Taxonomic rank

Source: Wikipedia, the free encyclopedia.

The major ranks: domain, kingdom, phylum, class, order, family, genus, and species, applied to the red fox, Vulpes vulpes.

In

phylum, kingdom, and domain designate rank. This page emphasizes absolute ranks and the rank-based codes (the Zoological Code, the Botanical Code, the Code for Cultivated Plants, the Prokaryotic Code, and the Code for Viruses) require them. However, absolute ranks are not required in all nomenclatural systems for taxonomists; for instance, the PhyloCode,[2] the code of phylogenetic nomenclature
, does not require absolute ranks.

Taxa are hierarchical groups of organisms, and their ranks describes their position in this hierarchy. High-ranking taxa (e.g. those considered to be domains or kingdoms, for instance) include more sub-taxa than low-ranking taxa (e.g. those considered genera, species or subspecies). The rank of these taxa reflects inheritance of

BioCode that would regulate all taxon names,[4] but this attempt has so far failed[5] because of firmly entrenched traditions in each community.[6]

Consider a particular species, the

Eukarya
.

The

monophyletic groups of organisms), but this is required neither by the International Code of Zoological Nomenclature nor by the Botanical Code, and some experts on biological nomenclature do not think that this should be required,[8] and in that case, the hierarchy of taxa (hence, their ranks) does not necessarily reflect the hierarchy of clades
.

History

While older approaches to taxonomic classification were phenomenological, forming groups on the basis of similarities in appearance, organic structure and behavior, two important new methods developed in the second half of the 20th century changed drastically taxonomic practice. One is the advent of

Main ranks

In his landmark publications, such as the

Latin: dominium), introduced by Moore in 1974.[12][13]

Main taxonomic ranks
Latin English
regio domain
regnum kingdom
phylum phylum / 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. While not always used, some species include a subspecific epithet. For instance, modern humans are Homo sapiens sapiens, or H. sapiens sapiens.

In zoological nomenclature, higher taxon names are normally not italicized, but the

BioCode[4] and the PhyloCode[2]
all recommend italicizing all taxon names (of all ranks).

Ranks in zoology

There are rules applying to the following taxonomic ranks in the International Code of Zoological Nomenclature: superfamily, family, subfamily, tribe, subtribe, genus, subgenus, species, subspecies.[14]

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:[14]: §29–31 

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, which creates problems when naming taxa in these groups in speciose clades, such as

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. For this reason, Alain Dubois has been using the alternative expressions "nominal-series", "family-series", "genus-series" and "species-series" (among others) at least since 2000.[16][15]
)

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

Botanical ranks categorize organisms based (often) on their relationships (monophyly is not required by that clade, which does not even mention this word, nor that of "clade"). They start with Kingdom, then move to Division (or Phylum),[17] Class, Order, Family, Genus, and Species. Taxa at each rank generally possess shared characteristics and evolutionary history. Understanding these ranks aids in taxonomy and studying biodiversity.

Ranks in ICN[18]: CHAPTER III 
Rank Type Suffix
kingdom (regnum) primary
subregnum further
division (divisio)
phylum (phylum)
primary ‑phyta
-mycota (fungi)
subdivisio or subphylum further ‑phytina
-mycotina (fungi)
class (classis) primary ‑opsida (plant)
‑phyceae (algae)
-mycetes (fungi)
subclassis further ‑idae (plant)
‑phycidae (algae)
-mycetidae (fungi)
order (ordo) primary -ales
subordo further -ineae
family (familia) primary -aceae
subfamilia further ‑oideae
tribe (tribus) secondary -eae
subtribus further ‑inae
genus (genus) primary
subgenus further
section (sectio) secondary
subsectio further
series (series) secondary
subseries further
species (species) primary
subspecies further
variety (varietas) secondary
subvarietas further
form (forma) secondary
subforma further

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. (See also descriptive botanical name.)

Names of botanical taxa

Taxa at the rank of genus and above have a

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.[19]

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.[20]

