paraphyletic

This term is a specialized technical descriptor used almost exclusively in phylogenetics and evolutionary biology. It describes a group that is "incomplete" from a cladistic perspective because it leaves out one or more descendant lineages, often because those descendants evolved distinct traits that led taxonomists to place them in a separate group.

In modern systematic biology, paraphyletic groups are generally avoided in favor of monophyletic groups (clades), which include the ancestor and all descendants. For example, the traditional group "Reptilia" is paraphyletic if birds are excluded, as birds are descendants of the same common ancestor as crocodiles and lizards.