[[File:Monophyletic.svg|thumb|334px|A vertical cladogram showing one clade, ''vertebrata'', in which are nested others. Shown in blue is the clade [[Sauropsida]]. The traditional Linnaean taxonomic class [[Reptilia]] does not include [[Aves]] or [[Mammalia]], and does not form clade.]]
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A '''clade''' (from [[ancient Greek]] ''{{Polytonic|κλάδος}}'', ''klados'', "branch") is a technical term coined by [[GermanyEngland|GermanEnglish]] biologist [[WilliJulian HennigHuxley]] and used in biological [[systematics]] to signify a single "branch" on the "[[Tree of life (science)|Tree of life]]", a group composed of a single ancestor and all its descendants.<ref>{{cite bookjournal | last=HenningDupuis | first=W.Claude | year=19591984 | title=GrundzügeWilli einerHennig's Theorieimpact deron phylogenetischentaxonomic thought Systematik|language journal=GermanAnnual Review of Ecology and Systematics |publisher volume=Deutscher15 Zentralverlag|location pages=[[Berlin]]1–24 | issn=0066-4162}}</ref> The idea that such a "natural group" of organisms should be grouped together and given a [[Taxonomy|taxonomic]] name is central to [[biological classification]]. In [[cladistics]] (which takes it's name from the term), clades are the only acceptable units.
