Phylogenetic evidence places the coralloid jelly fungus Tremellodendropsis tuberosa (Tremellodendropsidales) among early diverging Agaricomycetes

Abstract

We explored the phylogenetic relationships of Tremellodendropsis tuberosa from western North America. The species has tough, coralloid fruiting bodies that emerge from a basal tuber, as well as unusual, partially septate basidia, large elliptical spores, and regular clamp connections. It has been classified variously in Auriculariales, Tremellales, and in its own order, Tremellodendropsidiales. To evaluate support for these alternatives, we extracted DNA from four specimens and sequenced ∼5000 bp from the ribosomal large subunit, small subunit and internal transcribed spacer region from each. We aligned sequences from T. tuberosa with sequences from GenBank that represented 31 Basidiomycota orders and then analyzed the individual and concatenated sequence regions using Bayesian and maximum likelihood approaches. Analyses agreed that T. tuberosa is an early diverging member of Agaricomycetes, but did not provide unequivocal support for its sister group relationships within the class. From the concatenated alignment, after removal of poorly aligned sites using Gblocks, T. tuberosa appeared as the sister group to a clade encompassing four orders, three of them from Phallomycetidae. This relationship had a Bayesian posterior probability of 1.0 and appeared, although without bootstrap support, in maximum likelihood trees. Tree topology tests ruled out placing T. tuberosa within the Auriculariales. We accept that T. tuberosa should be placed in its own order, the Tremellodendropsidales, and not in Auriculariales or Tremellales. As a taxon that diverged early from other Basidiomycota clades, T. tuberosa should be included in further studies of phylogeny and character evolution in Agaricomycetes.