Autapomorphy

In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given 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). It can therefore be considered an apomorphy in relation to a single taxon. The word "autapomorphy" is derived from the Greek words αὐτός, aut = self; ἀπό, apo = away from; and μορφή, morphe = shape.