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{{short description|Taxonomic rank}} |
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{{Biological classification}} |
{{Biological classification}} |
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In [[biology]], a '''kingdom''' is the second highest [[taxonomic rank]], just below [[Domain (biology)|domain]]. Kingdoms are divided into smaller groups called [[Phylum|phyla]] (singular phylum). |
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In [[Biology|biological]] [[taxonomy]], ''kingdom''' and/or '''regnum''' is a [[taxonomic rank]] in either (historically) the highest rank, or (in the new [[three-domain system]]) the [[Rank (zoology)|rank]] below [[domain (biology)|domain]]. Each kingdom is divided into smaller groups called [[Phylum|phyla]] (or in some contexts these are called "divisions"). Currently, many textbooks from the United States use a system of six kingdoms ([[Animal]]ia, [[Plantae]], [[Fungi]], [[Protista]], [[Archaea]], [[Bacteria]]) while British and Australian textbooks may describe five kingdoms ([[Animalia]], [[Plantae]], [[Fungi]], [[Protista]], and [[Prokaryota]] or [[Monera]]). The classifications of taxonomy are [[life]], [[domain (biology)|domain]], kingdom, [[phylum]], [[class (biology)|class]], [[order (biology)|order]], [[family (biology)|family]], [[genus]], and [[species]]. |
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Traditionally, textbooks from Canada and the United States have used a system of [[#Six kingdoms|six kingdoms]] ([[Animal]]ia, [[Plant]]ae, [[Fungus|Fungi]], [[Protist]]a, [[Archaea]]/Archaebacteria, and [[Bacteria]] or Eubacteria), while textbooks in other parts of the world, such as Bangladesh, Brazil, Greece, India, Pakistan, Spain, and the United Kingdom have used [[#Five kingdoms|five kingdoms]] (Animalia, Plantae, Fungi, Protista and [[Monera]]). |
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==Early concepts== |
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[[Carolus Linnaeus]] distinguished two kingdoms of living things: Animalia for [[animal]]s and Vegetabilia for [[plant]]s (Linnaeus also included [[mineral]]s, placing them in a third kingdom, [[Mineralia]]). Linnaeus divided each kingdom into classes, later grouped into [[phylum|phyla]] for animals and [[Division (biology)|divisions]] for plants. It gradually became apparent how important the prokaryote/eukaryote distinction is, and Stanier and van Niel popularized [[Édouard Chatton]]'s proposal in the 1960s to divide them.<ref name="Stanier">{{cite journal | author = R. Y. Stanier and C. B. van Niel | year = 1962 | title = The concept of a bacterium | journal = Arch. Microbiol. | volume = 42 | pages = 17–35 }}</ref> |
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Some recent classifications based on modern [[cladistics]] have explicitly abandoned the term ''kingdom'', noting that some traditional kingdoms are not [[Monophyly|monophyletic]], meaning that they do not consist of all the [[Lineal descendant|descendants]] of a common [[ancestor]]. The terms ''[[flora]]'' (for plants), ''[[fauna]]'' (for animals), and, in the 21st century, ''[[funga]]'' (for fungi) are also used for life present in a particular region or time.<ref>{{Cite web|url=https://www.iucn.org/sites/dev/files/statement-3f.pdf|title=IUCN SSC acceptance of Fauna Flora Funga|publisher=Fungal Conservation Committee, IUCN SSC|date=2021|quote=The IUCN Species Survival Commission calls for the due recognition of fungi as major components of biodiversity in legislation and policy. It fully endorses the Fauna Flora Funga Initiative and asks that the phrases '''animals and plants''' and '''fauna and flora''' be replaced with '''animals, fungi, and plants''' and '''fauna, flora, and funga'''.|access-date=2022-03-04|archive-date=2021-11-11|archive-url=https://web.archive.org/web/20211111141833/https://www.iucn.org/sites/dev/files/statement-3f.pdf|url-status=dead}}</ref><ref>{{Cite web |title=Re:wild and IUCN SSC become first global organizations to call for the recognition of fungi as one of three kingdoms of life critical to protecting and restoring Earth |author= |website=International Union for Conservation of Nature (IUCN) |date=3 August 2021 |url= https://www.iucn.org/news/species-survival-commission/202108/rewild-and-iucn-ssc-become-first-global-organizations-call-recognition-fungi-one-three-kingdoms-life-critical-protecting-and-restoring-earth}}</ref> |
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[[Cladistics]] does not use this term, because one of the fundamental premises of cladistics is that the evolutionary tree is so deep and so complex that it is inadvisable to set a fixed number of levels. |
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== Definition and associated terms == |
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==Five kingdoms== <!-- This section is linked from [[Monera]] --> |
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When [[Carl Linnaeus]] introduced the rank-based system of [[nomenclature]] into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: [[class (biology)|class]], [[order (biology)|order]], [[genus]] and [[species]].<ref>{{cite book |author=Linnaeus, C. |title=Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species |year=1735}}</ref> Later two further main ranks were introduced, making the sequence kingdom, [[phylum|phylum or division]], [[class (biology)|class]], [[order (biology)|order]], [[family (biology)|family]], [[genus]] and [[species]].<ref>See e.g. {{cite conference |year=2006 |editor-last=McNeill |editor-first=J. |display-editors=etal |title=International Code of Botanical Nomenclature (Vienna Code) adopted by the Seventeenth International Botanical Congress, Vienna, Austria, July 2005 |edition=electronic |location=Vienna |publisher=International Association for Plant Taxonomy |url=http://ibot.sav.sk/icbn/main.htm |access-date=2011-02-20 |archive-url=https://web.archive.org/web/20121006231936/http://ibot.sav.sk/icbn/main.htm |archive-date=6 October 2012}}, {{cite web |url=http://ibot.sav.sk/icbn/no%20frames/0007Ch1Art003.htm |title=article 3.1}}</ref> In 1990, the rank of [[domain (biology)|domain]] was introduced above kingdom.<ref name=Woese/> |
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[[Robert Whittaker]] recognized an additional kingdom for the [[Fungus|Fungi]]. The resulting '''five-kingdom system''', proposed in 1969, has become a popular standard and with some refinement is still used in many works and forms the basis for newer multi-kingdom systems. It is based mainly on differences in [[nutrition]]; his Plantae were mostly multicellular [[autotroph]]s, his Animalia multicellular [[heterotroph]]s, and his Fungi multicellular [[saprotroph]]s. The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies.<ref name="Whittaker1969">{{cite journal |author=Whittaker RH |title=New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms |journal=Science (journal) |volume=163 |issue=863 |pages=150–60 |year=1969 |month=January |pmid=5762760 |doi=10.1126/science.163.3863.150 |url=}}</ref> |
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Prefixes can be added so ''subkingdom'' (''subregnum'') and ''infrakingdom'' (also known as ''infraregnum'') are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain. In some classification systems the additional rank ''branch'' (Latin: ''ramus'') can be inserted between subkingdom and infrakingdom, e.g., [[Protostomia]] and [[Deuterostomia]] in the classification of Cavalier-Smith.<ref name="Cavalier-Smith 1998 203–66">{{cite journal |last=Cavalier-Smith |first=T. |year=1998 |title=A revised six-kingdom system of life |journal=[[Biological Reviews]] |volume=73 |pages=203–66 |url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=685 |issue=3 |doi=10.1111/j.1469-185X.1998.tb00030.x |pmid=9809012|s2cid=6557779 |url-access=subscription }}</ref> |
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==Six kingdoms==<!-- This section is linked from [[Monera]] --> |
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In the years around 1980, there was an emphasis on phylogeny and redefining the kingdoms to be monophyletic groups, groups made up of relatively closely related organisms. The Animalia, Plantae, and Fungi were generally reduced to core groups of closely related forms, and the others placed into the Protista. Based on [[RNA]] studies, [[Carl Woese]] divided the prokaryotes (Kingdom [[Monera]]) into two kingdoms, called [[bacterium|Eubacteria]] and [[Archaea|Archaebacteria]]. Carl Woese attempted to establish a Three Primary Kingdom (or Urkingdom) system in which Plants, Animals, Protista, and Fungi were lumped into one primary kingdom of all eukaryotes. The Eubacteria and Archaebacteria made up the other two urkingdoms. The initial use of "six Kingdom systems" represents a blending of the classic Five Kingdom system and Woese's [[Three-domain system|Three Domain system]]. Such '''six Kingdom systems''' have become standard in many works.<ref name="Woese1977">{{cite journal |author=Balch WE, Magrum LJ, Fox GE, Wolfe RS, Woese CR |title=An ancient divergence among the bacteria |journal=J. Mol. Evol. |volume=9 |issue=4 |pages=305–11 |year=1977 |month=August |pmid=408502 |doi=10.1007/BF01796092 |url=}}</ref> |
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== History == |
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A variety of new eukaryotic kingdoms were also proposed, but most were quickly invalidated, ranked down to phyla or classes, or abandoned. The only one which is still in common use is the kingdom [[Chromista]] proposed by [[Thomas Cavalier-Smith|Cavalier-Smith]], including organisms such as [[kelp]], [[diatom]]s, and [[water mould]]s. Thus the eukaryotes are divided into three primarily heterotrophic groups, the Animalia, Fungi, and Protozoa, and two primarily photosynthetic groups, the Plantae (including [[red alga|red]] and [[green alga]]e) and Chromista. However, it has not become widely used because of uncertainty over the monophyly of the latter two kingdoms. |
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===Two kingdoms of life=== |
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{{anchor|Three kingdoms: animal, vegetable, and mineral}} |
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The classification of living things into animals and plants is an ancient one. [[Aristotle]] (384–322 BC) classified animal species in his ''[[History of Animals]]'', while his pupil [[Theophrastus]] ({{circa|371}}–{{circa|287 BC}}) wrote a parallel work, the ''[[Historia Plantarum (Theophrastus)|Historia Plantarum]]'', on plants.<ref>{{cite book |last=Singer |first=Charles J. |year=1931 |title=A short history of biology, a general introduction to the study of living things |location=Oxford |publisher=Clarendon Press |oclc=1197036 }}</ref> |
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[[Carl Linnaeus]] (1707–1778) laid the foundations for modern [[biological nomenclature]], now regulated by the [[Nomenclature Codes]], in 1735. He distinguished two kingdoms of living things: ''Regnum Animale'' ('[[animal]] kingdom') and ''Regnum Vegetabile'' ('vegetable kingdom', for [[plant]]s). Linnaeus also included [[mineral]]s in his [[Classification (biology)|classification system]], placing them in a third kingdom, ''[[Mineralia|Regnum Lapideum]]''. |
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Woese stresses genetic similarity over outward appearances and behaviour, relying on comparisons of ribosomal RNA genes at the molecular level to sort out classification categories. A plant does not look like an animal, but at the cellular level, both groups are eukaryotes, having similar subcellular organization, including cell nuclei, which the Eubacteria and Archaebacteria do not have. More importantly, plants, animals, fungi, and protists are more similar to each other in their genetic makeup at the molecular level, based on RNA studies, than they are to either the Eubacteria or Archaebacteria. Woese also found that all of the eukaryotes, lumped together as one group, are more closely related, genetically, to the Archaebacteria than they are to the Eubacteria. This means that the Eubacteria and Archaebacteria are separate groups even when compared to the eukaryotes. So, Woese established the [[Three-domain system]], clarifying that all the Eukaryotes are more closely genetically related compared to their genetic relationship to either the bacteria or the archaebacteria, without having to replace the "six kingdom systems" with a three kingdom system. The Three Domain system is a "six kingdom system" that unites the eukaryotic kingdoms into the Eukarya Domain based on their relative genetic similarity when compared to the Bacteria Domain and the Archaea Domain. Woese also recognized that the Protista Kingdom is not a monophyletic group and might be further divided at the level of Kingdom. Others have divided the Protista Kingdom into the Protozoa and the Chromista, for instance. |
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{{clade |
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==Recent advances== |
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|label1=   |
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Kingdom classification is in flux due to ongoing research and discussion. As new findings and technologies become available they allow the refinement of the model. For example, gene sequencing techniques allow the comparison of the genome of different groups ([[Phylogenomics]]). A study published in 2007 by Fabien Burki, ''et al.''<ref>{{cite journal |author=Burki F, Shalchian-Tabrizi K, Minge M, ''et al.'' |title=Phylogenomics reshuffles the eukaryotic supergroups |journal=PLoS ONE |volume=2 |issue=8 |pages=e790 |year=2007 |pmid=17726520 |pmc=1949142 |doi=10.1371/journal.pone.0000790 |url=}}</ref> proposes four high level groups of [[eukaryotes]] based on phylogenomics research. |
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|1={{clade |
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# [[Plantae]] (green and red algae, and plants) |
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|label1= Life |
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# [[Unikont]]a (amoebas, fungi, and animals) |
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|1={{clade |
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# [[Excavata]] (free-living and parasitic [[protist]]s) |
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|2=Regnum Vegetabile ('vegetables'/plants) |
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# [[SAR supergroup|SAR]] (acronym for [[Stramenopile]]s, [[Alveolate]]s, and [[Rhizaria]]–the names of some of its members. Burki found that the previously split groups Rhizaria and [[Chromalveolate]]s were more similar in 123 common genes than once thought.) |
