A phylogenetic evaluation of the tribe Leucopaxilleae: polyphyly, the LPD grade, and novel taxa from the Southern Appalachians

Toyota Auditorium, Howard H. Baker Jr. Center for Public Policy

The tribe Leucopaxilleae Singer comprises eight genera that have been placed at various taxonomic ranks. Phylogenetic analysis of a four-gene region supermatrix (nuclear rRNA regions, rpb2) shows the tribe to be highly polyphyletic, with genera distributed in the Tricholomatoid, Marasmioid, Hygrophoroid and Pluteoid clades. Leucopaxillus, Porpoloma and Dennisiomyces, occur in the Tricholomatoid clade. Dennisiomyces, primarily a neotropical genus, has not been previously considered part of the Leucopaxilleae. We present preliminary data that suggest Dennisiomyces is closely related to Leucopaxillus and Porpoloma forming the 'LPD' grade (or clade) from which the ectomycorrhizal (ECM) genus Tricholoma appears to be derived. These results also suggest that Leucopaxillus and Porpoloma are polyphyletic. Additionally, three unknown species that form a clade nested in the 'LPD' grade have been collected recently from the Southern Appalachians of the southeast United States. They are distinguished from other species in the grade by possession of distinct cheilocystidia and pleurocystidia, presence of clamp connections, and inamyloid smooth spores. At present, we are unable to ascribe any known genus to this apparent endemic group.