Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Russel L. Chapman


The phylogeny of the problematic green algal classes Prasinophyceae and Pleurastrophyceae (Chlorophyta) sensu Mattox and Stewart (1984) was inferred from ultrastructural and biochemical data, and from ribosomal RNA gene sequence data. Analysis of a data set of ultrastructural and biochemical characters (with a predominance of flagellar and cell covering features) revealed a monophyletic Pleurastrophyceae and a monophyletic Prasinophyceae. Rerooting experiments indicated that the ancestral flagellate was likely Pedinomonas-like or Mamiellales-like. The cladograms generated from the ribosomal RNA gene sequence data show that the Pleurastrophyceae is not monophyletic; however, pleurastrophycean taxa are more closely related to the Chlorophyceae than to any other class. The Ulvophyceae is the sister group to the Chlorophyceae plus Pleurastrophyceae clade. The Charophyceae and land plants represent a basal divergence relative to the Chlorophyceae plus Pleurastrophyceae plus Ulvophyceae clade. The Prasinophyceae is not a monophyletic group--some prasinophycean taxa are more closely allied to the other classes of green algae than with each other. User-defined topologies indicate that the ancestral flagellate was likely Mamiellales-like or Pyramimonadales-like. Analysis of a combined data set favored a Mamiellales-like ancestor. Despite the antiquity of the green algal lineages, randomization tests of the sequence data show a high level of phylogenetic signal and a low level of randomness in the data. A preliminary study of subgeneric relationships of the asexual green flagellate Tetraselmis was performed using sequences from polymerase chain reaction amplified internal transcribed spacer (ITS) regions 1 and 2 and the 5.8S rDNA gene. The 5.8S gene sequence was of marginal use in resolving relationships among the subgenera. The ITS regions were variable enough to resolve relationships among the three subgenera.