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|1=Regnum [[Animal]]e (animals) |
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Completing this 6 kingdom model would be: |
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}} |
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:[[Bacteria]] |
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|label2= Non-life |
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:[[Archaea]] |
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|2={{clade |
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Upcoming results from [[phylogenetic]] studies may yet again make this model obsolete and expand the kingdom classifications to 18 and upwards to even 30 separate kingdoms. {{Citation needed|date=September 2009}} |
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|1=Regnum Lapideum (minerals) |
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}} |
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}} |
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}} |
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=== Three kingdoms of life === |
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==Summary== |
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{{anchor|Three kingdoms: plants, protists, and animals}} |
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{| rules="all" style="border: 1px solid #999"cellspacing="0" cellpadding="5" align="center" |
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|----- |
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{{further|Tree of life (biology)}} |
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! [[Linnaeus]]<ref name="Linnaeus1735">{{cite journal | author =C. Linnaeus | title = Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species | journal = | volume = | pages = | year = 1735 | doi = }}</ref><br />(1735)<br />2 kingdoms |
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! [[Ernst Haeckel|Haeckel]]<ref name="Haeckel1866">{{cite journal | author = Haeckel | title = Generelle Morphologie der Organismen. Reimer, Berlin.| year = 1866 | doi = }}</ref><br />(1866)<br />3 kingdoms |
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[[File:Haeckel arbol bn.png|thumb|upright=1.5|right|Haeckel's original (1866) conception of the three kingdoms of life, including the new kingdom Protista. Notice the inclusion of the cyanobacterium ''[[Nostoc]]'' with plants.]] |
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! [[Édouard Chatton|Chatton]]<ref name="Chatton1925">{{cite journal | author = E. Chatton | title = Pansporella perplexa. Réflexions sur la biologie et la phylogénie des protozoaires | journal = Ann. Sci. Nat. Zool | volume = 10-VII | pages = 1–84| year = 1925| doi = }}</ref><br />(1925)<br />2 groups |
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In 1674, [[Antonie van Leeuwenhoek]], often called the "father of microscopy", sent the [[Royal Society]] of London a copy of his first observations of microscopic single-celled organisms. Until then, the existence of such microscopic organisms was entirely unknown. Despite this, Linnaeus did not include any microscopic creatures in his original taxonomy. |
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! [[Herbert Copeland|Copeland]]<ref name="Copeland1938">{{cite journal | author = H. Copeland | title = The kingdoms of organisms | journal = Quarterly review of biology | volume = 13 | pages = 383–420 | year = 1938 | doi = 10.1086/394568 }}</ref><br />(1938)<br />4 kingdoms |
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! [[Robert Whittaker|Whittaker]]<ref name="Whittaker1969">{{cite journal | author = R. H. Whittaker | year = 1969 | title = New concepts of kingdoms of organisms | journal = Science | volume = 163 | pages = 150–160 | doi = 10.1126/science.163.3863.150 <!--Retrieved from CrossRef by DOI bot-->}}</ref> |
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At first, microscopic organisms were classified within the animal and plant kingdoms. However, by the mid–19th century, it had become clear to many that "the existing dichotomy of the plant and animal kingdoms [had become] rapidly blurred at its boundaries and outmoded".<ref name=Scamardella1999>{{cite journal |last=Scamardella |first=Joseph M. |year=1999 |title=Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista |journal=[[International Microbiology]] |volume=2 |pages=207–16 |pmid=10943416 |issue=4 }}</ref> |
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(1969)<br />5 kingdoms |
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! [[Carl Woese|Woese]] <ref name="Woese1977b">{{cite journal |author=Woese CR, Fox GE |title=Phylogenetic structure of the prokaryotic domain: the primary kingdoms |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=74 |issue=11 |pages=5088–90 |year=1977 |month=November |pmid=270744 |pmc=432104 |doi= |url=}}</ref><ref name="Woese1990">{{cite journal |author=Woese CR, Kandler O, Wheelis ML |title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=87 |issue=12 |pages=4576–9 |year=1990 |month=June |pmid=2112744 |pmc=54159 |doi= |url=}}</ref><br />(1977,1990)<br />3 domains |
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In 1860 [[John Hogg (biologist)|John Hogg]] proposed the ''Protoctista'', a third kingdom of life composed of "all the lower creatures, or the primary organic beings"; he retained Regnum Lapideum as a fourth kingdom of minerals.<ref name=Scamardella1999/> In 1866, [[Ernst Haeckel]] also proposed a third kingdom of life, the ''[[Protista]]'', for "neutral organisms" or "the kingdom of primitive forms", which were neither animal nor plant; he did not include the Regnum Lapideum in his scheme.<ref name=Scamardella1999/> Haeckel revised the content of this kingdom a number of times before settling on a division based on whether organisms were unicellular (Protista) or multicellular (animals and plants).<ref name=Scamardella1999/> |
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|----- |
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| bgcolor="pink" | '''[[Animalia]]''' |
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{{clade |
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| bgcolor="pink" | '''[[Animalia]]''' |
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|label1=   |
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| rowspan="5" bgcolor="e0d0b0" | '''[[Eukaryote]]''' |
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|1={{clade |
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| bgcolor="pink" | '''[[Animalia]]''' |
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|label1= Life |
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| bgcolor="pink" | '''[[Animalia]]''' |
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|1={{clade |
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| rowspan="5" bgcolor="e0d0b0" | '''[[Eukarya]]'''<!-- Eukarya --> |
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|1=Kingdom [[Protista]] or Protoctista |
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|----- |
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|2=Kingdom [[Plantae]] |
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| rowspan="3" bgcolor="lightgreen" | '''[[Vegetabilia]]'''<!-- Plantae --> |
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|3=Kingdom [[Animalia]] |
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| rowspan="3" bgcolor="lightgreen" | '''[[Plantae]]'''<!-- Plantae --> |
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}} |
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| bgcolor="lightgreen" | '''[[Plantae]]'''<!-- Plantae --> |
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|label2= Non-life |
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| bgcolor="lightgreen" | '''[[Plantae]]'''<!-- Plantae --> |
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|2={{clade |
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<!-- Eukarya --> |
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|1=Regnum Lapideum (minerals) |
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|----- |
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}} |
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| rowspan="3" bgcolor="Khaki" | '''[[Protoctista]]'''<!-- Protista --> |
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}} |
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| bgcolor="lightblue" | '''[[Fungi]]''' |
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}} |
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<!-- Eukarya --> |
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|----- |
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=== Four kingdoms === |
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| rowspan="2" bgcolor="khaki" | '''[[Protista]]'''<!-- Protista --> |
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The development of [[microscopy]] revealed important distinctions between those organisms whose cells do not have a distinct [[Cell nucleus|nucleus]] ([[prokaryote]]s) and organisms whose cells do have a distinct nucleus ([[eukaryote]]s). In 1937 [[Édouard Chatton]] introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms.<ref name=sapp2005/> |
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<!-- Eukarya --> |
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|----- |
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In 1938, [[Herbert Copeland (biologist)|Herbert F. Copeland]] proposed a four-kingdom classification by creating the novel Kingdom [[Monera]] of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as [[Bacteria]] and [[Archaea]]. Ernst Haeckel, in his 1904 book ''The Wonders of Life'', had placed the blue-green algae (or Phycochromacea) in Monera; this would gradually gain acceptance, and the blue-green algae would become classified as bacteria in the phylum [[Cyanobacteria]].<ref name=Scamardella1999/><ref name=sapp2005>{{Cite journal |last1=Sapp |first1=J. | author-link1=Jan Sapp |title=The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology |doi=10.1128/MMBR.69.2.292-305.2005 |journal=[[Microbiology and Molecular Biology Reviews]] |volume=69 |issue=2 |pages=292–305 |year=2005 |pmid=15944457 |pmc=1197417}}</ref> |
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| rowspan="3" bgcolor="white" | ''(not treated)'' |
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| rowspan="3" bgcolor="khaki" | '''[[Protista]]''' |
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In the 1960s, [[Roger Stanier]] and [[C. B. van Niel]] promoted and popularized Édouard Chatton's earlier work, particularly in their paper of 1962, "The Concept of a Bacterium"; this created, for the first time, a rank above kingdom—a ''superkingdom'' or ''empire''—with the [[two-empire system]] of prokaryotes and eukaryotes.<ref name=sapp2005/> The two-empire system would later be expanded to the [[Domain (biology)|three-domain system]] of Archaea, Bacteria, and Eukaryota.<ref name="Stanier">{{cite journal |last1=Stanier |first1=R.Y. |last2=Van Neil |first2=C.B. |year=1962 |title=The concept of a bacterium |journal=[[Archiv für Mikrobiologie]] |volume=42 |issue=1 |pages=17–35 |pmid=13916221 |name-list-style=amp |doi=10.1007/BF00425185 |s2cid=29859498 }}</ref> |
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<!-- Protista --> |
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<!-- Protista --> |
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{{clade |
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<!-- Eukarya --> |
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|label1= Life |
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|----- |
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|1={{clade |
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| rowspan="2" bgcolor="lightgrey" | '''[[Prokaryote]]''' |
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|label1=Empire [[Prokaryota]] |
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| rowspan="2" bgcolor="lightgrey" | '''[[Monera]]''' |
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|1={{clade |
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| rowspan="2" bgcolor="lightgrey" | '''[[Monera]]''' |
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|1=Kingdom [[Monera]] |
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| bgcolor="darkgray" | '''[[Archaea]]''' |
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}} |
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|----- |
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|label2=Empire [[Eukaryota]] |
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| bgcolor="lightgrey" | '''[[Bacteria]]''' |
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|2={{clade |
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<!-- Prokaryotes --> |
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|1=Kingdom [[Protista]] or Protoctista |
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<!-- Bactéries --> |
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|2=Kingdom [[Plantae]] |
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|3=Kingdom [[Animalia]] |
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}} |
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}} |
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}} |
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=== Five kingdoms === |
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{{anchor|Five kingdoms}} |
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The differences between [[fungi]] and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification,<ref name=Scamardella1999/> but was largely ignored in this separation by scientists of his time. [[Robert Whittaker (ecologist)|Robert Whittaker]] recognized an additional kingdom for the [[Fungus|Fungi]].<ref name="Whittaker5">{{cite journal |last=Whittaker |first=R.H. |date=January 1969 |title=New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms |journal=[[Science (journal)|Science]] |volume=163 |issue=3863 |pages=150–60 |pmid=5762760 |doi=10.1126/science.163.3863.150|bibcode = 1969Sci...163..150W |citeseerx=10.1.1.403.5430 }}</ref> The resulting five-kingdom system, proposed in 1969 by Whittaker, has become a popular standard and with some refinement is still used in many works and forms the basis for new multi-kingdom systems. It is based mainly upon differences in [[nutrition]]; his Plantae were mostly multicellular [[autotroph]]s, his Animalia multicellular [[heterotroph]]s, and his Fungi multicellular [[saprotroph]]s. |
