These authors consulted more than sources see S1 Appendix , most of which were from recent taxonomic publications and websites. In achieving a consensus, the panel was required to make some compromises that may require future revision as the related issues are resolved. While all of these individuals made contributions to the hierarchy, not all necessarily endorse every aspect of it.
The CoL classification will undergo review and revision at five-year intervals to consider changes as necessary. For each of these kingdoms we had to exercise our taxonomic judgment and reach a practical compromise among diverse opinions and usages and conflicting evidence about certain phylogenetic questions important for defining the boundaries between and ranks of major taxa, including kingdoms.
Our schema includes: the prokaryotic kingdoms Archaea Archaebacteria and Bacteria Eubacteria , and the eukaryotic kingdoms Protozoa, Chromista, Fungi, Plantae, and Animalia. We have retained 14 ranks from superkingdom to order Table 1.
Several key taxonomic issues, some not fully resolved, are discussed below. The higher classification of prokaryotes is still somewhat unsettled. Margulis and Schwartz [ 28 ] recognized the superkingdom Prokarya, containing one kingdom Bacteria that included a subkingdom Archaea; Cavalier-Smith also treated Archaebacteria and Eubacteria as prokaryote subkingdoms [ 19 , 29 ].
While these sources list the names of phyla in common use as a service to the user, they are not validly published under the ICNB. We have not placed phylum names in quotation marks as they have but we have so designated a few prokaryote names at lower ranks that are in common use but not or not yet valid. As no prokaryote names above the ranks of class are covered by ICNB rules, there is no official higher classification of prokaryotes [ 32 ] and any attempt at such is necessarily difficult.
We have chosen to adopt the classification in current use by the Catalogue of Life. We treat them as de facto kingdoms until there is a better resolution of their status. Greater use of multigene trees rather than over reliance on rRNA gene trees alone may eventually allow further simplification by grouping them into fewer phyla, possibly only about half the present number [ 28 ].
Unicellular eukaryotes, usually called protists, comprise a polyphyletic group of eukaryotes that do not undergo tissue formation through the process of embryological layering. They include ancestrally unicellular eukaryotes directly descended from bacteria by the origin of the nucleus, endomembrane, cytoskeleton, and mitochondria.
Assigning them to separate kingdoms was historically difficult when only light microscopy was available but is now considerably facilitated because of advances in electron microscopy and gene sequencing.
Formerly, the unicellular amoeboid group Myxozoa with multicellular spores was included in Protozoa but these protists are now firmly within the animal kingdom, having been proven to be greatly simplified parasitic animals. Yeasts are unicellular fungi that evolved polyphyletically from multicellular filamentous ancestors and are assigned to one of three higher fungal phyla. Microsporidia are highly reduced intracellular parasites traditionally considered to be Protozoa, but they have been known for two decades to be related to Fungi.
At one time it was thought microsporidia had evolved from Fungi and therefore were placed in that kingdom [ 19 , 33 ]. For several years multigene trees were contradictory about whether microsporidia branched within or diverged from Fungi. The latest evidence is that they are most closely related to rozellids [ 34 ], which also have been treated either as Fungi or Protozoa. If this recent phylogeny [ 34 ] is correct, both should be in the same kingdom. Here we take the view that the best demarcation between Protozoa and Fungi lies immediately before the origin of the chitinous wall around vegetative fungal cells and associated loss of phagotrophy [ 33 ].
We therefore include microsporidia and rozellids in Protozoa vegetatively wall-less, typically phagotrophs not Fungi vegetatively walled osmotrophs. For decades, taxonomists have debated the boundary between Protozoa and Plantae. We accept the view that it should be placed just prior to the evolutionary origin of chloroplasts and that Plantae should comprise all eukaryotes with plastids directly descending from the initially enslaved cyanobacterium, i.
Therefore, all green algae are included in Viridiplantae and Plantae and are excluded from Protozoa. The only photosynthetic Protozoa are Euglenophyceae, which obtained their chloroplasts subsequently from an enslaved green alga [ 21 ].
The boundary between Protozoa and Chromista has been more controversial. Chromista was established to include all chromophyte algae those with chlorophyll c , not b considered to have evolved by symbiogenetic enslavement of another eukaryote a red alga as well as all heterotrophic protists descended from them by loss of photosynthesis or entire plastids [ 35 ]. With phylogenetic advances it has become clearer that alveolates once considered Protozoa are related to chromistan heterokont algae and related heterotrophic heterokonts and more distantly to Rhizaria, the three together forming the major group Harosa equivalent to SAR.
Consequently, Chromista has been greatly expanded to include all Harosa as well as other former protozoa that turned out to be related to haptophytes or cryptophytes. Chromista now includes many groups once treated as Protozoa [ 19 ], an expansion followed here. In multigene trees, this expansion is the most difficult part of the entire eukaryote tree to resolve. They sometimes show one or both of Plantae and Chromista as a clade but often their major subgroups are intermingled in contradictory ways [ 36 , 37 ].
