RIBOSOMAL-RNA GENE-SEQUENCES - ANALYSIS AND SIGNIFICANCE IN THE PHYLOGENY AND TAXONOMY OF GREEN-ALGAE

The morphologically diverse green algae (Chlorophyta) include distinct, ancient lineages for which phylogenetic inference from morphological, ultrastructural, and biochemical characters has led to conflicting hypotheses. Cladistic analysis of ribosomal RNA (rRNA) sequences has indicated that (1) some traditional genera are not monophyletic (natural) and taxonomic revisions are needed; (2) ultrastructural characters associated with mitosis and cytokinesis appear to be better indicators of phylogeny than flagellar characters for some taxa; (3) the unusual, subaerial Trentepohliales of incertae sedis appear to be most closely related to the marine siphonaceous green algae; and (4) ancient groups (e.g., Charophyceae and Dasycladales) are resolved. With polymerase chain reaction (PCR) amplification and sequencing of highly variable rDNA gene spacer regions, closely related taxa or populations of one species can be compared and biogeographic studies based on rRNA are feasible. Sequence comparisons for ATPase genes may provide an additional perspective on ancient divergences and will thus complement rRNA studies.