Three species of Hypomyces growing on basidiomata of Stereaceae.

Of the eight species of Hypomyces that occur on basidiomata of Stereum species, only H. sympodiophorus grows exclusively on members of this genus. Morphologically similar fungi were found on species of Xylobolus, a genus closely related to Stereum. These are described as two new species of Hypomyces: H. thailandicus, collected on Xylobolus cf. illudens in Thailand; and H. xyloboli, on X. frustulatus and X. subpileatus in the eastern United States. These three species are unusual in Hypomyces because of their almost indistinguishable anamorphs. In parsimony analysis of LSU nuclear rDNA sequences, the three species growing only on Stereaceae do not form a monophyletic group but their constrained monophyly is not rejected either. A morphologically similar anamorphic species, Sibirina gamsii, included in the study, is transferred to the genus Cladobotryum.