Phylogeny of wall-less green flagellates inferred from 18SrDNA sequence data.

To elucidate the phylogeny of the Dunaliellales sensu Ettl, the taxon often thought to be intermediate between primitive green flagellates such as the parasinophytes and the advanced chlorophycean algae, the sequences of the nuclear-encoded small subunit ribosomal RNA gene (18SrDNA) were determined and analyzed for five green algae, including three dunaliellalean algae. Phylogenetic trees based on 18SrDNA suggest that OltmannsielIopsis viridis (Hargraves et Steele) Cnhara et lnouye represents an early divergence in the Ulvophyceae/Trebouxio- phyceae/Chlorophyceae dade and has no close relationship to any other green algae, as also suggested from ultrastructural characters. We propose Oltmannsietlopsidales ord. nov. for this genus. Hafniomonas and Polytomefla are included in the dade which is characterized by clockwise basal bodies (OW group). The 18SrDNA trees suggest that multiple losses of the cell wall of the flagellate cell occurred in the CW group, and that the Dunaliellales sensu EttI has a polyphyletic nature. This study also suggests that Planophila terrestris Groover et Hofstetter (Chaetopeltidales) and Chactophora incrassate (Hudson) Hazen (Chaetophorales) are distinct lineages in the Chlorophyceae. [ABSTRACT FROM AUTHOR]