological classifications)Taxonomic rank_item_18_87
                  • Nanorder (in zoology)Taxonomic rank_item_18_88
                    • Hypoorder (in zoology)Taxonomic rank_item_18_89
                      • Minorder (in zoology)Taxonomic rank_item_18_90
                        • SuborderTaxonomic rank_item_18_91
                          • InfraorderTaxonomic rank_item_18_92
                            • Parvorder (usual position), or microorder (in zoology)Taxonomic rank_item_18_93
  • Section (in zoology)Taxonomic rank_item_18_94
    • Subsection (in zoology)Taxonomic rank_item_18_95
  • Gigafamily (in zoology)Taxonomic rank_item_18_96
    • Megafamily (in zoology)Taxonomic rank_item_18_97
      • Grandfamily (in zoology)Taxonomic rank_item_18_98
        • Hyperfamily (in zoology)Taxonomic rank_item_18_99
          • SuperfamilyTaxonomic rank_item_18_100
            • Epifamily (in zoology)Taxonomic rank_item_18_101
              • Series (for Lepidoptera)Taxonomic rank_item_18_102
                • Group (for Lepidoptera)Taxonomic rank_item_18_103
                  • FamilyTaxonomic rank_item_18_104
                    • SubfamilyTaxonomic rank_item_18_105
                      • InfrafamilyTaxonomic rank_item_18_106
  • SupertribeTaxonomic rank_item_18_107
    • TribeTaxonomic rank_item_18_108
      • SubtribeTaxonomic rank_item_18_109
        • InfratribeTaxonomic rank_item_18_110
  • SupergenusTaxonomic rank_item_18_111
    • GenusTaxonomic rank_item_18_112
      • SubgenusTaxonomic rank_item_18_113
        • Section (in botany)Taxonomic rank_item_18_114
          • Subsection (in botany)Taxonomic rank_item_18_115
            • Series (in botany)Taxonomic rank_item_18_116
              • Subseries (in botany)Taxonomic rank_item_18_117
  • Superspecies or Species-groupTaxonomic rank_item_18_118
    • SpeciesTaxonomic rank_item_18_119
      • Subspecies, or forma specialis (for fungi), or pathovar (for bacteria))Taxonomic rank_item_18_120
        • Variety or varietas (in botany); or form or morph (in zoology) or aberration (in lepidopterology)Taxonomic rank_item_18_121
          • Subvariety (in botany)Taxonomic rank_item_18_122
            • Form or forma (in botany)Taxonomic rank_item_18_123
              • Subform (in botany)Taxonomic rank_item_18_124

Significance and problems Taxonomic rank_section_9

Ranks are assigned based on subjective dissimilarity, and do not fully reflect the gradational nature of variation within nature. Taxonomic rank_sentence_66

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. Taxonomic rank_sentence_67

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. Taxonomic rank_sentence_68

Of these many ranks, the most basic is species. Taxonomic rank_sentence_69

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. Taxonomic rank_sentence_70

It varies from case to case. Taxonomic rank_sentence_71

Ideally, a taxon is intended to represent a clade, that is, the phylogeny of the organisms under discussion, but this is not a requirement. Taxonomic rank_sentence_72

A classification in which all taxa have formal ranks cannot adequately reflect knowledge about phylogeny. Taxonomic rank_sentence_73

Since taxon names are dependent on ranks in traditional Linnaean systems of classification, taxa without ranks cannot be given names. Taxonomic rank_sentence_74

Alternative approaches, such as using circumscriptional names, avoid this problem. Taxonomic rank_sentence_75

The theoretical difficulty with superimposing taxonomic ranks over evolutionary trees is manifested as the boundary paradox which may be illustrated by Darwinian evolutionary models. Taxonomic rank_sentence_76

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). Taxonomic rank_sentence_77

It should be a natural group (that is, non-artificial, non-polyphyletic), as judged by a biologist, using all the information available to them. Taxonomic rank_sentence_78

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). Taxonomic rank_sentence_79

For animals, at least the phylum rank is usually associated with a certain body plan, which is also, however, an arbitrary criterion. Taxonomic rank_sentence_80

Mnemonic Taxonomic rank_section_10

There are several acronyms intended to help memorise the taxonomic hierarchy, such as "King Phillip came over for great spaghetti". Taxonomic rank_sentence_81

See taxonomy mnemonic. Taxonomic rank_sentence_82

See also Taxonomic rank_section_11

Taxonomic rank_unordered_list_19

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: rank.