THE PLEURASTROPHYCEAE AND MICROMONADOPHYCEAE - A CLADISTIC-ANALYSIS OF NUCLEAR RIBOSOMAL-RNA SEQUENCE DATA

Partial sequences from the nuclear-encoded 18S and 26S ribosomal RNA molecules from representatives of the five classes of Chlorophyta sensu Mattox and Stewart (1984) were analyzed cladistically in a study of the phylogenetic relationships among the Micromonadophyceae, Pleurastrophyceae, and other green algae. The sequence data indicate that the Micromonadophyceae (= Prasino-phyceae) is not monophyletic but comprises at least three lineages occupying a basal position among the green algae. Though the Pleurastrophyceae and the Ulvophyceae both possess counter-clockwise basal body orientations, the sequence data indicate that the Pleurastrophyceae is the sister group to the Chlorophyceae. The molecular data alone do not resolve the monophyly of the Pleurastrophyceae or the Ulvophyceae; however, a combined data set of molecular and non-molecular characters support a monophyletic Pleurastrophyceae. Analyses with user-defined tree topologies and the bootstrap method of character resampling indicate that the relationships shown in the most parsimonious cladograms are well supported by the character data.