THE PHYLOGENY OF THE HYPHOCHYTRIOMYCOTA AS DEDUCED FROM RIBOSOMAL-RNASEQUENCES OF HYPHOCHYTRIUM CATENOIDES

Based on biochemical and ultrastructural data, hyphochytriomycetes are believed to share an ancestor with oomycetes and heterokont algae. In order to study the phylogeny of the hyphochytriomycetes, we determine d both the small- and large-subunit ribosomal RNA sequence of Hyphochy trium catenoides. Phylogenetic trees were constructed using the neighb or-joining and maximum-parsimony method and include representatives of Chlorobionta, Fungi, Metazoa, Alveolata, and all known Heterokonta. O ur main conclusion is that the hyphochytriomycetes form a monophyletic group with the oomycetes and heterokont algae and that they are proba bly the closest relatives of the oomycetes. However, the order of dive rgence between the various heterokont algal phyla and the oomycete-hyp hochytriomycete cluster remains uncertain.