Applied to apomorphic features that are possessed by two or more taxa in common (i.e. the features are shared, derived). If the two groups share a character state that is not the primitive one, it is plausible that they are related in an evolutionary sense, and only synapomorphic character states can be used as evidence that taxa are related. Phylogenetic trees are built up by discovering groups united by synapomorphies.
Subjects: Biological Sciences.