This study will use nuclear and mitochondrial rDNA sequence information to assess phylogenetic relatedness of organisms derived from the various ancestral groups of present day Oomycota. The utility of these molecules for studying relationships will be evaluated at different taxonomic levels. Inferences will be derived concerning which groups are monophyletic relative to ancestors of the Chromista (Cavalier- Smith 1986-includes Chrysophyceae, Xanthophyceae, Bacilliarophyceae etc.) and should, therefore, be included in a revised Oomycota. Phylogenetic schemes based on molecular data will be used to test those based on other existing non-molecular characters. Preliminary molecular analyses and those based on zoospore ultrastructural characters have resulted in the same phylogenetic relationships among the groups in common and this approach can provide the truest understanding of their phylogenetic relationships. The relationships of these groups to other protist lineages will provide a pivotal framework for examining and predicting every aspect of their biology and will be highly useful in selecting a suite of appropriate characters for further phylogenetic investigations in this and related groups.