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The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies.<ref name="Whittaker5"/> The five kingdom system may be combined with the two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as [[Lynn Margulis]]'s system of five kingdoms, the plants included just the land plants ([[Embryophyte|Embryophyta]]), and Protoctista has a broader definition.<ref>{{Cite book |url=https://books.google.com/books?id=9IWaqAOGyt4C |title=Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth |last1=Margulis |first1=Lynn |last2=Chapman |first2=Michael J. |name-list-style=vanc |date=2009-03-19 |publisher=[[Academic Press]] |isbn=9780080920146 |via=[[Google Books]]}}</ref>{{Page needed|date=May 2024}} |
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Following publication of Whittaker's system, the five-kingdom model began to be commonly used in high school biology textbooks.<ref name="Emily Case"/> But despite the development from two kingdoms to five among most scientists, some authors as late as 1975 continued to employ a traditional two-kingdom system of animals and plants, dividing the plant kingdom into subkingdoms Prokaryota (bacteria and cyanobacteria), Mycota (fungi and supposed relatives), and Chlorota (algae and land plants).<ref>{{cite book |last1=Palmer |first1=E. Laurence |last2=Fowler |first2=Seymour H. |date=January 1975 |title=Fieldbook of Natural History |edition=2nd |url=https://archive.org/details/fieldbookofnatur00palm |publisher=[[McGraw-Hill]] |isbn=978-0-070-48425-2 |url-access=registration}}</ref> |
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{{clade |
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|label1= Life |
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|1={{clade |
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|label1=Empire [[Prokaryota]] |
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|1={{clade |
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|1=Kingdom [[Monera]] |
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}} |
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|label2=Empire [[Eukaryota]] |
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|2={{clade |
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|1=Kingdom [[Protista]] or Protoctista |
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|2=Kingdom [[Plantae]] |
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|3=Kingdom [[Fungi]] |
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|4=Kingdom [[Animalia]] |
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}} |
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}} |
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}} |
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{| role="presentation" class="wikitable mw-collapsible" |
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|+ {{nowrap|Whittaker's five kingdom system (1969)<ref name="Whittaker5"/>}} |
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|-style="font-size: 87%;vertical-align: top;background: white" |
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|| |
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'''Kingdom [[Monera]]''' |
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*Branch Myxomonera |
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**Phylum [[Cyanophyta]] |
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**Phylum Myxobacteriae |
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*Branch Mastigomonera |
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**Phylum Eubacteriae |
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**Phylum [[Actinomycota]] |
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**Phylum [[Spirochaetae]] |
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|| |
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'''Kingdom [[Protista]]''' |
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*Phylum [[Euglenophyta]] |
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*Phylum [[Chrysophyta]] |
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*Phylum [[Pyrrophyta]] |
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*Phylum [[Hyphochytridiomycota]] |
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*Phylum [[Plasmodiophoromycota]] |
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*Phylum [[Sporozoa]] |
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*Phylum [[Cnidosporidia]] |
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*Phylum [[Zoomastigina]] |
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*Phylum [[Sarcodina]] |
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*Phylum [[Ciliophora]] |
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|| |
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'''Kingdom [[Plantae]]''' |
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*Subkingdom [[Rhodophyta|Rhodophycophyta]] |
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**Phylum [[Rhodophyta]] |
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*Subkingdom [[Phaeophyta|Phaeophycophyta]] |
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**Phylum [[Phaeophyta]] |
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*Subkingdom [[Viridiplantae|Euchlorophyta]] |
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**Branch [[Green algae|Chlorophycophyta]] |
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***Phylum [[Chlorophyta]] |
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***Phylum [[Charophyta]] |
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**Branch [[Embryophyta|Metaphyta]] |
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***Phylum [[Moss|Bryophyta]] |
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***Phylum [[Tracheophyta]] |
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|| |
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'''Kingdom [[Fungi]]''' |
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*Subkingdom Gymnomycota |
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**Phylum [[Mycetozoa|Myxomycota]] |
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**Phylum [[Acrasiomycota]] |
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**Phylum [[Labyrinthulomycota]] |
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*Subkingdom Dimastigomycota |
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**Phylum [[Oomycota]] |
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*Subkingdom [[Eumycota]] |
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**Branch Opisthomastigomycota |
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***Phylum [[Chytridiomycota]] |
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**Branch [[Amastigomycota]] |
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***Phylum [[Zygomycota]] |
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***Phylum [[Ascomycota]] |
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***Phylum [[Basidiomycota]] |
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|| |
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'''Kingdom [[Animalia]]''' |
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*Subkingdom Agnotozoa |
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**Phylum [[Mesozoa]] |
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*Subkingdom Parazoa |
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**Phylum [[Porifera]] |
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**Phylum [[Archaeocyatha]] {{extinct}} |
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*Subkingdom [[Eumetazoa]] |
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**Branch [[Radiata]] |
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***Phylum [[Cnidaria]] |
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***Phylum [[Ctenophora]] |
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**Branch [[Bilateria]] |
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***Grade [[Acoelomata]] |
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****Phylum [[Platyhelminthes]] |
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****Phylum [[Nemertea]] or Rhynchocoela |
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***Grade [[Pseudocoelomata]] |
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****Phylum [[Acanthocephala]] |
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****Phylum [[Aschelminthes]] |
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****Phylum [[Entoprocta]] or [[Kamptozoa]] |
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***Grade [[Coelomata]] |
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****Subgrade [[Protostome|Schizocoela]] |
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*****Phylum [[Bryozoa]] or [[Ectoprocta]] |
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*****Phylum [[Brachiopoda]] |
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*****Phylum [[Phoronida]] |
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*****Phylum [[Mollusca]] |
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*****Phylum [[Sipunculoidea]] |
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*****Phylum [[Echiuroidea]] |
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*****Phylum [[Annelida]] |
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*****Phylum [[Arthropoda]] |
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****Subgrade [[Deuterostome|Enterocoela]] |
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*****Phylum Brachiata or [[Pogonophora (worm)|Pogonophora]] |
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*****Phylum [[Chaetognatha]] |
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*****Phylum [[Echinodermata]] |
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*****Phylum [[Hemichordata]] |
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*****Phylum [[Chordata]] |
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|} |
|} |
||
=== Six kingdoms === |
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Note that the equivalences in this table are not perfect. e.g. Haeckel placed the [[red algae]] (Haeckel's Florideae; modern [[Florideophyceae]]) and [[blue-green algae]] (Haeckel's Archephyta; modern [[Cyanobacteria]]) in his Plantae. |
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In 1977, [[Carl Woese]] and colleagues proposed the fundamental subdivision of the prokaryotes into the Eubacteria (later called the Bacteria) and Archaebacteria (later called the Archaea), based on [[ribosomal RNA]] structure;<ref name="Balch_Magrum_Fox_Wolfe_Woese"/> this would later lead to the proposal of [[#Three domains of life|three "domains" of life]], of Bacteria, Archaea, and Eukaryota.<ref name="Woese"/> Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea.<ref>{{Cite web |title=The Six Kingdoms |url=http://www.ric.edu/faculty/ptiskus/six_kingdoms/index.htm |access-date=2020-07-25 |website=www.ric.edu |publisher=[[Rhode Island College]] |archive-date=2021-05-10 |archive-url=https://web.archive.org/web/20210510010016/http://www.ric.edu/faculty/ptiskus/Six_Kingdoms/Index.htm |url-status=dead }}</ref> This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus.<ref name="Emily Case">{{Cite journal |last=Case |first=Emily |date=2008-10-01 |title=Teaching Taxonomy: How Many Kingdoms? |url=https://eric.ed.gov/?id=EJ813862 |access-date=2020-07-28 |journal=[[American Biology Teacher]] |volume=70 |issue=8 |pages=472–477 |doi=10.2307/30163328 |jstor=30163328 |language=en|url-access=subscription }}</ref> But the division of prokaryotes into two kingdoms remains in use with the recent [[#Seven kingdoms|seven kingdoms]] scheme of Thomas Cavalier-Smith, although it primarily differs in that Protista is replaced by [[Protozoa]] and [[Chromista]].<ref name="Cavalier-Smith 2015"/> |
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{{clade |
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In 1998, [[Cavalier-Smith]]<ref name="Cavalier-Smith1998">{{cite journal |author=Cavalier-Smith T |title=A revised six-kingdom system of life |journal=Biol Rev Camb Philos Soc |volume=73 |issue=3 |pages=203–66 |year=1998 |month=August |pmid=9809012 |doi=10.1111/j.1469-185X.1998.tb00030.x |url=}}</ref> proposed that Protista should be divided into 2 new kingdoms: [[Chromista]] the phylogenetic group of golden-brown algae that includes those algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them, and [[Protozoa]], the kingdom of protozoans<ref name="Cavalier-Smith2006">{{cite journal | author = T. Cavalier-Smith | title = Protozoa: the most abundant predators on earth | journal = Microbiology Today (pdf [http://www.sgm.ac.uk/pubs/micro_today/pdf/110605.pdf here])| volume = | pages = 166–167 | year = 2006 | doi = }}</ref>. This proposal has not been widely-adopted, although the question of the relationships between different domains of life remains controversial.<ref>{{cite journal |author=Walsh DA, Doolittle WF |title=The real 'domains' of life |journal=Curr. Biol. |volume=15 |issue=7 |pages=R237–40 |year=2005 |month=April |pmid=15823519 |doi=10.1016/j.cub.2005.03.034}}</ref> |
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|label1= Life |
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|1={{clade |
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|1={{clade |
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|label1=Domain [[Prokaryote|Prokaryota]] |
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|1={{clade |
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|1=Kingdom [[Eubacteria]] (Bacteria) |
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|2=Kingdom [[Archaebacteria]] (Archaea) |
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}} |
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}} |
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|2={{clade |
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|label1=Domain [[Eukaryote|Eukaryota]] |
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|1={{clade |
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|1=Kingdom [[Protista]] or Protoctista |
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|2=Kingdom [[Plant]]ae |
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|3=Kingdom [[Fungus|Fungi]] |
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|4=Kingdom [[Animal]]ia |
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}} |
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}} |
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}} |
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}} |
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=== Eight kingdoms === |
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{| |
