Autapomorphy

An autapomorphy in cladistics is a derived trait or apomorphy that is unique to only one terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group (which may be a species, family or in general any clade).

An autapomorphy is not present in the closest relative of the terminal group and also was not present in their common ancestor.