Relative Symmetry of Cladograms and Phenograms: An Experimental Study

Abstract

After long experience of computing both cladograms and phenograms, I have a strong impression that cladograms are gen? erally less symmetrical than are pheno? grams, a view that seems widely shared among numerical taxonomists. I did once comment briefly on the matter (Colless, 1982) and sought to illustrate the point by devising an index of symmetry that I ap? plied to several dendrograms of both kinds. Since then, several authors have shown in? terest in the topic, most recently Heard (1992> and Rogers (1993) (these authors give other relevant references). The index, which I did not name, has been variously chris? tened and rechristened since: I here call it