PHYLOGENETIC-RELATIONSHIPS WITHIN THE COLONIAL VOLVOCALES (CHLOROPHYTA) INFERRED FROM CLADISTIC-ANALYSIS BASED ON MORPHOLOGICAL DATA

A cladistic analysis was used to deduce the phylogenetic relationships within the colonial Volvocales. Forty-one pairs of characters related to gross morphology and ultrastructure of vegetative colonies as well as asexual and sexual reproduction were analyzed based on parsimony, using the PAUP 3.0 computer program, for 25 species belonging to nine volvocacean and goniacean genera of the colonial Volvocales. Chlamydom onas reinhardtii Dangeard was the outgroup. The strict consensus tree indicated the presence of two monophyletic groups, one composed of all the volvocacean species analyzed in this study and the other containi ng the goniacean species except for the four-celled species Gonium soc iale (Dujardin) Warming. In addition, these two groups constitute a la rge monophyletic group, to which G. sociale is a sister group. A new c ombination Tetrabaena socialis (Dujardin) Nozaki et Itoh and a new fam ily Tetrabaenaceae Nozaki et Itoh are thus proposed for G. sociale. In addition, the analysis suggests that the volvocacean genera Eudorina and Pleodorina are paraphyletic groups, respectively, and that the mon otypic genus Yamagishiella has no autapomorphic characters and represe nts primitive features of the anisogamous and oogamous genera of the V olvocaceae. Phylogenetic relationships within the Volvocaceae and the Goniaceae, as well as the various modes of sexual reproduction exhibit ed by these organisms, are discussed on the basis of the analysis.