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[[Thomas Cavalier-Smith]] supported the consensus at that time, that the difference between [[Eubacteria]] and [[Archaebacteria]] was so great (particularly considering the genetic distance of ribosomal genes) that the prokaryotes needed to be separated into two different kingdoms. He then divided [[Eubacteria]] into two subkingdoms: [[Negibacteria]] ([[Gram-negative bacteria]]) and [[Posibacteria]] ([[Gram-positive bacteria]]). Technological advances in electron microscopy allowed the separation of the [[Chromista]] from the [[Plantae]] kingdom. Indeed, the chloroplast of the chromists is located in the lumen of the [[endoplasmic reticulum]] instead of in the [[cytosol]]. Moreover, only chromists contain [[chlorophyll c]]. Since then, many non-photosynthetic phyla of protists, thought to have secondarily lost their chloroplasts, were integrated into the kingdom Chromista. |
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|----- |
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! Empires |
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Finally, some protists lacking mitochondria were discovered.<ref>{{cite journal |last=Cavalier-Smith |first=Thomas |date=March 26, 1987 |title=Eucaryotes with no mitochondria |journal=[[Nature (journal)|Nature]] |volume=326 |issue=6111 |pages=332–333 |doi=10.1038/326332a0 |pmid=3561476 |bibcode=1987Natur.326..332C |s2cid=4351363 |doi-access=}}</ref> As mitochondria were known to be the result of the [[endosymbiosis]] of a [[proteobacterium]], it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in [[eukaryogenesis]]. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom [[Archezoa]]. This superkingdom was opposed to the [[Metakaryota]] superkingdom, grouping together the five other eukaryotic kingdoms ([[Animalia]], [[Protozoa]], [[Fungi]], [[Plantae]] and [[Chromista]]). This was known as the [[Archezoa hypothesis]], which has since been abandoned;<ref>{{cite journal|last=Poole |first=Anthony |author2=Penny, David |title=Engulfed by speculation |journal=[[Nature (journal)|Nature]] |date=21 June 2007 |volume=447 |issue=7147 |pages=913 |doi=10.1038/447913a |pmid=17581566 |s2cid=7753492 |url=http://www.cecm.usp.br/~cewinter/aulas/artigos/2007/eukarya_orig.pdf |access-date=15 March 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110706162409/http://www.cecm.usp.br/~cewinter/aulas/artigos/2007/eukarya_orig.pdf |archive-date=6 July 2011}}</ref> later schemes did not include the Archezoa–Metakaryota divide.<ref name="Cavalier-Smith 1998 203–66"/><ref name="Cavalier-Smith 2015"/> |
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! Kingdom (biology)|Kingdoms |
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|----- |
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{{clade |
|||
| bgcolor="lightgrey" rowspan="1" | '''[[Prokaryota]]''' |
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|label1= Life |
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| bgcolor="lavender" | '''[[Bacteria]]''' |
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|1={{clade |
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|----- |
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|1={{clade |
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| bgcolor="e0d0b0" rowspan="4" | '''[[Eukaryota]]''' |
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|label1=Superkingdom [[Prokaryote|Prokaryota]] |
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| bgcolor="pink" | '''[[Animalia]]''' |
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|1={{clade |
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| bgcolor="lightgreen" | '''[[Plantae]]''' |
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|1=Kingdom [[Eubacteria]] |
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| bgcolor="lightblue" | '''[[Fungi]]''' |
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|2=Kingdom [[Archaebacteria]] |
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| bgcolor="BurlyWood" | '''[[Chromista]]''' |
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}} |
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| bgcolor="khaki" | '''[[Protozoa]]''' |
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}} |
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|2={{clade |
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|label1=Superkingdom [[Archezoa]]‡ |
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|1={{clade |
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|1=Kingdom [[Archezoa]]‡ |
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}} |
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}} |
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|3={{clade |
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|label1=Superkingdom [[Metakaryota]]‡ |
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|1={{clade |
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|1=Kingdom [[Protozoa]] |
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|2=Kingdom [[Chromista]] |
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|3=Kingdom [[Plant]]ae |
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|4=Kingdom [[Fungus|Fungi]] |
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|5=Kingdom [[Animal]]ia |
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}} |
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}} |
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}} |
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}} |
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‡ No longer recognized by [[Taxonomy (biology)|taxonomists]]. |
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=== Six kingdoms (1998) === |
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In 1998, Cavalier-Smith published a six-kingdom model,<ref name="Cavalier-Smith 1998 203–66"/> which has been revised in subsequent papers. The version published in 2009 is shown below.<ref name="CavalierSmith2009">{{cite journal |last=Cavalier-Smith |first=Thomas |author-link=Thomas Cavalier-Smith |year=2009 |title=Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree |journal=Biology Letters |volume=6 |issue=3 |pages=342–345 |doi=10.1098/rsbl.2009.0948 |pmc=2880060 |pmid=20031978}}</ref><ref group=lower-alpha>Compared to the version Cavalier-Smith published in 2004, the [[Alveolata|alveolates]] and the [[rhizaria]]ns have been moved from Kingdom Protozoa to Kingdom Chromista.</ref><ref>{{cite journal |last=Cavalier-Smith |first=T. |year=2004 |title=Only six kingdoms of life |journal=[[Proceedings of the Royal Society of London B]] |volume=271 |pages=1251–1262 |url=http://www.cladocera.de/protozoa/cavalier-smith_2004_prs.pdf |access-date=2010-04-29 |doi=10.1098/rspb.2004.2705 |pmid=15306349 |issue=1545 |pmc=1691724 |df=dmy-all}}</ref> Cavalier-Smith no longer accepted the importance of the fundamental Eubacteria–Archaebacteria divide put forward by Woese and others and supported by recent research.<ref name="DagenEtAl2010"/> The kingdom [[Bacteria]] (sole kingdom of empire [[Prokaryota]]) was subdivided into two sub-kingdoms according to their membrane topologies: [[Unibacteria]] and [[Negibacteria]]. Unibacteria was divided into phyla [[Archaebacteria]] and [[Posibacteria]]; the bimembranous-unimembranous transition was thought to be far more fundamental than the long branch of genetic distance of Archaebacteria, viewed as having no particular biological significance. |
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Cavalier-Smith does not accept the requirement for taxa to be [[Monophyly|monophyletic]] ("holophyletic" in his terminology) to be valid. He defines Prokaryota, Bacteria, Negibacteria, Unibacteria, and Posibacteria as valid [[Paraphyly|paraphyla]] (therefore "monophyletic" in the sense he uses this term) taxa, marking important innovations of biological significance (in regard of the concept of biological [[Ecological niche|niche]]). |
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In the same way, his paraphyletic kingdom Protozoa includes the ancestors of Animalia, Fungi, Plantae, and Chromista. The advances of phylogenetic studies allowed Cavalier-Smith to realize that all the phyla thought to be [[archezoa]]ns (i.e. primitively amitochondriate eukaryotes) had in fact secondarily lost their mitochondria, typically by transforming them into new organelles: [[Hydrogenosome]]s. This means that all living eukaryotes are in fact [[metakaryote]]s, according to the significance of the term given by Cavalier-Smith. Some of the members of the defunct kingdom [[Archezoa]], like the phylum [[Microsporidia]], were reclassified into kingdom [[Fungi]]. Others were reclassified in kingdom [[Protozoa]], like [[Metamonada]] which is now part of infrakingdom [[Excavata]]. |
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Because Cavalier-Smith allows [[paraphyly]], the diagram below is an 'organization chart', not an 'ancestor chart', and does not represent an evolutionary tree. |
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{{clade |
|||
|label1= Life |
|||
|1={{clade |
|||
|1={{clade |
|||
|label1=Empire [[Prokaryote|Prokaryota]] |
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|1={{clade |
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|1=Kingdom [[Bacteria]] — includes [[Archaebacteria]] as part of a subkingdom |
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}} |
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}} |
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|2={{clade |
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|label1=Empire [[Eukaryote|Eukaryota]] |
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|1={{clade |
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|1=Kingdom [[Protozoa]] — e.g. [[Amoebozoa]], [[Choanozoa]], [[Excavata]] |
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|2=Kingdom [[Chromista]] — e.g. [[Alveolata]], [[Cryptomonad|cryptophytes]], [[Heterokonta]] ([[Brown Algae]], [[Diatoms]] etc.), [[Haptophyta]], [[Rhizaria]] |
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|3=Kingdom [[Plant]]ae — e.g. [[glaucophyte]]s, [[red alga|red]] and [[green alga]]e, [[land plants]] |
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|4=Kingdom [[Fungus|Fungi]] |
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|5=Kingdom [[Animal]]ia |
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}} |
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}} |
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}} |
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}} |
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{| role="presentation" class="wikitable mw-collapsible mw-collapsed" |
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|+ {{nowrap|Cavalier-Smith's six kingdom system (1998)<ref name="Cavalier-Smith 1998 203–66"/>}} |
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|-style="font-size: 80%;vertical-align: top;background: white" |
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|| |
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{{nowrap|'''Kingdom [[Bacteria]]'''{{br}} |
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Subkingdom [[Negibacteria]]{{br}} |
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Infrakingdom [[Lipobacteria]]{{br}} |
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Superphylum Eobacteria{{br}} |
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Phylum [[Heliobacteria]]{{br}} |
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Phylum [[Hadobacteria]]{{br}} |
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Subphylum [[Chlorobacteria]]{{br}} |
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Subphylum [[Deinobacteria]]{{br}} |
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Superphylum [[Endoflagellata]]{{br}} |
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Phylum [[Spirochaetae]]{{br}} |
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Subphylum [[Euspirochaetae]]{{br}} |
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Subphylum [[Leptospirae]]{{br}} |
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Infrakingdom [[Glycobacteria]]{{br}} |
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Superphylum [[Pimelobacteria]]{{br}} |
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Phylum [[Sphingobacteria]]{{br}} |
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Subphylum [[Chlorobibacteria]]{{br}} |
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Subphylum [[Flavobacteria]]{{br}} |
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Phylum [[Eurybacteria]]{{br}} |
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Subphylum [[Sclenobacteria]]{{br}} |
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Subphylum [[Fusobacteria]]{{br}} |
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Subphylum [[Fibrobacteria]]{{br}} |
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Phylum [[Cyanobacteria]]{{br}} |
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Subphylum [[Gloeobacteria]]{{br}} |
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Subphylum [[Phycobacteria]]{{br}} |
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Phylum [[Proteobacteria]]{{br}} |
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Subphylum [[Rhodobacteria]]{{br}} |
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Infraphylum [[Alphabacteria]]{{br}} |
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Infraphylum [[Chromatibacteria]]{{br}} |
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Subphylum [[Thiobacteria]]{{br}} |
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Superphylum [[Planctobacteria]]{{br}} |
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Phylum [[Planctobacteria]]{{br}} |
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Subkingdom [[Unibacteria]]{{br}} |
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Infrakingdom [[Posibacteria]]{{br}} |
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Phylum [[Posibacteria]]{{br}} |
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Subphylum [[Teichobacteria]]{{br}} |
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Infraphylum [[Endobacteria]]{{br}} |
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Infraphylum [[Actinobacteria]]{{br}} |
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Subphylum [[Togobacteria]]{{br}} |
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Infrakingdom [[Archaebacteria]]{{br}} |
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Phylum [[Mendosicutes]]{{br}} |
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Subphylum [[Euryarcheota]]{{br}} |
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Infraphylum [[Halomebacteria]]{{br}} |
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Infraphylum [[Eurytherma]]{{br}} |
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Subphylum [[Sulfobacteria]]{{br}}}} |
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|| |
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{{nowrap|'''Kingdom [[Protozoa]]'''{{br}} |
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'''Subkingdom [[Archezoa]]'''{{br}} |
