What is "crown group"

n. (context phylogenetics English) The living representatives of a collection of species, together with their ancestors back to their most recent common ancestor as well as all of that ancestor's descendants.

In phylogenetics, the crown group of a collection of species consists of the living representatives of the collection together with their ancestors back to their most recent common ancestor as well as all of that ancestor's descendants. It is thus a clade, a group consisting of a species and all its descendants.

The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen.