Biatoropsis usnearum Räsänen, and Other Heterobasidiomycetes on Usnea

Abstract

The pinkish galls on Usnea, often called Biatoropsis usnearum are shown to represent basidiomata of a previously unrecognized genus of heterobasidiomycetes with transversely septate basidia, to which the generic name Biatoropsis can be applied. The new genus is tentatively included in the Platygloeales. The hyphomycetous anamorph strongly resembles the genus Hormomyces. Biatoropsis usnearum is very frequent and widely distributed on Usnea, but has also been collected on Protousnea; the galls have been found parasitized by Abrothallus usneae and three species of Lichenoconium. Two other heterobasidiomycetes growing on Usnea are described: Tremella santessonii Diederich sp. nov. from Africa has transversally 1- septate basidia; T. stevensiana Diederich sp. nov. from Australia has longitudinally 1-3-septate basidia and a type of hyphomycetous anamorph poorly known in other species of Tremellales. Several other Tremella–like or gall-forming fungi on Usnea are briefly discussed.