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Phylum [[Metamonada]]{{br}} |
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Subphylum [[Eopharyngia]]{{br}} |
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Subphylum [[Axostylaria]]{{br}} |
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Phylum [[Trichozoa]]{{br}} |
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Subphylum [[Anaeromonada]]{{br}} |
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Subphylum [[Parabasala]]{{br}} |
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'''Subkingdom [[Neozoa]]'''{{br}} |
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'''Infrakingdom [[Sarcomastigota]]'''{{br}} |
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Phylum [[Neomonada]]{{br}} |
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Subphylum [[Apusozoa]]{{br}} |
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Subphylum [[Isomita]]{{br}} |
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Subphylum [[Choanozoa]]{{br}} |
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Phylum [[Cercozoa]]{{br}} |
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Subphylum [[Phytomyxa]]{{br}} |
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Subphylum [[Reticulofilosa]]{{br}} |
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Subphylum [[Monadofilosa]]{{br}} |
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Phylum [[Foraminifera]]{{br}} |
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Phylum [[Amoebozoa]]{{br}} |
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Subphylum [[Lobosa]]{{br}} |
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Subphylum [[Conosa]]{{br}} |
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Infraphylum [[Archamoebae]]{{br}} |
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Infraphylum [[Mycetozoa]]{{br}} |
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Superclass [[Eumyxa]]{{br}} |
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Superclass [[Dictyostelia]]{{br}} |
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'''Infrakingdom [[Discicristata]]'''{{br}} |
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Phylum [[Percolozoa]]{{br}} |
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Subphylum [[Tetramitia]]{{br}} |
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Subphylum [[Pseudociliata]]{{br}} |
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Phylum [[Euglenozoa]]{{br}} |
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Subphylum [[Plicostoma]]{{br}} |
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Subphylum [[Saccostoma]]{{br}} |
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'''Infrakingdom [[Alveolata]]'''{{br}} |
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Superphylum [[Miozoa]]{{br}} |
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Phylum [[Dinozoa]]{{br}} |
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Subphylum [[Protalveolata]]{{br}} |
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Subphylum [[Dinoflagellata]]{{br}} |
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Phylum [[Sporozoa]]{{br}} |
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Subphylum [[Gregarinae]]{{br}} |
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Subphylum [[Coccidiomorpha]]{{br}} |
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Subphylum [[Manubrispora]]{{br}} |
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Superphylum [[Heterokaryota]]{{br}} |
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Phylum [[Ciliophora]]{{br}} |
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Subphylum [[Tubulicorticata]]{{br}} |
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Subphylum [[Epiplasmata]]{{br}} |
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Subphylum [[Filocorticata]]{{br}} |
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'''Infrakingdom [[Actinopod|Actinopoda]]'''{{br}} |
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Phylum [[Heliozoa]]{{br}} |
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Phylum [[Radiozoa]]{{br}} |
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Subphylum [[Spasmaria]]{{br}} |
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Subphylum [[Radiolaria]]{{br}}}} |
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|| |
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{{nowrap|'''Kingdom [[Fungi]]'''{{br}} |
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'''Subkingdom [[Eomycota]]'''{{br}} |
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'''Phylum [[Archemycota]]'''{{br}} |
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Subphylum [[Dictyomycotina]]{{br}} |
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Class [[Chytridiomycetes]]{{br}} |
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Subclass [[Rumpomycetidae]]{{br}} |
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Subclass [[Spizomycetidae]]{{br}} |
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Class [[Enteromycetes]]{{br}} |
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Subphylum [[Melanomycotina]]{{br}} |
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Infraphylum [[Allomycotina]]{{br}} |
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Class [[Allomycetes]]{{br}} |
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Infraphylum [[Zygomycotina]]{{br}} |
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Superclass [[Eozygomycetia]]{{br}} |
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Class [[Bolomycetes]]{{br}} |
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Class [[Glomomycetes]]{{br}} |
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Superclass [[Neozygomycetia]]{{br}} |
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Class [[Zygomycetes]]{{br}} |
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Subclass [[Mucoromycetidae]]{{br}} |
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Subclass [[Meromycetidae]]{{br}} |
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Class [[Zoomycetes]]{{br}} |
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Subclass [[Entomycetidae]]{{br}} |
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Subclass [[Pedomycetidae]]{{br}} |
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Superorder [[Trichomycetalia]]{{br}} |
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Superorder [[Pyxomycetalia]]{{br}} |
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'''Phylum [[Microsporidia]]'''{{br}} |
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Class [[Minisporea]]{{br}} |
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Class [[Microsporea]]{{br}} |
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Subclass [[Pleistophorea]]{{br}} |
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Subclas [[Disporea]]{{br}} |
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'''Subkingdom [[Neomycota]]'''{{br}} |
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'''Phylum [[Ascomycota]]'''{{br}} |
|||
Subphylum [[Hemiascomycotina]]{{br}} |
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Class [[Taphrinomycetes]]{{br}} |
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Class [[Geomycetes]]{{br}} |
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Class [[Endomycetes]]{{br}} |
|||
Subclass [[Dipomycetidae]]{{br}} |
|||
Subclass [[Saccharomycetidae]]{{br}} |
|||
Subphylum [[Euascomycotina]]{{br}} |
|||
Class [[Discomycetes]]{{br}} |
|||
Subclass [[Calycomycetidae]]{{br}} |
|||
Subclass [[Lecomycetidae]]{{br}} |
|||
Subclass [[Pezomycetidae]]{{br}} |
|||
Class [[Pyrenomycetes]]{{br}} |
|||
Subclass [[Verrucomycetidae]]{{br}} |
|||
Subclass [[Ostiomycetidae]]{{br}} |
|||
Class [[Loculomycetes]]{{br}} |
|||
Subclass [[Dendromycetidae]]{{br}} |
|||
Subclass [[Loculoascomycetidae]]{{br}} |
|||
Class [[Plectomycetes]]{{br}} |
|||
'''Phylum [[Basidiomycota]]'''{{br}} |
|||
Subphylum [[Septomycotina]]{{br}} |
|||
Class [[Septomycetes]]{{br}} |
|||
Subclass [[Sporidiomycetidae]]{{br}} |
|||
Subclass [[Uredomycetidae]]{{br}} |
|||
Subphylum [[Orthomycotina]]{{br}} |
|||
Superclass [[Hemibasidiomycetia]]{{br}} |
|||
Class [[Ustomycetes]]{{br}} |
|||
Superclass [[Hymenomycetia]]{{br}} |
|||
Class [[Gelimycetes]]{{br}} |
|||
Subclass [[Tremellomycetidae]]{{br}} |
|||
Subclass [[Dacrymycetidae]]{{br}} |
|||
Subclass [[Auromycetidae]]{{br}} |
|||
Class [[Homobasidiomycetes]]{{br}} |
|||
Subclass [[Clavomycetidae]]{{br}} |
|||
Subclass [[Pileomycetidae]] |
|||
}} |
|||
|| |
|||
{{nowrap|'''Kingdom [[Animalia]]'''{{br}} |
|||
'''Subkingdom [[Radiata]]'''{{br}} |
|||
'''Infrakingdom [[Spongiaria]]'''{{br}} |
|||
Phylum [[Porifera]]{{br}} |
|||
Subphylum [[Hyalospongiae]]{{br}} |
|||
Subphylum [[Calcispongiae]]{{br}} |
|||
Subphylum [[Archaeocyatha]] {{extinct}}{{br}} |
|||
'''Infrakingdom [[Coelenterata]]'''{{br}} |
|||
Phylum [[Cnidaria]]{{br}} |
|||
Subphylum [[Anthozoa]]{{br}} |
|||
Subphylum [[Medusozoa]]{{br}} |
|||
'''Infrakingdom [[Placozoa]]'''{{br}} |
|||
Phylum [[Placozoa]]{{br}} |
|||
'''Subkingdom [[Myxozoa]]'''{{br}} |
|||
Phylum [[Myxosporidia]]{{br}} |
|||
'''Subkingdom [[Bilateria]]'''{{br}} |
|||
'''Branch [[Protostomia]]'''{{br}} |
|||
'''Infrakingdom [[Lophozoa]]'''{{br}} |
|||
Superphylum [[Polyzoa]]{{br}} |
|||
Phylum [[Bryozoa]]{{br}} |
|||
Subphylum [[Gymnolaemata]]{{br}} |
|||
Subphylum [[Lophopoda]]{{br}} |
|||
Phylum [[Kamptozoa]]{{br}} |
|||
Subphylum [[Entoprocta]]{{br}} |
|||
Subphylum [[Cycliophora]]{{br}} |
|||
Superphylum [[Conchozoa]]{{br}} |
|||
Phylum [[Mollusca]]{{br}} |
|||
Subphylum [[Bivalvia]]{{br}} |
|||
Subphylum [[Glossophora]]{{br}} |
|||
Infraphylum [[Univalvia]]{{br}} |
|||
Infraphylum [[Spiculata]]{{br}} |
|||
Infraphylum [[Cephalopoda]]{{br}} |
|||
Phylum [[Brachiozoa]]{{br}} |
|||
Subphylum [[Brachiopoda]]{{br}} |
|||
Subphylum [[Phoronida]]{{br}} |
|||
Superphylum [[Sipuncula]]{{br}} |
|||
Phylum [[Sipuncula]]{{br}} |
|||
Superphylum [[Vermizoa]]{{br}} |
|||
Phylum [[Annelida]]{{br}} |
|||
Subphylum [[Polychaeta]]{{br}} |
|||
Infraphylum [[Operculata]]{{br}} |
|||
Infraphylum [[Pharyngata]]{{br}} |
|||
Subphylum [[Clitellata]]{{br}} |
|||
Subphylum [[Echiura]]{{br}} |
|||
Subphylum [[Pogonophora (worm)|Pogonophora]]{{br}} |
|||
Phylum [[Nemertina]]{{br}} |
|||
'''Infrakingdom [[Chaetognathi]]'''{{br}} |
|||
Phylum [[Chaetognatha]]{{br}} |
|||
'''Infrakingdom [[Ecdysozoa]]'''{{br}} |
|||
Superphylum [[Haemopoda]]{{br}} |
|||
Phylum [[Arthropoda]]{{br}} |
|||
Subphylum [[Cheliceromorpha]]{{br}} |
|||
Infraphylum [[Pycnogonida]]{{br}} |
|||
Infraphylum [[Chelicerata]]{{br}} |
|||
Subphylum [[Trilobitomorpha]] {{extinct}}{{br}} |
|||
Subphylum [[Mandibulata]]{{br}} |
|||
Infraphylum [[Crustacea]]{{br}} |
|||
Infraphylum [[Myriapoda]]{{br}} |
|||
Infraphylum [[Insecta]]{{br}} |
|||
Phylum [[Lobopoda]]{{br}} |
|||
Subphylum [[Onychophora]]{{br}} |
|||
Subphylum [[Tardigrada]]{{br}} |
|||
Superphylum [[Nemathelminthes]]{{br}} |
|||
Phylum [[Nemathelminthes]]{{br}} |
|||
Subphylum [[Scalidorhyncha]]{{br}} |
|||
Infraphylum [[Priapozoa]]{{br}} |
|||
Infraphylum [[Kinorhyncha]]{{br}} |
|||
Subphylum [[Nematoida]]{{br}} |
|||
Infraphylum [[Nematoda]]{{br}} |
|||
Infraphylum [[Nematomorpha]]{{br}} |
|||
'''Infrakingdom [[Platyzoa]]'''{{br}} |
|||
Phylum [[Acanthognatha]]{{br}} |
|||
Subphylum [[Trochata]]{{br}} |
|||
Infraphylum [[Rotifera]]{{br}} |
|||
Infraphylum [[Acanthocephala]]{{br}} |
|||
Subphylum [[Monokonta]]{{br}} |
|||
Phylum [[Platyhelminthes]]{{br}} |
|||
Subphylum [[Turbellaria]]{{br}} |
|||
Infraphylum [[Mucorhabda]]{{br}} |
|||
Infraphylum [[Rhabditophora]]{{br}} |
|||
Subphylum [[Neodermata]]{{br}} |
|||
Infraphylum [[Trematoda]]{{br}} |
|||
Infraphylum [[Cercomeromorpha]]{{br}} |
|||
'''Branch [[Deuterostomia]]'''{{br}} |
|||
'''Infrakingdom [[Coelomopora]]'''{{br}} |
|||
Phylum [[Hemichordata]]{{br}} |
|||
Subphylum [[Pterobranchia]]{{br}} |
|||
Subphylum [[Enteropneusta]]{{br}} |
|||
Phylum [[Echinodermata]]{{br}} |
|||
Subphylum [[Homalozoa]]{{br}} |
|||
Subphylum [[Pelmatozoa]]{{br}} |
|||
Infraphylum [[Blastozoa]]{{br}} |
|||
Infraphylum [[Crinozoa]]{{br}} |
|||
Subphylum [[Eleutherozoa]]{{br}} |
|||
Infraphylum [[Asterozoa]]{{br}} |
|||
Infraphylum [[Echinozoa]]{{br}} |
|||
'''Infrakingdom [[Chordonia]]'''{{br}} |
|||
Phylum [[Urochorda]]{{br}} |
|||
Subphylum [[Tunicata]]{{br}} |
|||
Infraphylum [[Ascidiae]]{{br}} |
|||
Infraphylum [[Thaliae]]{{br}} |
|||
Subphylum [[Larvacea|Appendicularia]]{{br}} |
|||
Phylum [[Chordata]]{{br}} |
|||
Subphylum [[Acraniata]]{{br}} |
|||
Infraphylum [[Cephalochordata]]{{br}} |
|||
Infraphylum [[Conodonta]] {{extinct}}{{br}} |
|||
Subphylum [[Vertebrata]]{{br}} |
|||
Infraphylum [[Agnatha]]{{br}} |
|||
Infraphylum [[Gnathostomata]]{{br}} |
|||
'''Subkingdom [[Mesozoa]]'''{{br}} |
|||
Phylum [[Mesozoa]] |
|||
}} |
|||
|| |
|||
{{nowrap|'''Kingdom [[Plantae]]'''{{br}} |
|||
'''Subkingdom [[Biliphyta]]'''{{br}} |
|||
'''Infrakingdom [[Glaucophyta]]'''{{br}} |
|||
Phylum [[Glaucophyta]]{{br}} |
|||
'''Infrakingdom [[Rhodophyta]]'''{{br}} |
|||
Phylum [[Rhodophyta]]{{br}} |
|||
Subphylum [[Rhodellophytina]]{{br}} |
|||
Subphylum [[Macrorhodophytina]]{{br}} |
|||
'''Subkingdom [[Viridiplantae]]'''{{br}} |
|||
'''Infrakingdom [[Chlorophyta]]'''{{br}} |
|||
Phylum [[Chlorophyta]]{{br}} |
|||
Subphylum [[Chlorophytina]]{{br}} |
|||
Infraphylum [[Prasinophytae]]{{br}} |
|||
Infraphylum [[Tetraphytae]]{{br}} |
|||
Subphylum [[Phragmophytina]]{{br}} |
|||
Infraphylum [[Charophytae]]{{br}} |
|||
Infraphylum [[Rudophytae]]{{br}} |
|||
'''Infrakingdom [[Cormophyta]]'''{{br}} |
|||
Phylum [[Moss|Bryophyta]]{{br}} |
|||
Subphylum [[Hepaticae]]{{br}} |
|||
Subphylum [[Anthocerotae]]{{br}} |
|||
Subphylum [[Musci]]{{br}} |
|||
Infraphylum [[Sphagneae]]{{br}} |
|||
Infraphylum [[Bryatae]]{{br}} |
|||
Phylum [[Tracheophyta]]{{br}} |
|||
Subphylum [[Pteridophytina]]{{br}} |
|||
Infraphylum [[Psilophytae]]{{br}} |
|||
Infraphylum [[Lycophytae]]{{br}} |
|||
Infraphylum [[Sphenophytae]]{{br}} |
|||
Infraphylum [[Filices]]{{br}} |
|||
Subphylum [[Spermatophytina]]{{br}} |
|||
Infraphylum [[Gymnospermae]]{{br}} |
|||
Infraphylum [[Angiospermae]] |
|||
}} |
|||
|| |
|||
{{nowrap|'''Kingdom [[Chromista]]'''{{br}} |
|||
'''Subkingdom [[Cryptista]]'''{{br}} |
|||
Phylum [[Cryptophyta]]{{br}} |
|||
'''Subkingdom [[Chromobiota]]'''{{br}} |
|||
'''Infrakingdom [[Heterokonta]]'''{{br}} |
|||
Superphylum [[Sagenista]]{{br}} |
|||
Phylum [[Sagenista]]{{br}} |
|||
Subphylum [[Bicoecia]]{{br}} |
|||
Subphylum [[Labyrinthista]]{{br}} |
|||
Phylum [[Ochrophyta]]{{br}} |
|||
Subphylum [[Phaeista]]{{br}} |
|||
Infraphylum [[Hypogyrista]]{{br}} |
|||
Infraphylum [[Chrysista]]{{br}} |
|||
Subphylum [[Diatomeae]]{{br}} |
|||
Phylum [[Bigyra]]{{br}} |
|||
Subphylum [[Bigyromonada]]{{br}} |
|||
Subphylum [[Pseudofungi]]{{br}} |
|||
Subphylum [[Opalinata]]{{br}} |
|||
