Patrocladistic classification

Cladistic approaches to classification have become routine in plant systematics. Many workers now accept the following rules: (1) only synapomorphies are important for determining branching patterns (cladograms); (2) only holophyletic groups are acceptable; (3) classifications must be based directly upon these topological patterns; and (4) sister groups should have the same rank. Despite many positive aspects of cladistics, there remain several problems. Perhaps the most critical difficulty, and that which has led to the most discussion, is how to deal with character state evolution within lineages (i.e., the patristic divergence). This relates directly to the issue of recognition of paraphyletic groups. We present a new method for directly combining patristic and cladistic distances in an explicitly generated branching diagram (patrocladogram). This diagram can serve for classification using cladistic rules, because the patristic dimension has already been taken into account in the analysis. Controversial problems associated with paraphyletic groups vanish. Three examples are provided from plant groups at different levels of the taxonomic hierarchy with morphological and molecular data to suggest efficacy of the method.