This may be a consequence of the eukaryote-eukaryote chimaeric history of chromists that acquired some genes from red algae or of the very rapid basal radiation of the robust corticate clade i. Plantae plus Chromista. Because of this, some question whether Chromista represents a clade, yet trees are still too poorly resolved to eliminate the likelihood from cell evolutionary considerations that Chromista and Plantae are genuinely distinct sister clades.
Evidence that Harosa is a clade is very strong. Evidence that Haptista plus Cryptista are a clade Hacrobia is strong on some trees but questioned by others [ 37 ]. Protozoa, like Prokaryota, is certainly a paraphyletic taxon [ 38 ]; Animalia, Fungi, Plantae, and Chromista all evolved from it. In our hierarchy Protozoa comprises seven phyla, of which four are probably clades and three paraphyletic. We do not consider it useful in a general classification to subdivide the paraphyletic phyla into numerous smaller ones, often with only a handful of species that most have never heard of, even though a few specialists might favor that despite their constituent subgroups not differing radically in cell structure.
For both Protozoa and Chromista we have favored large groups with shared body plans, analogous to extremely diverse animal phyla like Chordata and Arthropoda.
The higher proportion of ancestral paraphyletic phyla in Protozoa compared with terminal groups like animals and plants is unsurprising because they were the first eukaryotes and they diverged early on but with many fewer associated major changes in body plan than occurred during the much later radiation of bilateral animals. Distinct early diverging protozoan clades can be remarkably similar morphologically and biologically [ 39 ].
As stated earlier, we take the view that the best demarcation between Protozoa and Fungi lies immediately before the origin of the chitinous wall around vegetative fungal cells and associated loss of phagotrophy.
We use an updated version of the higher classification presented in the 10 th Edition of the Dictionary of Fungi [ 40 ]. The evolutionarily convergent Oomycetes such as the serious pest Phytophthora , formerly treated as Fungi, belong instead in phylum Pseudofungi of the heterokont Chromista. As with the other kingdoms, Plantae is classified in a variety of ways. Margulis and Schwartz [ 28 ] restricted Plantae to land plants embryophytes or higher plants and popularized the use of kingdom Protoctista to include lower plants green, red, and glaucophyte algae and lower Fungi as well as chromists with classical protozoa.
Many now consider such a kingdom too broad and heterogeneous and the associated separation of lower and higher plants in different kingdoms to be undesirable. Now taxonomists almost universally classify lower and higher plants together in the single kingdom Plantae and lower and higher fungi within the single kingdom Fungi. We have adopted this delimitation of Plantae here [ 19 , 35 ] for which Archaeplastida [ 12 , 18 ] is a less familiar recent synonym.
The structure of plastid genomes and the derived chloroplast protein-import machinery support a single origin of glaucophytes, red algae, green algae, and embryophytes land plants. The ancestral embryophyte is thought to have originated from relatives of the Charales stoneworts or Coleochaetales Charophyta. Jeffrey [ 41 ] first grouped charophytes and embryophytes as a clade Streptophyta, which was later validated as a superphylum [ 42 ] and reduced to phylum by Bremer [ 43 ].
Here we recognize four embryophyte phyla—three of bryophytes liverworts, hornworts, and mosses and a single phylum Tracheophyta for vascular plants—with all species characterized by a diploid phase having xylem and phloem. This diagram shows the levels of taxonomic hierarchy for a dog, from the broadest category—domain—to the most specific—species.
Click for a larger image. The kingdom Animalia stems from the Eukarya domain. For the common dog, the classification levels would be as shown in Figure 1. Therefore, the full name of an organism technically has eight terms. Notice that each name is capitalized except for species, and the genus and species names are italicized.
Scientists generally refer to an organism only by its genus and species, which is its two-word scientific name, in what is called binomial nomenclature. Each species has a unique binomial to allow for proper identification. Therefore, the scientific name of the dog is Canis lupus. It is important that the correct formatting capitalization and italics is used when calling an organism by its specific binomial.
The name at each level is also called a taxon. Because they share so much in common, organisms of a family are said to be related to each other. Genus is a way to describe the generic name for an organism. The genus classification is very specific so there are fewer organisms within each one. For this reason, there are a lot of different genera among both animals and plants. When using taxonomy to name an organism, the genus is used to determine the first part of its two-part name.
Species are as specific as you can get. It is the lowest and most strict level of classification of living things. The main criteria for an organism to be placed in a particular species is the ability to breed with other organisms of that same species.
The species of an organism determines the second part of its two-part name. The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands. Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden.
This website uses cookies to ensure you get the best experience on our website. Learn more. Skip to main content Skip to acknowledgement of country Skip to footer On this page Toggle Table of Contents Nav What is classification?
Levels of classification.
0コメント