'''Infrakingdom [[Haptophyta]]'''{{br}} |
|||
Phylum [[Haptophyta]] |
|||
}} |
|||
|} |
|} |
||
== |
=== Seven kingdoms === |
||
Cavalier-Smith and his collaborators revised their classification in 2015. In this scheme they introduced two superkingdoms of Prokaryota and Eukaryota and seven kingdoms. Prokaryota have two kingdoms: [[Bacteria]] and [[Archaea]]. (This was based on the consensus in the [[Bacterial taxonomy|Taxonomic Outline of Bacteria and Archaea]], and the [[Catalogue of Life]]). The Eukaryota have five kingdoms: Protozoa, Chromista, Plantae, Fungi, and Animalia. In this classification a [[protist]] is any of the eukaryotic [[unicellular organism]]s.<ref name="Cavalier-Smith 2015">{{cite journal |last1=Ruggiero |first1=Michael A. |last2=Gordon |first2=Dennis P. |last3=Orrell |first3=Thomas M. |last4=Bailly |first4=Nicolas |last5=Bourgoin |first5=Thierry |last6=Brusca |first6=Richard C. |last7=Cavalier-Smith |first7=Thomas |last8=Guiry |first8=Michael D. |last9=Kirk |first9=Paul M. |last10=Thuesen |first10=Erik V. |title=A higher level classification of all living organisms |journal=[[PLOS ONE]] |date=2015 |volume=10 |issue=4 |pages=e0119248 |doi=10.1371/journal.pone.0119248 |pmid=25923521 |pmc=4418965 |bibcode=2015PLoSO..1019248R |doi-access=free}}</ref> |
|||
{{clade |
|||
|label1= Life |
|||
|1={{clade |
|||
|1={{clade |
|||
|label1=Superkingdom [[Prokaryote|Prokaryota]] |
|||
|1={{clade |
|||
|1=Kingdom [[Bacteria]] |
|||
|2=Kingdom [[Archaea]] |
|||
}} |
|||
}} |
|||
|2={{clade |
|||
|label1=Superkingdom [[Eukaryote|Eukaryota]] |
|||
|1={{clade |
|||
|1=Kingdom [[Protozoa]] — e.g. [[Amoebozoa]], [[Choanozoa]], [[Excavata]] |
|||
|2=Kingdom [[Chromista]] — e.g. [[Alveolata]], [[Cryptomonad|cryptophytes]], [[Heterokonta]] ([[Brown Algae]], [[Diatoms]] etc.), [[Haptophyta]], [[Rhizaria]] |
|||
|3=Kingdom [[Plant]]ae — e.g. [[glaucophyte]]s, [[red alga|red]] and [[green alga]]e, [[land plants]] |
|||
|4=Kingdom [[Fungus|Fungi]] |
|||
|5=Kingdom [[Animal]]ia |
|||
}} |
|||
}} |
|||
}} |
|||
}} |
|||
=== Summary === |
|||
{{Full biological kingdom classification}} |
|||
The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach: |
|||
* Kingdoms such as Protozoa represent [[evolutionary grade|grade]]s rather than [[clade]]s, and so are rejected by [[cladistics|phylogenetic classification]] systems. |
|||
* The most recent research does not support the classification of the eukaryotes into any of the standard systems. {{As of|2010|April}}, no set of kingdoms is sufficiently supported by research to attain widespread acceptance. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."<ref>{{cite journal |last1=Roger |first1=A.J. |last2=Simpson |first2=A.G.B. |year=2009 |title=Evolution: Revisiting the Root of the Eukaryote Tree |journal=[[Current Biology]] |volume=19 |issue=4 |pages=R165–7 |doi=10.1016/j.cub.2008.12.032 |pmid=19243692 |s2cid=13172971 |name-list-style=amp |doi-access=free}}</ref> |
|||
== Beyond traditional kingdoms == |
|||
{{anchor|Modern view}} |
|||
While the concept of kingdoms continues to be used by some taxonomists, there has been a movement away from traditional kingdoms, as they are no longer seen as providing a [[Cladistics|cladistic]] classification, where there is emphasis in arranging organisms into [[Clade|natural groups]].<ref name="SimpsonRoger2004"/> |
|||
=== Three domains of life === |
|||
{{main|Three-domain system|Domain (biology)}} |
|||
{{PhylomapB||caption=A [[phylogenetic tree]] based on [[rRNA]] data showing Woese's [[three-domain system]]. All smaller branches can be considered kingdoms.|size = 440px}} |
|||
Based on RNA studies, [[Carl Woese]] thought life could be divided into three large divisions and referred to them as the "three primary kingdom" model or "urkingdom" model.<ref name="Balch_Magrum_Fox_Wolfe_Woese">{{cite journal |last1=Balch |first1=W.E. |last2=Magrum |first2=L.J. |last3=Fox |first3=G.E. |last4=Wolfe |first4=C.R. |last5=Woese |first5=C.R. |name-list-style=amp |date=August 1977 |title=An ancient divergence among the bacteria |journal=[[Journal of Molecular Evolution]] |volume=9 |issue=4 |pages=305–311 |doi=10.1007/BF01796092 |pmid=408502 |bibcode=1977JMolE...9..305B |s2cid=27788891}}</ref> |
|||
In 1990, the name "domain" was proposed for the highest rank.<ref name="Woese"/> This term represents a synonym for the category of dominion (lat. dominium), introduced by Moore in 1974.<ref name=Moore1974>{{cite journal |last=Moore |first=R.T. |year=1974 |title=Proposal for the recognition of super ranks |journal=Taxon |volume=23 |issue=4 |pages=650–652 |doi=10.2307/1218807 |jstor=1218807 |url=http://www.iapt-taxon.org/historic/Congress/IBC_1975/Prop034bis-037.pdf}}</ref> Unlike Moore, Woese et al. (1990) did not suggest a Latin term for this category, which represents a further argument supporting the accurately introduced term dominion.<ref name=Luketa2012>{{cite journal |last=Luketa |first=S. |year=2012 |title = New views on the megaclassification of life |journal=[[Protistology]] |volume=7 |issue=4 |pages=218–237 |url=http://protistology.ifmo.ru/num7_4/luketa_protistology_7-4.pdf}}</ref> |
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Woese divided the prokaryotes (previously classified as the Kingdom Monera) into two groups, called [[bacteria|Eubacteria]] and [[Archaea|Archaebacteria]], stressing that there was as much genetic difference between these two groups as between either of them and all eukaryotes. |
|||
{{clade |
|||
|label1= [[Life]] |
|||
|1={{clade |
|||
|1=Domain [[Bacteria]] ([[Eubacteria]]) |
|||
|2=Domain [[Archaea]] ([[Archaebacteria]]) |
|||
|3=Domain [[Eukaryote|Eukarya]] ([[Eukaryota]]) |
|||
}} |
|||
}} |
|||
According to genetic data, although eukaryote groups such as plants, fungi, and animals may look different, they are more closely related to each other than they are to either the Eubacteria or Archaea. It was also found that the eukaryotes are more closely related to the Archaea than they are to the Eubacteria. Although the primacy of the Eubacteria-Archaea divide has been questioned, it has been upheld by subsequent research.<ref name="DagenEtAl2010">{{cite journal |last1=Dagan |first1=T. |last2=Roettger |first2=M. |last3=Bryant |last4=Martin |first4=W. |year=2010 |title=Genome Networks Root the Tree of Life between Prokaryotic Domains |journal=[[Genome Biology and Evolution]] |volume=2 |pages=379–92 |doi=10.1093/gbe/evq025 |pmid=20624742 |pmc=2997548 |name-list-style=amp }}</ref> There is no consensus on how many kingdoms exist in the classification scheme proposed by Woese. |
|||
=== Eukaryotic supergroups === |
|||
{{anchor|Kingdoms of the Eukaryota}} |
|||
{{Main|Supergroup (biology)}} |
|||
In 2004, a review article by Simpson and Roger noted that the Protista were "a [[Wastebasket taxon|grab-bag]] for all [[eukaryote]]s that are not animals, plants or fungi". They held that only monophyletic groups should be accepted as formal ranks in a classification and that – while this approach had been impractical previously (necessitating "literally dozens of eukaryotic 'kingdoms{{'"}}) – it had now become possible to divide the eukaryotes into "just a few major groups that are probably all monophyletic".<ref name="SimpsonRoger2004">{{cite journal |title=The real 'kingdoms' of eukaryotes |last1=Simpson |first1=Alastair G.B. |last2=Roger |first2=Andrew J. |journal=[[Current Biology]] |volume=14 |issue=17 |pages=R693–R696 |doi=10.1016/j.cub.2004.08.038 |pmid=15341755|year=2004 |s2cid=207051421 |doi-access=free}}</ref> |
|||
On this basis, the diagram opposite (redrawn from their article) showed the real "kingdoms" (their quotation marks) of the eukaryotes.<ref name="SimpsonRoger2004" /> A classification which followed this approach was produced in 2005 for the International Society of Protistologists, by a committee which "worked in collaboration with specialists from many societies". It divided the eukaryotes into the same six "supergroups".<ref name=Adl2005>{{cite journal |vauthors=Adl SM, ((Simpson AGB)), Farmer MA, Andersen RA, Anderson OR, Barta JR, Bowser SS, Brugerolle G, Fensome RA, Fredericq S, James TY, Karpov S, Kugrens P, Krug J, Lane CE, Lewis LA, Lodge J, Lynn DH, Mann DG, Mccourt RM, Mendoza L, Moestrup Ø, Mozley-Standridge SE, Nerad TA, Shearer CA, Smirnov AV, Spiegel FW, Taylor MF |display-authors=6 |title=The new higher-level classification of eukaryotes with emphasis on the taxonomy of protists |journal=[[Journal of Eukaryotic Microbiology]] |year=2005 |volume=52 |issue=5 |pages=399–451 |doi=10.1111/j.1550-7408.2005.00053.x |pmid=16248873 |s2cid=8060916 |doi-access=free|url=http://doc.rero.ch/record/14409/files/PAL_E1847.pdf }}</ref> The published classification deliberately did not use formal taxonomic ranks, including that of "kingdom". |
|||
{{clade |
|||
|label1= [[Life]] |
|||
|1={{clade |
|||
|1={{clade |
|||
|label1=Domain [[Bacteria]] |
|||
|1={{clade |1= [[prokaryotic]] [[Bacteria]] }} |
|||
}} |
|||
|2={{clade |
|||
|label1=Domain [[Archaea]] |
|||
|1={{clade |1= [[prokaryotic]] [[Archaea]]ns }} |
|||
}} |
|||
|3={{clade |
|||
|label1=Domain [[Eukaryota]] |
|||
|1={{clade |
|||
|label1= [[Excavata]] |
|||
|1= various [[flagellate]] protozoa |
|||
|label2= [[Amoebozoa]] |
|||
|2= most lobose [[amoeboid]]s and [[slime mould]]s |
|||
|label3= [[Opisthokonta]] |
|||
|3= [[animal]]s, [[fungus|fungi]], [[choanoflagellate]]s, etc. |
|||
|label4= [[Rhizaria]] |
|||
|4= [[Foraminifera]], [[Radiolaria]], and various other [[amoeboid]] protozoa |
|||
|label5= [[Chromalveolate|Chromalveolata]] |
|||
|5= [[Heterokont|Stramenopiles]] ([[Brown Algae]], [[Diatoms]], [[Ochrophyte|etc.]]), [[haptophyte|Haptophyta]], [[cryptomonad|Cryptophyta]] (or cryptomonads), and [[alveolate|Alveolata]] |
|||
|label6= [[Archaeplastida]] (or [[Primoplantae]]) |
|||
|6= [[Embryophyte|Land plants]], [[green alga]]e, [[red alga]]e, and [[glaucophyte]]s |
|||
}} |
|||
}} |
|||
}} |
|||
}} |
|||
In this system the multicellular animals ([[Metazoa]]) are descended from the same ancestor as both the unicellular [[choanoflagellate]]s and the fungi which form the [[Opisthokonta]].<ref name=Adl2005/> Plants are thought to be more distantly related to animals and fungi. |
|||
[[File:Eukaryote Phylogeny.png|alt=Eukaryotic tree of life showing the diversity of eukaryotic cells.|thumb|400px|One hypothesis of eukaryotic relationships depicted by Alastair Simpson]] |
|||
However, in the same year as the International Society of Protistologists' classification was published (2005), doubts were being expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata,<ref>{{cite journal |last1=Harper |first1=J. T. |last2=Waanders |first2=E. |last3=Keeling |first3=P. J. |year=2005 |title=On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes |journal=[[International Journal of Systematic and Evolutionary Microbiology]] |volume=55 |issue=Pt 1 |pmid=15653923 |pages=487–496 |name-list-style=amp |doi=10.1099/ijs.0.63216-0 |df=dmy-all |doi-access=free}}</ref> and a review in 2006 noted the lack of evidence for several of the six proposed supergroups.<ref name="parfrey">{{cite journal |last1=Parfrey |first1=Laura W. |last2=Barbero |first2=Erika |last3=Lasser |first3=Elyse |last4=Dunthorn |first4=Micah |year=2006 |last5=Bhattacharya |first5=Debashish |last6=Patterson |first6=David J. |last7=Katz |first7=Laura A. |name-list-style=amp |title=Evaluating support for the current classification of eukaryotic diversity |journal=[[PLOS Genetics]] |volume=2 |issue=12 |pages=e220 |doi=10.1371/journal.pgen.0020220 |pmid=17194223 |pmc=1713255 |doi-access=free }}</ref> |
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{{As of|2010}}, there is widespread agreement that the Rhizaria belong with the Stramenopiles and the Alveolata, in a [[clade]] dubbed the [[SAR supergroup]],<ref name="Burki2007p4">{{Harvnb|Burki|Shalchian-Tabrizi|Minge|Skjæveland |2007|p=4}}</ref> so that Rhizaria is not one of the main eukaryote groups.<ref name="CavalierSmith2009"/><ref name="Burki2007"/><ref name="Burki2008">{{cite journal |last1=Burki |first1=Fabien |last2=Shalchian-Tabrizi |first2=Kamran |last3=Pawlowski |first3=Jan |year=2008 |title=Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes |journal=[[Biology Letters]] |pmid=18522922 |volume=4 |issue=4 |pmc=2610160 |pages=366–369 |doi=10.1098/rsbl.2008.0224 |name-list-style=amp}}</ref><ref name="Burki2009">{{cite journal |last1=Burki |first1=F. |last2=Inagaki |year=2009 |first2=Y. |last3=Brate |first3=J. |last4=Archibald |first4=J. M. |last5=Keeling |first5=P. J. |last6=Cavalier-Smith |first6=T. |last7=Sakaguchi |first7=M. |last8=Hashimoto |first8=T. |last9=Horak |first9=A. |last10=Kumar |first10=S. |last11=Klaveness |first11=D.|author-link11=Dag Klaveness (limnologist) |last12=Jakobsen |first12=K. S. |last13=Pawlowski |first13=J. |last14=Shalchian-Tabrizi |first14=K. |title=Large-scale phylogenomic analyses reveal that two enigmatic protist lineages, Telonemia and Centroheliozoa, are related to photosynthetic Chromalveolates |journal=[[Genome Biology and Evolution]] |volume=1 |pages=231–238 |doi=10.1093/gbe/evp022 |pmc=2817417 |pmid=20333193 |display-authors=8}}</ref><ref name="Hackett2007">{{cite journal |last1=Hackett |first1=J.D. |last2=Yoon |first2=H.S. |last3=Li |first3=S. |last4=Reyes-Prieto |first4=A.|last5=Rummele |first5=S.E. |last6=Bhattacharya |first6=D. |name-list-style=amp |year=2007 |title=Phylogenomic analysis supports the monophyly of cryptophytes and haptophytes and the association of Rhizaria with chromalveolates |journal=[[Molecular Biology and Evolution]] |volume=24 |issue=8 |pages=1702–1713 |doi=10.1093/molbev/msm089 |pmid=17488740 |doi-access=free}}</ref> Beyond this, there does not appear to be a consensus. Rogozin ''et al.'' in 2009 noted that "The deep phylogeny of eukaryotes is an extremely difficult and controversial problem."<ref>{{cite journal |last1=Rogozin |first1=I.B. |last2=Basu |first2=M.K. |last3=Csürös |first3=M.|last4=Koonin |first4=E.V. |year=2009 |title=Analysis of rare genomic changes does not support the unikont–bikont phylogeny, and suggests cyanobacterial symbiosis as the point of primary radiation of eukaryotes |journal=[[Genome Biology and Evolution]] |volume=1 |pages=99–113 |doi=10.1093/gbe/evp011 |pmc=2817406 |name-list-style=amp |pmid=20333181}}</ref> {{As of|2010|December}}, there appears to be a consensus that the six supergroup model proposed in 2005 does not reflect the true phylogeny of the eukaryotes and hence how they should be classified, although there is no agreement as to the model which should replace it.<ref name="Burki2007">{{cite journal |last1=Burki |first1=Fabien |last2=Shalchian-Tabrizi |first2=Kamran |last3=Minge |first3=Marianne |last4=Skjæveland |first4=Åsmund |last5=Nikolaev |first5=Sergey I. |last6=Jakobsen |first6=Kjetill S. |last7=Pawlowski |first7=Jan |name-list-style=amp |editor1-last=Butler |year=2007 |editor1-first=Geraldine |title=Phylogenomics reshuffles the eukaryotic supergroups |journal=[[PLOS ONE]] |volume=2 |issue=8 |pages=e790 |doi=10.1371/journal.pone.0000790 |pmid=17726520 |pmc=1949142 |bibcode=2007PLoSO...2..790B |doi-access=free}}</ref><ref name=Burki2008/><ref name=KimGraham2008>{{cite journal |last1=Kim |first1=E. |last2=Graham |first2=L. E. |year=2008 |title=EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata |journal=[[PLOS ONE]] |volume=3 |issue=7 |pages=e2621 |editor1-last=Redfield |editor1-first=Rosemary Jeanne |doi=10.1371/journal.pone.0002621 |pmid=18612431 |pmc=2440802 |name-list-style=amp |last3=Redfield |first3=Rosemary Jeanne |bibcode=2008PLoSO...3.2621K |author3-link=Rosemary Redfield |doi-access=free}}</ref>{{clear}} |