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";[21] 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), 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 Pseudomonadati[22]
Phylum or division Arthropoda Chordata
Tracheophyta
)
Basidiomycota Pseudomonadota
Subphylum or subdivision Hexapoda Vertebrata Magnoliophytina (
Euphyllophytina
)
Agaricomycotina
Class Insecta Mammalia
Equisetopsida
)
Agaricomycetes Gammaproteobacteria
Subclass Pterygota Theria Rosidae (Magnoliidae) Agaricomycetidae
Superorder Panorpida Euarchontoglires
Order Diptera Primates Fabales Agaricales Enterobacterales
Suborder Brachycera
Haplorrhini
Family Drosophilidae
Hominidae
Fabaceae Amanitaceae Enterobacteriaceae
Subfamily Drosophilinae Homininae Faboideae Amanitoideae
Tribe Drosophilini Hominini Fabeae Escherichieae[23]
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 Viruses[25] Bacteria and Archaea[26] Embryophytes (Plants) Algae (Diaphoretickes) Fungi Animals
Realm -viria
Subrealm -vira
Kingdom -virae -ati[27]
Subkingdom -viretes
Division/phylum -viricota /vɪrəˈktə/ -ota[28] -ophyta[29] /ˈɒfətə, ə(ˈ)ftə/ -mycota /mˈktə/
Subdivision/subphylum -viricotina /vɪrəkəˈtnə/ -phytina[29] /fəˈtnə/ -mycotina /mkəˈtnə/
Class -viricetes /vɪrəˈstz/ -ia /iə/ -opsida /ˈɒpsədə/ -phyceae /ˈfʃ/ -mycetes /mˈstz/
Subclass -viricetidae /vɪrəˈsɛtəd/ -idae /əd/ -phycidae /ˈfɪsəd/ -mycetidae /mˈsɛtəd/
Superorder -anae /ˈn/
Order -virales /vˈrlz/ -ales /ˈlz/ -ida /ədə/ or -iformes /ə(ˈ)fɔːrmz/
Suborder -virineae /vəˈrɪn/ -ineae /ˈɪn/
Infraorder -aria /ˈɛəriə/
Superfamily -acea /ˈʃə/ -oidea /ˈɔɪdə/
Epifamily -oidae /ˈɔɪd/
Family -viridae /ˈvɪrəd/ -aceae /ˈʃ/ -idae /əd/
Subfamily -virineae /vɪˈrɪn/ -oideae /ˈɔɪd/ -inae /ˈn/
Infrafamily -odd /ɒd/[30]
Tribe -eae // -ini /ˈn/
Subtribe -inae /ˈn/ -ina /ˈnə/
Infratribe -ad[citation needed] /æd/ or -iti /ˈti/
Genus -virus
Subgenus -virus
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 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).
  • For animals, there are standard suffixes for taxa only up to the rank of superfamily.
    Nectaspida (Naraoiida)
    .
  • 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".
  • 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.[33]
  • In virology, the formal endings for taxa of
    viriforms are similar to viruses, only -vir- is replaced by -viroid-, -satellit- and -viriform-.[25] The extra levels of realm and subrealm end with -viria and -vira respectively.[25]

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 that applies.[citation needed]

The following is an artificial synthesis, solely for purposes of demonstration of absolute rank (but see notes), from most general to most specific:[34]

Significance and problems

Ranks are assigned based on subjective dissimilarity, and do not fully reflect the gradational nature of variation within nature. These problems were already identified by Willi Hennig, who advocated dropping them in 1969,[40] and this position gathered support from Graham C. D. Griffiths only a few years later.[41] In fact, these ranks were proposed in a fixist context and the advent of evolution sapped the foundations of this system, as was recognised long ago; the introduction of The Code of Nomenclature and Check-list of North American Birds Adopted by the American Ornithologists' Union published in 1886 states "No one appears to have suspected, in 1842 [when the Strickland code was drafted], that the Linnaean system was not the permanent heritage of science, or that in a few years a theory of evolution was to sap its very foundations, by radically changing men's conceptions of those things to which names were to be furnished."[42] Such ranks are used simply because they are required by the rank-based codes; because of this, some systematists prefer to call them nomenclatural ranks.[1][6] In most cases, higher taxonomic groupings arise further back in time, simply because the most inclusive taxa necessarily appeared first.[43] Furthermore, the diversity in some major taxa (such as vertebrates and angiosperms) is better known than that of others (such as fungi, arthropods and nematodes) not because they are more diverse than other taxa, but because they are more easily sampled and studied than other taxa, or because they attract more interest and funding for research.[44][45]

Of these many ranks, many systematists consider that the most basic (or important) is the species, but this opinion is not universally shared.[46][47][48] Thus, species are not necessarily more sharply defined than taxa at any other rank, and in fact, given the phenotypic gaps created by extinction, in practice, the reverse is often the case.[6] Ideally, a taxon is intended to represent a clade, that is, the phylogeny of the organisms under discussion, but this is not a requirement of the zoological and botanical codes.[6]

A classification in which all taxa have formal ranks cannot adequately reflect knowledge about phylogeny. Since taxon names are dependent on ranks in rank-based (Linnaean) nomenclature, taxa without ranks cannot be given names. Alternative approaches, such as phylogenetic nomenclature,[49][50] as implemented under the PhyloCode and supported by the International Society for Phylogenetic Nomenclature,[51] or using circumscriptional names, avoid this problem.[52][53] 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).

polyphyletic), as judged by a biologist, using all the information available to them. Equally ranked higher taxa in different phyla are not necessarily equivalent in terms of time of origin, phenotypic distinctiveness or number of lower-ranking included taxa (e.g., it is incorrect to assume that families of insects are in some way evolutionarily comparable to families of mollusks).[55][56][6] Of all criteria that have been advocated to rank taxa, age of origin has been the most frequently advocated. Willi Hennig proposed it in 1966,[9] but he concluded in 1969[40] that this system was unworkable and suggested dropping absolute ranks. However, the idea of ranking taxa using the age of origin (either as the sole criterion, or as one of the main ones) persists under the name of time banding, and is still advocated by several authors.[57][58][59][60] For animals, at least the phylum rank is usually associated with a certain body plan, which is also, however, an arbitrary criterion.[citation needed
]

Enigmatic taxa

Enigmatic taxa are taxonomic groups whose broader relationships are unknown or undefined.[61] (See Incertae sedis.)

