PRASINOPHYTES FORM INDEPENDENT LINEAGES WITHIN THE CHLOROPHYTA - EVIDENCE FROM RIBOSOMAL-RNA SEQUENCE COMPARISON

Complete nuclear-encoded small-subunit ribosomal RNA (rRNA) sequences were determined from Nephroselmis olivacea Stein, Pseudoscourfieldia m arina (Throndsen) Manton, Scherffelia dubia (Perty) Pascher, and Tetra selmis striata Butcher (Chlorophyta) to investigate the evolutionary p osition of these scaly green flagellates. Results of neighbor-joining and maximum parsimony phylogenetic analyses demonstrate at least two i ndependent prasinophyte lineages defined by N. olivacea/P. marina and S. dubia/T. striata, which together with the Chlorophyceae, Pleurastro phyceae, and Ulvophyceae form a monophyletic group. Within this assemb lage, N. olivacea and P. marina represent an early-diverging lineage t hat is evolutionarily distinct from the later-diverging S. dubia/T. st riata clade. The branch point of the S. dubia/T. striata clade precede s the near-simultaneous radiation of the Chlorophyceae, Ulvophyceae, a nd Microthamniales. Though interrelationships between these three latt er groups of algae are not resolved, the phylogenetic analyses demonst rate that the Prasinophyceae (sensu Moestrup and Throndsen) and the Pl eurastrophyceae (sensu Mattox and Stewart) are not monophyletic classe s.