Biologists distinguish three different types of character: homoplasy, shared derived character and ancestral character.

A homoplasy is a character that species share through convergent evolution: it is no indicator of phylogenetic relations.

An ancestral character is shared with the species ancestral to more than one group: it can lead to different groups being classified together.

A shared derived character is shared by the ancestral species and a single group: it is the only reliable guide to inferring phylogeny.