Towards consolidation of Gymnopilus taxonomy: the case of G. stabilis, G. sapineus, and G. penetrans

Gymnopilus stabilis (Fungi, Agaricales), a very rare species of unclear identity described from Europe, was revised using morphological data and phylogenetic affiliations derived from ITS rDNA sequences. Collections from the Czech Republic, Germany, and Russia plus reference vouchers of related or similar species were studied. Gymnopilus stabilis sequences form a moderately supported but distinct clade in a lineage containing G. swaticus and a Gymnopilus collection of unknown identity from the USA. The G. stabilis lineage is sister to the G. sapineus clade, a group of species with low divergence in ITS rDNA region. This whole, well-supported group is clearly distinct from the lineage of G. penetrans, a species with which G. stabilis has sometimes been confused. Morphological characters of a recent, well-documented Czech collection of G. stabilis are described in detail and compared with the German and Russian ones. A literature review confirms that the taxonomic concept of G. stabilis has not substantially changed over time. In order to consolidate the taxonomy and nomenclature of this enigmatic species, lectotype and epitype are designated here for G. stabilis, and key diagnostic characters are highlighted. The taxonomic concepts of G. sapineus and G. penetrans are further specified based on well-documented, sequenced reference collections. Moreover, the position of G. hybridus is briefly discussed. The identification of several GenBank entries of G. stabilis, G. sapineus, and G. penetrans is revised in order to fix species concepts in this fascinating group of wood-decaying fungi.