Mnemonic

There are several acronyms intended to help memorise the taxonomic hierarchy, such as "King Phillip Came Over For Great Spaghetti".[62] (Kingdom(s), Phylum/Phyla, Class(es), Order(s), Family/Families, Genus, Species) (See taxonomy mnemonic.)

See also

Footnotes

  1. ^ The Virginia opossum is an exception.

References

  1. ^ .
  2. ^ .
  3. ^ "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". IAPT-Taxon.org. 2012. Articles 2 and 3. Archived from the original on 10 June 2019. Retrieved 28 April 2013.
  4. ^
    JSTOR 41059835
    .
  5. .
  6. ^ .
  7. ^ International Commission on Zoological Nomenclature (1999), International Code of Zoological Nomenclature. Fourth Edition, International Trust for Zoological Nomenclature, archived from the original on 21 May 2019, retrieved 12 April 2015
  8. .
  9. ^ .
  10. .
  11. .
  12. (PDF) from the original on 6 October 2016. Retrieved 5 October 2016.
  13. ^ Luketa, S. (2012). "New views on the megaclassification of life" (PDF). Protistology. 7 (4): 218–237. Archived from the original (PDF) on 2 April 2015.
  14. ^ from the original on 3 September 2021. Retrieved 10 November 2023.
  15. ^ .
  16. ^ Dubois, Alain (2000). "Synonymies and related lists in zoology: general proposals, with examples in herpetology". Dumerilia. 4 (2): 33–98.
  17. ^ jibran, jibran. "Log In ‹ Information metBotanical Ranks: Understanding Taxonomic Classification" Meta Description: Explore the hierarchical structure of botanical classification, from Kingdom to Species, essential for understanding plant diversity and evolution. a description — WordPress". dev-information-meta-descrition.pantheonsite.io. Retrieved 7 May 2024.
  18. ^ "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". IAPT-Taxon.org. 2012. Archived from the original on 10 October 2020. Retrieved 28 April 2013.
  19. ^ "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". IAPT-Taxon.org. 2012. Articles 4.2 and 24.1. Archived from the original on 3 August 2018. Retrieved 3 August 2018.
  20. ^ "International Code of Nomenclature for algae, fungi, and plants – Melbourne Code". IAPT-Taxon.org. 2012. Article 3.2, and Appendix 1, Articles H.1–3. Archived from the original on 10 October 2020. Retrieved 28 April 2013.
  21. ^ Stearn, W.T. 1992. Botanical Latin: History, grammar, syntax, terminology and vocabulary, Fourth edition. David and Charles.
  22. PMID 38252124
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  23. ^ "Tribe: Escherichieae". lpsn.dsmz.de. Retrieved 30 March 2025.
  24. ^ a b c d e "ICTV Code. Section 3.IV, § 3.23; section 3.V, §§ 3.27-3.28." International Committee on Taxonomy of Viruses. October 2018. Archived from the original on 6 July 2022. Retrieved 28 November 2018.
  25. PMID 37219928
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  27. .
  28. ^ a b "International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code)". IAPT-Taxon.org. 2018. Article 16. Archived from the original on 19 December 2018. Retrieved 19 December 2018.
  29. chelonian
    infrafamilies Chelodd (Gaffney & Meylan 1988: 169) and Baenodd (ibid., 176).
  30. ^ ICZN article 29.2
  31. ^ Pearse, A.S. (1936) Zoological names. A list of phyla, classes, and orders, prepared for section F, American Association for the Advancement of Science. Archived 15 November 2021 at the Wayback Machine American Association for the Advancement of Science, p. 4
  32. ^ As supplied by Gaffney & Meylan (1988).
  33. ^ For the general usage 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).
  34. ISSN 0932-4739
    .
  35. ^ a b c d 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 Archived 16 January 2019 at the Wayback Machine (2005).
  36. ^ a b c d 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 Archived 16 January 2019 at the Wayback Machine 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.
  37. ^ a b c d e 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.
  38. 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.
  39. ^ a b Hennig, Willi (1969). Die Stammesgeschichte der Insekten. Frankfurt am Main: Kramer. p. 436.
  40. JSTOR 2412942
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  41. ^ American Ornithologists' Union (1886). The Code of Nomenclature and Check-list of North American Birds Adopted by the American Ornithologists' Union; Being the Report of the Committee of the Union on Classification and Nomenclature. pp. viii + 392.
  42. .
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  51. ^ 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.
  52. .
  53. ^ Stuessy, T.F. (2009). Plant Taxonomy: The Systematic Evaluation of Comparative Data. 2nd ed. Columbia University Press, p. 175.
  54. ^ a b Brusca, R.C. & Brusca, G.J. (2003). Invertebrates. 2nd ed. Sunderland, Massachusetts: Sinauer Associates, pp. 26–27.
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  61. from the original on 23 November 2023. Retrieved 23 November 2023.

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