Parsimony and Paraphyly

Abstract

Phylogenetic analysis may be described as the attempt to discover nested monophyletic groups. ‘Monophyly’ here is used in the sense of Hennig (1966) and is equivalent to Ashlock’s (1971) ‘holophyletic’ group. The characterization of such a group is clear; it is distinguished by a set of non-convergent derived character states (synapomorphies). A group that is not monophyletic may be further characterized by the use of two other terms, ‘paraphyly’ and ‘polyphyly’. However, these terms have been applied to a range of different concepts, with the result that a confusing array of different definitions exists for each (see Holmes 1980 for a recent review). Certainly clarification of these definitions is important as the terms are used by both ‘cladists’ and evolutionary taxonomists and are useful in the evaluation of these different approaches to classification.