Taxon

taxagrouppolytypictaxonomic groupsubtaxagroupssubtaxontaxonsanimal formsanimal group
In biology, a taxon (plural taxa; back-formation from taxonomy) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit.wikipedia
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Class (biology)

classsubclassclasses
An example of a well-established taxon that is not also a clade is the class Reptilia, the reptiles; birds are descendants of reptiles but are not included in the Reptilia.Birds are included in the Aves.
In biological classification, class (classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank.

Clade

cladesgroupcladistic
Their basic unit, therefore, is the clade rather than the taxon. This has given rise to phylogenetic taxonomy and the ongoing development of the PhyloCode, which has been proposed as a new alternative to replace Linnean classification and govern the application of names to clades.
Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic.

International Code of Zoological Nomenclature

ICZNzoological nomenclatureICZN Code
The Glossary of the International Code of Zoological Nomenclature (1999) defines a *"taxon, (pl. taxa), n. The use of a narrow set of ranks is challenged by users of cladistics; for example, the mere 10 ranks traditionally used between animal families (governed by the ICZN) and animal phyla (usually the highest relevant rank in taxonomic work) often cannot adequately represent the evolutionary history as more about a lineage's phylogeny becomes known.
The code is meant to guide only the nomenclature of animals, while leaving zoologists freedom in classifying new taxa.

Monophyly

monophyleticmonophyletic groupnon-monophyletic
Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic (all descendants of some ancestor).
Further, any group may (or may not) be considered a taxon by modern systematics, depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams.

Fungus

Fungifungalnecrotrophic
"Phylum" applies formally to any biological domain, but traditionally it was always used for animals, whereas "Division" was traditionally often used for plants, fungi, etc.
The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, and morphologies ranging from unicellular aquatic chytrids to large mushrooms.

Plant

Plantaeplantsflora
"Phylum" applies formally to any biological domain, but traditionally it was always used for animals, whereas "Division" was traditionally often used for plants, fungi, etc.
When the name Plantae or plant is applied to a specific group of organisms or taxon, it usually refers to one of four concepts.

Phylogenetic nomenclature

stem-based taxonphylogenetic taxonomyphylogenetic classification
Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic (all descendants of some ancestor). This has given rise to phylogenetic taxonomy and the ongoing development of the PhyloCode, which has been proposed as a new alternative to replace Linnean classification and govern the application of names to clades.
Phylogenetic nomenclature, often called cladistic nomenclature, is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below.

Taxonomy (biology)

taxonomictaxonomytaxonomist
In biology, a taxon (plural taxa; back-formation from taxonomy) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit.
Organisms are grouped together into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a super-group of higher rank, thus creating a taxonomic hierarchy.

Chresonym

heterochresonymorthochresonym
In biodiversity informatics, a chresonym is the cited use of a taxon name, usually a species name, within a publication.

Ichnotaxon

ichnogenusichnospeciesichnotaxa
An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact.

Taxonomic rank

superfamilysuperfamiliesrank
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.
In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in a taxonomic hierarchy.

PhyloCode

ICPNInternational Code of Phylogenetic Nomenclaturestem-based
This has given rise to phylogenetic taxonomy and the ongoing development of the PhyloCode, which has been proposed as a new alternative to replace Linnean classification and govern the application of names to clades.
The rank-based codes define taxa using a rank (such as genus, family, etc.) and, in many cases, a type specimen or type subtaxon.

Virus classification

viral speciessubviral agentBaltimore classification
The system shares many features with the classification system of cellular organisms, such as taxon structure.

Marchantiophyta

liverwortliverwortsHepaticae
For example, liverworts have been grouped, in various systems of classification, as a family, order, class, or division (phylum).
In addition to this taxon-based name, the liverworts are often called Hepaticophyta.

ABCD Schema

ABCDEFG Schema
The Access to Biological Collections Data (ABCD) schema is a highly structured data exchange and access model for taxon occurrence data (specimens, observations, etc. of living organisms), i.e. primary biodiversity data.

International Code of Nomenclature for algae, fungi, and plants

International Code of Botanical NomenclatureICBNICN
Many cladists do not see any need to depart from traditional nomenclature as governed by the ICZN, ICN, etc.

Phenetics

pheneticpheneticallyphenetic analyses
In addition, the class rank is quite often not an evolutionary but a phenetic or paraphyletic group and as opposed to those ranks governed by the ICZN (family-level, genus-level and species-level taxa), can usually not be made monophyletic by exchanging the taxa contained therein.
While a major goal of taxonomy remains describing the 'tree of life' – the evolutionary path connecting all species – in fieldwork one needs to be able to separate one taxon from another.

Phylogenetic tree

phylogenyphylogeneticevolutionary tree
The use of a narrow set of ranks is challenged by users of cladistics; for example, the mere 10 ranks traditionally used between animal families (governed by the ICZN) and animal phyla (usually the highest relevant rank in taxonomic work) often cannot adequately represent the evolutionary history as more about a lineage's phylogeny becomes known.
In these types of analysis, the output tree of a phylogenetic analysis of a single gene is an estimate of the gene's phylogeny (i.e. a gene tree) and not the phylogeny of the taxa (i.e. species tree) from which these characters were sampled, though ideally, both should be very close.

Segregate (taxonomy)

segregatedsegregatetaxonomic split
In taxonomy, a segregate, or a segregate taxon is created when a taxon is split off from another taxon.

Biology

biologicalBiological Sciencesbiologist
In biology, a taxon (plural taxa; back-formation from taxonomy) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit.

Back-formation

back formationback-formedbackformation
In biology, a taxon (plural taxa; back-formation from taxonomy) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit.

Nomenclature codes

specific epithetbiological nomenclaturenomenclature code
If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Carl Linnaeus

LinnaeusL.Carl von Linné
Initial attempts at classifying and ordering organisms (plants and animals) were set forth in Linnaeus's system in Systema Naturae, 10th edition, (1758) as well as an unpublished work by Bernard and Antoine Laurent de Jussieu.

Systema Naturae

1758Systema Naturæ1789
Initial attempts at classifying and ordering organisms (plants and animals) were set forth in Linnaeus's system in Systema Naturae, 10th edition, (1758) as well as an unpublished work by Bernard and Antoine Laurent de Jussieu.

Bernard de Jussieu

BernardJussieu
Initial attempts at classifying and ordering organisms (plants and animals) were set forth in Linnaeus's system in Systema Naturae, 10th edition, (1758) as well as an unpublished work by Bernard and Antoine Laurent de Jussieu.