Phylogenetic diversity is a measure of biodiversity which incorporates
phylogenetic difference between species. It is defined and calculated as "the sum of the lengths of all those branches that are members of the corresponding minimum spanning path", in which 'branch' is a segment of a
cladogram, and the minimum spanning path is the minimum distance between the two nodes. This definition is distinct from earlier measures which attempted to incorporate phylogenetic diversity into conservation planning, such as the measure of 'taxic diversity' introduced by Vane-Wright, Humphries, and William.