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In biology, taxonomic rank (which some authors prefer to call nomenclatural rank [1] because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of organisms (a taxon) in a hierarchy that reflects evolutionary relationships.
If G is a crystallographic point group, then rank(G) is up to 3. [9] If G is a wallpaper group, then rank(G) = 2 to 4. The only wallpaper-group type of rank 4 is p2mm. [10] If G is a 3-dimensional space group, then rank(G) = 2 to 6. The only space-group type of rank 6 is Pmmm. [11]
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 biology, a taxon (back-formation from taxonomy; pl.: taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking , especially if and when it is accepted or becomes established.
A supergroup, in evolutionary biology, is a large group of organisms that share one common ancestor and have important defining characteristics. It is an informal, mostly arbitrary rank in biological taxonomy that is often greater than phylum or kingdom, although some supergroups are also treated as phyla. [1]
In botany, the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. [7] Any number of further ranks can be used as long as they are clearly defined. [7] The superorder rank is commonly used, with the ending -anae that was initiated by Armen Takhtajan's publications from 1966 onwards. [8]
In biological phylogenetics, a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group, [1] is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. [2]
Life is divided into domains, which are subdivided into further groups. Intermediate minor rankings are not shown. In biological taxonomy, a domain (/ d ə ˈ m eɪ n / or / d oʊ ˈ m eɪ n /) (Latin: regio [1]), also dominion, [2] superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together.