An evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group and therefore cannot be used as a diagnostic or defining character for the group.

For example, vertebrae are found in zebras, cheetahs, and orangutans; but the common ancestor in which this trait first evolved is so distant that the trait is shared by many other animals. As a result, possession of vertebrae sheds no light on the phylogenetic relations of these three species.