The scientific significance of the unicellular green algae treated in the formal genus Chlamydomonas flourishes on several fronts including use as a model system in experimental genetics, molecular biology, and gene manipulation. Modern molecular systematic studies of variability have also revealed a previously unsuspected wealth of phenotypic and genotypic diversity in the genus. Comparisons of nuclear-encoded, ribosomal RNA gene sequences revealed distinct groups of Chlamydomonas species that share more recent ancestry with other non-Chlamydomonas species, including groups of colonial Volvocales. Although these new observations conflict with the traditional taxonomy of Chlamydomonas and its allies, based largely on light-microscopy, new evolutionary interpretations of morphological variability suggest that undue influence was accorded primitive features and that ultrastructural and biochemical characters are not in conflict with the new gene data. A broader sampling of Chlamydomonas and allied species will be implemented in a new project designed to expand the molecular and morphological database for these algae and to test evolutionary hypotheses about their origin and diversification. A synthesis of modern genetic and traditional morphological approaches to the study of evolutionary patterns will serve as a key component of a taxonomic reassessment of Chlamydomonas and of other green algae as well.
