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The highest ranking of organisms in the standard . The term is based on earlier medieval and alchemical ideas - e.g. "animal kingdom" "vegetable kingdom," "mineral kingdom". The original Plant - Animal Kingdom divide was replaced by the of and . Modern research into micro-organisms however has shown that they are far more diverse than was previously thought, and the kingdom has been relegated to a relatively minor status vis a vis the , the highest current taxonomic ranking.
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In , a kingdom or regnum is the top-level, or nearly the top-level, of organisms in .
In his , first published in 1735, distinguished two kingdoms of living things: Animalia for and Vegetabilia for (Linnaeus also treated , placing them in a third kingdom, Mineralia). Linnaeus divided each kingdom into classes, later grouped into for animals and for plants.
When single-celled organisms were first discovered, they were split between the two kingdoms: mobile forms in the animal phylum , and colored and in the plant division Thallophyta or Protophyta. However, a number of forms were hard to place, or were placed in different kingdoms by different authors: for example, the mobile alga and the amoeba-like . As a result, suggested creating a third kingdom for them [1] [2].
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The discovery that have a radically different cell structure from other organisms — bacteria are contained in a single , whereas other organisms have a more complex structure with a and other divided by intracellular membranes — led Chatton to propose a division of life into organisms with a nucleus in and organisms without in [3]although this was already known and it was Novak(1930) who formally named and ranked them as superkingdoms but used the names Akaryonta and Karyonta. Dougherty (1957) formally named them Prokaryota and Eukaryota.
Chatton's proposal was not taken up immediately; a more typical system was that of , who gave the prokaryotes a separate kingdom, originally called Mychota but later referred to as or Bacteria [4]. Copeland's four-kingdom system placed all eukaryotes other than animals and plants in the kingdom [5].
It gradually became apparent how important the prokaryote/eukaryote distinction is, and Stanier and van Niel popularized Chatton's proposal in the 1960s [6].
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recognized an additional kingdom for the . The resulting five-kingdom system, proposed in 1969, has become a popular standard and with some refinement is still used in many works, or forms the basis for newer multi-kingdom systems. It is based mainly on differences in : his Plantae were mostly multicellular , his Animalia multicellular , and his Fungi multicellular . The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies [7].
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In the years around 1980 there was an emphasis on and redefining the kingdoms to be . The Animalia, Plantae, and Fungi were generally reduced to core groups of closely related forms, and the others thrown into the Protista. Based on studies divided the prokaryotes into two kingdoms, called and . Such six-kingdom systems have become standard in many works [8]
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 proposed by , including organisms such as , , and . Thus the eukaryotes are divided into three primarily heterotrophic groups, the Animalia, Fungi, and Protozoa, and two primarily photosynthetic groups, the Plantae (including ) and Chromista. However, it has not become widely used because of uncertainty over the monophyly of the latter two kingdoms.
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| Linnaeus 1735 2 kingdoms | Haeckel 1866 [1] 3 kingdoms | Chatton 1937 [2] 2 groups | Copeland 1956 [5] 4 kingdoms | Whittaker 1969< [7] 5 kingdoms | Woese et al. 1977 [8] 6 kingdoms | Woese et al. 1990 [9] 3 domains |
|---|---|---|---|---|---|---|
| (not treated) | ||||||
(Note that the equivalences in this table are not perfect. For example, Haeckel placed the red algae (Haeckel's Florideae; modern ) and blue-green algae (Haeckel's Archephyta; modern ) in his Plantae, but in modern classifications they are considered protists and bacteria respectively. However, despite this and other failures of equivalence, the table gives a useful simplification.)
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[1] E. Haeckel (1866). Generelle Morphologie der Organismen. Reimer, Berlin.
[2] Joseph M. Scamardella (1999). "Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista". International Microbiology 2: 207–221.
[3] E. Chatton (1937). Titres et travaux scientifiques. Sette, Sottano, Italy.
[4] H. F. Copeland (1938). "The kingdoms of organisms". Quart. Rev. Biol. 13: 383–420.
[5] H. F. Copeland (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books.
[6] R. Y. Stanier and C. B. van Niel (1962). "The concept of a bacterium". Arch. Microbiol. 42: 17–35.
[7] R. H. Whittaker (1969). "New concepts of kingdoms of organisms". Science 163: 150–160.
[8] C. R. Woese, W. E. Balch, L. J. Magrum, G. E. Fox and R. S. Wolfe (1977). "An ancient divergence among the bacteria". Journal of Molecular Evolution 9: 305–311.
[9] C. R. Woese, O. Kandler, and M. L. Wheelis, (1990) Towards a Natural System of Organisms: proposal for the domains Archaea, Bacteria, and Eucarya. Proceedings of the National Academy of Sceinces 87:4576-4579