What is "paraphyly"

n. (context systematics English) The condition of being paraphyletic

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two— monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups. The term is commonly used in phylogenetics (a subfield of biology) and in linguistics.

The term was coined to apply to well-known taxa like reptiles (Reptilia) which, as commonly named and traditionally defined, is paraphyletic with respect to mammals and birds. Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor—including all extant reptiles as well as the extinct synapsids—except for mammals and birds. Other commonly recognized paraphyletic groups include fish and lizards.

If many subgroups are missing from the named group, it is said to be polyparaphyletic. A paraphyletic group cannot be a clade, which is a monophyletic group.