Delimitation of an almost forgotten species Spongipellis litschaueri (Polyporales, Basidiomycota) and its taxonomic position within the genus

Spongipellis litschaueri, described in 1931 from Austria, is often synonymised with S. delectans in current literature. Morphological and molecular approaches were applied to revise the taxonomic position of this species. The basidiospore dimensions and DNA sequences confirmed differences between S. delectans and S. litschaueri, thus the latter should be kept as a distinct species. However, the relationship between S. litschaueri and its North American kin S. unicolor is complex. Although most of the examined specimens of S. unicolor differ significantly from S. litschaueri in morphological and molecular characters, one American isolate showed markedly high DNA sequence similarity to the European species. Moreover, specimens of S. unicolor from the more or less western USA have larger basidiospores than the others and the respective values are similar to S. litschaueri. Thereby, S. unicolor may split in two taxa where one is closely related to S. litschaueri. Additionally, DNA sequences of a large subunit of the nuclear ribosomal RNA gene were analysed to elucidate the position of Spongipellis within the Polyporales. The results revealed unexpected polyphyly when the generic type S. spumeus fell into a separate lineage from S. delectans, S. litschaueri, S. pachyodon, and S. unicolor. In addition, Tyromyces fissilis occasionally kept in Spongipellis is not related to any species of the genus nor to Tyromyces chioneus, the generic type of Tyromyces. An identification key of European Spongipellis species is provided.