Toward a phylogenetic systematics of the basidiomycota: Integrating yeasts and filamentous basidiomycetes using 18S RRNA gene sequences.

A considerable database of sequences of the 18S rRNA gene of basidiomycetes exists. Analyses of these data have usually consisted of either yeast taxa or filamentous taxa, while few have attempted an integrated picture of basidiomycete phylogeny including both. This study made use of the partial 18S rRNA gene sequences available for a number of basidiomycetous yeasts to integrate these species into a general basidiomycete phylogenetic framework developed from analysis of more nearly complete 18S gene sequences. The analysis was performed in two parts. In the first phase, species were added sequentially into a parsimony analysis consisting of the species from which the general basidiomycete phylogenetic framework was derived. After determining upon which of the major lineages a test species resided, the second phase of analysis was performed. The second phase of analysis used both parsimony and neighbor joining methods to estimate the phylogenetic placement of the test species within a major lineage. The species tested were divided between the subclass Tremellomycetidae (tremellaceous yeasts), and the class Urediniomycetes emend. ('ustilaginaceous' yeasts). None of the species tested grouped with representatives of the Ustilaginales s.s., Ustilago hordei and Ustilago maydis.

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