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=== Comparison of top level classification === |
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{{further|Tree of life (biology)#Developments since 1990}} |
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Some authors have added [[non-cellular life]] to their classifications. This can create a "superdomain" called "Acytota", also called "Aphanobionta", of non-cellular life; with the other superdomain being "[[cytota]]" or cellular life.<ref name="pmidhttps://pubmed.ncbi.nlm.nih.gov/26305806/">{{cite journal |author=Trifonov EN, Kejnovsky E |title=Acytota - associated kingdom of neglected life. |journal=J Biomol Struct Dyn |year=2016 |volume= 34 |issue= 8 |pages=1641–8 |pmid=26305806 |doi=10.1080/07391102.2015.1086959 |pmc= |s2cid=38178747 |url=https://pubmed.ncbi.nlm.nih.gov/26305806/}}</ref><ref name="Biological systematics : the state of the art p. ">{{cite book |title=Biological systematics: The state of the art |publication-place=London |isbn=0-412-36440-9 |oclc=27895507 |page= |last1=Minelli |first1=Alessandro |year=1993}}</ref> The [[eocyte hypothesis]] proposes that the [[eukaryote]]s emerged from a phylum within the [[archaea]] called the [[Thermoproteota]] (formerly known as eocytes or Crenarchaeota).<ref name=Archibald>{{cite journal |first1=John M. |last1=Archibald |title=The eocyte hypothesis and the origin of eukaryotic cells |journal=[[PNAS]] |volume=105 |issue=51 |pages=20049–20050 |date=23 December 2008 |doi=10.1073/pnas.0811118106|pmid=19091952 |bibcode=2008PNAS..10520049A |pmc=2629348 |doi-access=free }}</ref><ref name=Lake>{{cite journal |first1=James A. |last1= Lake |first2=Eric |last2=Henderson |first3=Melanie |last3=Oakes |first4=Michael W. |last4=Clark |title=Eocytes: A new ribosome structure indicates a kingdom with a close relationship to eukaryotes |journal=[[PNAS]] |volume=81 |pages=3786–3790 |date=June 1984 |issue=12 |doi=10.1073/pnas.81.12.3786 |pmid=6587394 |pmc=345305 |bibcode=1984PNAS...81.3786L |doi-access=free}}</ref> |
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{{biological classification with acellular}} |
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== Viruses == |
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The [[International Committee on Taxonomy of Viruses]] uses the taxonomic rank "kingdom" in the classification of viruses (with the suffix ''-virae''); but this is beneath the top level classifications of [[Realm (virology)|realm]] and subrealm.<ref name=ictvcode >{{cite web |url=https://ictv.global/about/code |title=ICTV Code |website=talk.ictvonline.org |publisher=International Committee on Taxonomy of Viruses |access-date=26 April 2020}}</ref> |
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There is ongoing debate as to whether [[viruses]] can be included in the tree of life. The <!-- since no number of "in favor" given, why say 'ten' -->arguments against include the fact that they are obligate intracellular [[parasites]] that lack [[metabolism]] and are not capable of [[Self-replication|replication]] outside of a host cell.<ref name="Moreira and López-García">{{cite journal |last=Moreira |first=David |author2=Purificación López-García |title=Ten reasons to exclude viruses from the tree of life |journal=[[Nature Reviews Microbiology]] |year=2009 |volume=7 |pages=306–311 |issue=4 |doi=10.1038/nrmicro2108 |pmid=19270719 |s2cid=3907750}}</ref><ref name="Luketa 2012">{{cite journal |title=New views on the megaclassification of life |journal=[[Protistology]] |date=2012 |first=Stefan |last=Luketa |volume=7 |issue=4 |pages=218–237 |url=http://protistology.ifmo.ru/num7_4/luketa_protistology_7-4.pdf}}</ref> Another argument is that their placement in the tree would be problematic, since it is suspected that viruses have various evolutionary origins,<ref name="Moreira and López-García" /> and they have a penchant for harvesting [[nucleotide sequences]] from their hosts. |
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On the other hand, there are arguments in favor of their inclusion.<ref name="Nagendra et al. 2009">{{cite journal |last1=Hegde |first1=Nagendra |first2=Mohan S. |last2=Maddur |first3=Srini V. |last3=Kaveri |first4=Jagadeesh |last4=Bayry |name-list-style=amp |title=Reasons to include viruses in the tree of life |journal=[[Nature Reviews Microbiology]] |year=2009 |volume=7 |pages=615 |issue=8 |doi=10.1038/nrmicro2108-c1 |pmid=19561628 |doi-access=free}}</ref> |
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One of these comes from the discovery of unusually large and complex viruses, such as [[Mimivirus]], that possess typical cellular genes.<ref name="Raoult et al., 2004">{{cite journal |last1=Raoult |first1=Didier |first2=Stéphane |last2=Audic |first3=Catherine |last3=Robert |first4=Chantal |last4=Abergel |first5=Patricia |last5=Renesto |first6=Hiroyuki |last6=Ogata |first7=Bernard |last7=La Scola |first8=Marie |last8=Suzan |first9=Jean-Michel |last9=Claverie |title=The 1.2 megabase genome sequence of Mimivirus |journal=[[Science (journal)|Science]] |year=2004 |volume=306 |pages=1344–1350 |doi=10.1126/science.1101485 |bibcode=2004Sci...306.1344R |pmid=15486256 |issue=5700|s2cid=84298461 }}</ref> |
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== See also == |
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{{portal|Biology}} |
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* [[Cladistics]] |
* [[Cladistics]] |
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* [[Phylogenetics]] |
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* [[Systematics]] |
* [[Systematics]] |
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* [[Taxonomy (biology)|Taxonomy]] |
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== |
== Notes == |
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{{ |
{{notelist}} |
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== |
== References == |
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{{reflist|refs= |
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* [http://waynesword.palomar.edu/trfeb98.htm The five kingdom concept] |
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<ref name=Woese>{{cite journal |last1=Woese |first1=C.R. |last2=Kandler |first2=O. |last3=Wheelis |first3=M.L. |year=1990 |title=Towards a natural systs: proposal for the domains Archaea, Bacteria, and Eucarya |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=87 |issue=12 |pages=4576–9 |pmid=2112744 |pmc=54159 |doi=10.1073/pnas.87.12.4576 |bibcode=1990PNAS...87.4576W |doi-access=free}}</ref> |
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* [http://home.manhattan.edu/~frances.cardillo/plants/intro/plntlist.html Whittaker's classification] |
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}} |
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== Further reading == |
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{{Taxonomic ranks}} |
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* Pelentier, B. (2007-2015). ''Empire Biota: a comprehensive taxonomy'', [https://web.archive.org/web/20140202201721/http://www.empirebiota.info/]. [Historical overview.] |
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* [[Peter H. Raven]] and Helena Curtis (1970), ''Biology of Plants'', New York: Worth Publishers. [Early presentation of five-kingdom system.] |
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== External links == |
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{{DEFAULTSORT:rank01}} |
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* [https://earthlingnature.wordpress.com/2011/12/05/a-brief-history-of-the-kingdoms-of-life/ A Brief History of the Kingdoms of Life] at Earthling Nature |
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[[Category:Scientific classification]] |
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* [https://www2.palomar.edu/users/warmstrong/trfeb98.htm The five kingdom concept] {{Webarchive|url=https://web.archive.org/web/20211107151103/https://www2.palomar.edu/users/warmstrong/trfeb98.htm |date=2021-11-07 }} |
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[[Category:Botanical nomenclature]] |
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* [https://web.archive.org/web/20080105094632/http://home.manhattan.edu/~frances.cardillo/plants/intro/plntlist.html Whittaker's classification] |
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[[Category:Zoological nomenclature]] |
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{{Taxonomic ranks}} |
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{{DEFAULTSORT:Rank01}} |
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[[af:Koninkryk (biologie)]] |
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Latest revision as of 10:10, 4 November 2024
In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla (singular phylum).
Traditionally, textbooks from Canada and the United States have used a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaebacteria, and Bacteria or Eubacteria), while textbooks in other parts of the world, such as Bangladesh, Brazil, Greece, India, Pakistan, Spain, and the United Kingdom have used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera).
Some recent classifications based on modern cladistics have explicitly abandoned the term kingdom, noting that some traditional kingdoms are not monophyletic, meaning that they do not consist of all the descendants of a common ancestor. The terms flora (for plants), fauna (for animals), and, in the 21st century, funga (for fungi) are also used for life present in a particular region or time.[1][2]
Definition and associated terms
[edit]When Carl Linnaeus introduced the rank-based system of nomenclature into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: class, order, genus and species.[3] Later two further main ranks were introduced, making the sequence kingdom, phylum or division, class, order, family, genus and species.[4] In 1990, the rank of domain was introduced above kingdom.[5]
Prefixes can be added so subkingdom (subregnum) and infrakingdom (also known as infraregnum) are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain. In some classification systems the additional rank branch (Latin: ramus) can be inserted between subkingdom and infrakingdom, e.g., Protostomia and Deuterostomia in the classification of Cavalier-Smith.[6]
History
[edit]Two kingdoms of life
[edit]The classification of living things into animals and plants is an ancient one. Aristotle (384–322 BC) classified animal species in his History of Animals, while his pupil Theophrastus (c. 371–c. 287 BC) wrote a parallel work, the Historia Plantarum, on plants.[7]
Carl Linnaeus (1707–1778) laid the foundations for modern biological nomenclature, now regulated by the Nomenclature Codes, in 1735. He distinguished two kingdoms of living things: Regnum Animale ('animal kingdom') and Regnum Vegetabile ('vegetable kingdom', for plants). Linnaeus also included minerals in his classification system, placing them in a third kingdom, Regnum Lapideum.
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Three kingdoms of life
[edit]
In 1674, Antonie van Leeuwenhoek, often called the "father of microscopy", sent the Royal Society of London a copy of his first observations of microscopic single-celled organisms. Until then, the existence of such microscopic organisms was entirely unknown. Despite this, Linnaeus did not include any microscopic creatures in his original taxonomy.
At first, microscopic organisms were classified within the animal and plant kingdoms. However, by the mid–19th century, it had become clear to many that "the existing dichotomy of the plant and animal kingdoms [had become] rapidly blurred at its boundaries and outmoded".[8]
In 1860 John Hogg proposed the Protoctista, a third kingdom of life composed of "all the lower creatures, or the primary organic beings"; he retained Regnum Lapideum as a fourth kingdom of minerals.[8] In 1866, Ernst Haeckel also proposed a third kingdom of life, the Protista, for "neutral organisms" or "the kingdom of primitive forms", which were neither animal nor plant; he did not include the Regnum Lapideum in his scheme.[8] Haeckel revised the content of this kingdom a number of times before settling on a division based on whether organisms were unicellular (Protista) or multicellular (animals and plants).[8]
Four kingdoms
[edit]The development of microscopy revealed important distinctions between those organisms whose cells do not have a distinct nucleus (prokaryotes) and organisms whose cells do have a distinct nucleus (eukaryotes). In 1937 Édouard Chatton introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms.[9]
In 1938, Herbert F. Copeland proposed a four-kingdom classification by creating the novel Kingdom Monera of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as Bacteria and Archaea. Ernst Haeckel, in his 1904 book The Wonders of Life, had placed the blue-green algae (or Phycochromacea) in Monera; this would gradually gain acceptance, and the blue-green algae would become classified as bacteria in the phylum Cyanobacteria.[8][9]
In the 1960s, Roger Stanier and C. B. van Niel promoted and popularized Édouard Chatton's earlier work, particularly in their paper of 1962, "The Concept of a Bacterium"; this created, for the first time, a rank above kingdom—a superkingdom or empire—with the two-empire system of prokaryotes and eukaryotes.[9] The two-empire system would later be expanded to the three-domain system of Archaea, Bacteria, and Eukaryota.[10]
| Life | |
Five kingdoms
[edit]The differences between fungi and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification,[8] but was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the Fungi.[11] The resulting five-kingdom system, proposed in 1969 by Whittaker, has become a popular standard and with some refinement is still used in many works and forms the basis for new multi-kingdom systems. It is based mainly upon differences in nutrition; his Plantae were mostly multicellular autotrophs, his Animalia multicellular heterotrophs, and his Fungi multicellular saprotrophs.
