Microbotryum, Kriegeria and the Changing Paradigm in Basidiomycete Classification

Until recently the sedge parasite Kriegeria eriophori has never been satisfactorily classified above the genus level. Its classification has been problematic in that a number of characters at the gross micromorphological and ultrastructural levels appeared to be autapomorphic. The use of nucleotide sequence data has proven to be a powerful means of addressing difficult systematic problems in which standard morphological approaches have failed to provide sufficient information. During this study, some of these ultrastructural characters were discovered to be synapomorphies for a group containing K. eriophori and Microbotryum, violaceum, a urediniomycete smut species. Ribosomal RNA gene sequences and nucleus-associated ultrastructural characters were analysed separately and combined. These characters serve to define the new subclass Microbotryomycetidae. Inclusion of the sequences in the analysis provided an independent data set by which the ultrastructural character states were polarized. Gross micromorphological characters proved to be homoplasious, and of less utility in determining phylogenetic groups than were ultrastructural and nucleotide characters. Cladistic analysis of ultrastructural and biochemical characters provides a powerful means of identifying monophyletic groups, the prerequisite for creating a phylogenetic classification. A phylogenetic diagnosis is provided for the Microbotryomycetidae, which deviates from the pattern used in typical diagnoses.