XVI International Botanical Congess

Within the loculoascomycetes, the ordinal separation of the Pleosporales and Melanommatales has mainly been based on their hamathecial morphology, the former having cellular pseudoparaphyses and the latter trabeculate pseudoparaphyses. Whether this differentiation on the basis of the pseudoparaphysis type reflects true phylogeny has often been questioned. We have assessed the phylogenetic validity of the separation of these two orders by analysis of the 18S subunit of the ribosomal RNA genes. Partial sequences of this gene were obtained from 24 Pleosporales taxa and 9 from the Melanommatales. As outgroups, 8 other loculoascomycetes from the Patelleriales, Chaetopthyriales, and Dothideales, as well as 3 unitunicate pyrenomycetes and a basal ascomycete were used. The sequences were aligned and subjected to phylogenetic analysis. Results are presented and discussed.