Phylogenetic relationships, species concepts and morphological evolution of the coprinoid mushroom genus Parasola were studied. A combined dataset of nuclear ribosomal ITS and LSU sequences was used to infer phylogenetic relationships of Parasola species and several outgroup taxa. Clades recovered in the phylogenetic analyses corresponded well to morphologically discernable species, although in the case of P. leiocephala, P. lilatincta and P. plicatilis amended concepts proved necessary. Parasola galericuliformis and P. hemerobia are shown to be synonymous with P. leiocephala and P. plicatilis, respectively. By mapping morphological characters on the phylogeny, it is shown that the emergence of deliquescent Parasola taxa was accompanied by the development of pleurocystidia, brachybasidia and a plicate pileus. Spore shape and the position of the germ pore on the spores showed definite evolutionary trends within the group: from ellipsoid the former becomes more voluminous and heart-shaped, the latter evolves from central to eccentric in taxa referred to as 'crown' Parasola species. The results are discussed and compared to other Coprinus s.l. and Psathyrella taxa. Homoplasy and phylogenetic significance of various morphological characters, as well as indels in ITS and LSU sequences, are also evaluated.
Keywords: Agaricales; Coprinus section Glabri; Psathyrella; deliquescence; gap coding; morphological traits; species concept.