The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies.[11] The five kingdom system may be combined with the two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as Lynn Margulis's system of five kingdoms, the plants included just the land plants (Embryophyta), and Protoctista has a broader definition.[12][page needed]
Following publication of Whittaker's system, the five-kingdom model began to be commonly used in high school biology textbooks.[13] But despite the development from two kingdoms to five among most scientists, some authors as late as 1975 continued to employ a traditional two-kingdom system of animals and plants, dividing the plant kingdom into subkingdoms Prokaryota (bacteria and cyanobacteria), Mycota (fungi and supposed relatives), and Chlorota (algae and land plants).[14]
| Life | |
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Kingdom Monera
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Kingdom Protista
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Kingdom Plantae
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Kingdom Fungi
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Kingdom Animalia
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Six kingdoms
[edit]In 1977, Carl Woese and colleagues proposed the fundamental subdivision of the prokaryotes into the Eubacteria (later called the Bacteria) and Archaebacteria (later called the Archaea), based on ribosomal RNA structure;[15] this would later lead to the proposal of three "domains" of life, of Bacteria, Archaea, and Eukaryota.[5] Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea.[16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus.[13] But the division of prokaryotes into two kingdoms remains in use with the recent seven kingdoms scheme of Thomas Cavalier-Smith, although it primarily differs in that Protista is replaced by Protozoa and Chromista.[17]
| Life |
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Eight kingdoms
[edit]Thomas Cavalier-Smith supported the consensus at that time, that the difference between Eubacteria and Archaebacteria was so great (particularly considering the genetic distance of ribosomal genes) that the prokaryotes needed to be separated into two different kingdoms. He then divided Eubacteria into two subkingdoms: Negibacteria (Gram-negative bacteria) and Posibacteria (Gram-positive bacteria). Technological advances in electron microscopy allowed the separation of the Chromista from the Plantae kingdom. Indeed, the chloroplast of the chromists is located in the lumen of the endoplasmic reticulum instead of in the cytosol. Moreover, only chromists contain chlorophyll c. Since then, many non-photosynthetic phyla of protists, thought to have secondarily lost their chloroplasts, were integrated into the kingdom Chromista.
Finally, some protists lacking mitochondria were discovered.[18] As mitochondria were known to be the result of the endosymbiosis of a proteobacterium, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom Archezoa. This superkingdom was opposed to the Metakaryota superkingdom, grouping together the five other eukaryotic kingdoms (Animalia, Protozoa, Fungi, Plantae and Chromista). This was known as the Archezoa hypothesis, which has since been abandoned;[19] later schemes did not include the Archezoa–Metakaryota divide.[6][17]
| Life |
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‡ No longer recognized by taxonomists.
Six kingdoms (1998)
[edit]In 1998, Cavalier-Smith published a six-kingdom model,[6] which has been revised in subsequent papers. The version published in 2009 is shown below.[20][a][21] Cavalier-Smith no longer accepted the importance of the fundamental Eubacteria–Archaebacteria divide put forward by Woese and others and supported by recent research.[22] The kingdom Bacteria (sole kingdom of empire Prokaryota) was subdivided into two sub-kingdoms according to their membrane topologies: Unibacteria and Negibacteria. Unibacteria was divided into phyla Archaebacteria and Posibacteria; the bimembranous-unimembranous transition was thought to be far more fundamental than the long branch of genetic distance of Archaebacteria, viewed as having no particular biological significance.
Cavalier-Smith does not accept the requirement for taxa to be monophyletic ("holophyletic" in his terminology) to be valid. He defines Prokaryota, Bacteria, Negibacteria, Unibacteria, and Posibacteria as valid paraphyla (therefore "monophyletic" in the sense he uses this term) taxa, marking important innovations of biological significance (in regard of the concept of biological niche).
In the same way, his paraphyletic kingdom Protozoa includes the ancestors of Animalia, Fungi, Plantae, and Chromista. The advances of phylogenetic studies allowed Cavalier-Smith to realize that all the phyla thought to be archezoans (i.e. primitively amitochondriate eukaryotes) had in fact secondarily lost their mitochondria, typically by transforming them into new organelles: Hydrogenosomes. This means that all living eukaryotes are in fact metakaryotes, according to the significance of the term given by Cavalier-Smith. Some of the members of the defunct kingdom Archezoa, like the phylum Microsporidia, were reclassified into kingdom Fungi. Others were reclassified in kingdom Protozoa, like Metamonada which is now part of infrakingdom Excavata.
Because Cavalier-Smith allows paraphyly, the diagram below is an 'organization chart', not an 'ancestor chart', and does not represent an evolutionary tree.
| Life |
| ||||||||||||||||||||||||||||||
Seven kingdoms
[edit]Cavalier-Smith and his collaborators revised their classification in 2015. In this scheme they introduced two superkingdoms of Prokaryota and Eukaryota and seven kingdoms. Prokaryota have two kingdoms: Bacteria and Archaea. (This was based on the consensus in the Taxonomic Outline of Bacteria and Archaea, and the Catalogue of Life). The Eukaryota have five kingdoms: Protozoa, Chromista, Plantae, Fungi, and Animalia. In this classification a protist is any of the eukaryotic unicellular organisms.[17]
| Life |
| |||||||||||||||||||||||||||
Summary
[edit]| Linnaeus 1735[23] |
Haeckel 1866[24] |
Chatton 1925[25][26] |
Copeland 1938[27][28] |
Whittaker 1969[29] |
Woese et al. 1977[30][31] |
Woese et al. 1990[32] |
Cavalier-Smith 1993[33][34][35] |
Cavalier-Smith 1998[36][37][38] |
Ruggiero et al. 2015[39] |
|---|---|---|---|---|---|---|---|---|---|
| — | — | 2 empires | 2 empires | 2 empires | 2 empires | 3 domains | 3 superkingdoms | 2 empires | 2 superkingdoms |
| 2 kingdoms | 3 kingdoms | — | 4 kingdoms | 5 kingdoms | 6 kingdoms | — | 8 kingdoms | 6 kingdoms | 7 kingdoms |
| — | Protista | Prokaryota | Monera | Monera | Eubacteria | Bacteria | Eubacteria | Bacteria | Bacteria |
| Archaebacteria | Archaea | Archaebacteria | Archaea | ||||||
| Eukaryota | Protista | Protista | Protista | Eucarya | Archezoa | Protozoa | Protozoa | ||
| Protozoa | |||||||||
| Chromista | Chromista | Chromista | |||||||
| Vegetabilia | Plantae | Plantae | Plantae | Plantae | Plantae | Plantae | Plantae | ||
| Fungi | Fungi | Fungi | Fungi | Fungi | |||||
| Animalia | Animalia | Animalia | Animalia | Animalia | Animalia | Animalia | Animalia |
The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach:
- Kingdoms such as Protozoa represent grades rather than clades, and so are rejected by phylogenetic classification systems.
- The most recent research does not support the classification of the eukaryotes into any of the standard systems. As of April 2010[update], no set of kingdoms is sufficiently supported by research to attain widespread acceptance. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."[40]
Beyond traditional kingdoms
[edit]While the concept of kingdoms continues to be used by some taxonomists, there has been a movement away from traditional kingdoms, as they are no longer seen as providing a cladistic classification, where there is emphasis in arranging organisms into natural groups.[41]
Three domains of life
[edit]
Based on RNA studies, Carl Woese thought life could be divided into three large divisions and referred to them as the "three primary kingdom" model or "urkingdom" model.[15]
In 1990, the name "domain" was proposed for the highest rank.[5] This term represents a synonym for the category of dominion (lat. dominium), introduced by Moore in 1974.[42] Unlike Moore, Woese et al. (1990) did not suggest a Latin term for this category, which represents a further argument supporting the accurately introduced term dominion.[43]
Woese divided the prokaryotes (previously classified as the Kingdom Monera) into two groups, called Eubacteria and Archaebacteria, stressing that there was as much genetic difference between these two groups as between either of them and all eukaryotes.
| Life |
| |||||||||
According to genetic data, although eukaryote groups such as plants, fungi, and animals may look different, they are more closely related to each other than they are to either the Eubacteria or Archaea. It was also found that the eukaryotes are more closely related to the Archaea than they are to the Eubacteria. Although the primacy of the Eubacteria-Archaea divide has been questioned, it has been upheld by subsequent research.[22] There is no consensus on how many kingdoms exist in the classification scheme proposed by Woese.
Eukaryotic supergroups
[edit]
In 2004, a review article by Simpson and Roger noted that the Protista were "a grab-bag for all eukaryotes that are not animals, plants or fungi". They held that only monophyletic groups should be accepted as formal ranks in a classification and that – while this approach had been impractical previously (necessitating "literally dozens of eukaryotic 'kingdoms'") – it had now become possible to divide the eukaryotes into "just a few major groups that are probably all monophyletic".[41]
On this basis, the diagram opposite (redrawn from their article) showed the real "kingdoms" (their quotation marks) of the eukaryotes.[41] A classification which followed this approach was produced in 2005 for the International Society of Protistologists, by a committee which "worked in collaboration with specialists from many societies". It divided the eukaryotes into the same six "supergroups".[44] The published classification deliberately did not use formal taxonomic ranks, including that of "kingdom".
| Life |
| ||||||||||||||||||||||||||||||||||||
In this system the multicellular animals (Metazoa) are descended from the same ancestor as both the unicellular choanoflagellates and the fungi which form the Opisthokonta.[44] Plants are thought to be more distantly related to animals and fungi.
However, in the same year as the International Society of Protistologists' classification was published (2005), doubts were being expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata,[45] and a review in 2006 noted the lack of evidence for several of the six proposed supergroups.[46]
As of 2010[update], there is widespread agreement that the Rhizaria belong with the Stramenopiles and the Alveolata, in a clade dubbed the SAR supergroup,[47] so that Rhizaria is not one of the main eukaryote groups.[20][48][49][50][51] Beyond this, there does not appear to be a consensus. Rogozin et al. in 2009 noted that "The deep phylogeny of eukaryotes is an extremely difficult and controversial problem."[52] As of December 2010[update], there appears to be a consensus that the six supergroup model proposed in 2005 does not reflect the true phylogeny of the eukaryotes and hence how they should be classified, although there is no agreement as to the model which should replace it.[48][49][53]
Comparison of top level classification
[edit]Some authors have added non-cellular life to their classifications. This can create a "superdomain" called "Acytota", also called "Aphanobionta", of non-cellular life; with the other superdomain being "cytota" or cellular life.[54][55] The eocyte hypothesis proposes that the eukaryotes emerged from a phylum within the archaea called the Thermoproteota (formerly known as eocytes or Crenarchaeota).[56][57]
| Taxonomical root node | Two superdomains (controversial) | Two empires | Three domains | Five Dominiums[58] | Five kingdoms | Six kingdoms | Eocyte hypothesis |
|---|---|---|---|---|---|---|---|
| Biota / Vitae / Life | Acytota / Aphanobionta non-cellular life |
Virusobiota (Viruses, Viroids) | |||||
| Prionobiota (Prions) | |||||||
| Cytota cellular life |
Prokaryota / Procarya (Monera) |
Bacteria | Bacteria | Monera | Eubacteria | Bacteria | |
| Archaea | Archaea | Archaebacteria | Archaea including eukaryotes | ||||
| Eukaryota / Eukarya | Protista | ||||||
| Fungi | |||||||
| Plantae | |||||||
| Animalia | |||||||
Viruses
[edit]The International Committee on Taxonomy of Viruses uses the taxonomic rank "kingdom" in the classification of viruses (with the suffix -virae); but this is beneath the top level classifications of realm and subrealm.[59]
There is ongoing debate as to whether viruses can be included in the tree of life. The arguments against include the fact that they are obligate intracellular parasites that lack metabolism and are not capable of replication outside of a host cell.[60][61] Another argument is that their placement in the tree would be problematic, since it is suspected that viruses have various evolutionary origins,[60] and they have a penchant for harvesting nucleotide sequences from their hosts.
On the other hand, there are arguments in favor of their inclusion.[62] One of these comes from the discovery of unusually large and complex viruses, such as Mimivirus, that possess typical cellular genes.[63]
See also
[edit]
Notes
[edit]- ^ Compared to the version Cavalier-Smith published in 2004, the alveolates and the rhizarians have been moved from Kingdom Protozoa to Kingdom Chromista.
References
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Further reading
[edit]- Pelentier, B. (2007-2015). Empire Biota: a comprehensive taxonomy, [1]. [Historical overview.]
- Peter H. Raven and Helena Curtis (1970), Biology of Plants, New York: Worth Publishers. [Early presentation of five-kingdom system.]
External links
[edit]- A Brief History of the Kingdoms of Life at Earthling Nature
- The five kingdom concept Archived 2021-11-07 at the Wayback Machine
- Whittaker's classification