Reciprocal Monophyly

Lineages sampled from two groups, \(A\) and \(B\), are reciprocally monophyletic if the lineages from group \(A\) have a shared common ancestor that is more recent than the most recent common ancestor any of the group \(A\) lineages has with a lineage of \(B\), and if the lineages from group \(B\) have a shared common ancestor that is more recent than the most recent common ancestor any of them has with a lineage of \(A\). Reciprocal monophyly is a criterion for identifying pairs of groups as genealogically distinct, and it is used for this purpose in a variety of applications in studies of phylogenetics, population genetics, speciation, and conservation genetics.