Taxonomic categories

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Taxonomic categories

Any one of a number of formal ranks used for organisms in a traditional Linnaean classification. Biological classifications are orderly arrangements of organisms in which the order specifies some relationship. Taxonomic classifications are usually hierarchical and comprise nested groups of organisms. The actual groups are termed taxa. In the hierarchy, a higher taxon may include one or more lower taxa, and as a result the relationships among taxa are expressed as a divergent hierarchy that is formally represented by tree diagrams. In Linnaean classifications, taxonomic categories are devices that provide structure to the hierarchy of taxa without the use of tree diagrams. By agreement, there is a hierarchy of categorical ranks for each major group of organisms, beginning with the categories of highest rank and ending with categories of lowest rank, and while it is not necessary to use all the available categories, they must be used in the correct order (see table).

Conceptually, the hierarchy of categories is different than the hierarchy of taxa. For example, the taxon Cnidaria, which is ranked as a phylum, includes the classes Anthozoa (anemones), Scyphozoa (jellyfishes), and Hydrozoa (hydras). Cnidaria is

Categories commonly used in botanical and zoological classifications, from highest to lowest rank
Botanical categories Zoological categories
Divisio Phylum
Classis Class
Ordo Order
Familia Family
Genus Genus
Species Species

a particular and concrete group that is composed of parts. Anthozoa is part of, and included in, Cnidaria. However, categorical ranks are quite different. The category “class” is not part of, nor included in, the category “phylum.” Rather, the category “class” is a shelf in the hierarchy, a roadmark of relative position. There are many animal taxa ranked as classes, but there is only one “class” in the Linnaean hierarchy. This is an important strength of the system because it provides a way to navigate through a classification while keeping track of relative hierarchical levels with only a few ranks for a great number of organisms.

When Linnaeus invented his categories, there were only class, order, family, genus, and species. These were sufficient to serve the needs of biological diversity in the late eighteenth century, but were quite insufficient to classify the increasing number of species discovered since 1758. As a result, additional categorical levels have been created. These categories may use prefixes, such as super- and sub-, as well as new basic levels such as tribe. An example of a modern expanded botanical hierarchy of ranks between family and species is:












Linnaean categories are the traditional devices used to navigate the hierarchy of taxa. But categories are only conventions, and alternative logical systems, such as those used by phylogenetic systematists (cladists), are frequently used. See Animal systematics, Classification, biological, Phylogeny, Plant taxonomy, Zoological nomenclature

References in periodicals archive ?
Each of the selected papers was read and then classified according to the various classifications comprising the five chosen taxonomic categories.
We focus on two particularly important issues that arise from the inappropriate use of local system data to classify whole systems: (1) the paper's methodology introduces a bias in the assignment of systems to taxonomic categories and (2) the paper makes an unsupported assumption that local service configurations serve as proxies for the structures of whole systems.
1 (1) Because the %0 is a nonadditive index (Cortes, 1997) for grouping fish items into higher taxonomic categories (i.
8) (Later I will discuss how this taxonomic philosophy can be extended to lower taxonomic categories such as subspecies.
Our results provide little solace for evolutionists and ecologists attempting to classify individuals in hybrid zones into finely divided taxonomic categories and to discriminate between advanced backcrosses and pure species.
Firstly, we surveyed the fields concerning the taxonomic categories of the soil (Order, Suborder, Great Group and Subgroup) and selected those classes indicating the involvement of hydromorphic processes in soil origin and development.
Higher taxonomic categories of gekkonid lizards and their evolution.
Following pretests, locally appropriate taxonomic categories were derived from accepted local terms for animals.