Disentangling the taxonomy of Octospora meslinii (Pezizales), a bryophilous ascomycete on Grimmia pulvinata.

The bryophilous ascomycete Octospora meslinii is a rarely reported species growing exclusively in cushions of the saxicolous moss Grimmia pulvinata. The taxon has been misunderstood in the past and hitherto reliably only reported from France and Germany. Many recent collections from Hungary have made it possible to get a better understanding of O. meslinii, which is comprehensively described and illustrated in this paper. Because of the lack of original material, we designate an illustration in the protologue as the lectotype and one of the recent collections as the epitype of this fungus. Octospora meslinii is compared with other species of Octospora growing in the same type of habitat or having similar ascospores. The most closely related species to O. meslinii is O. pseudoampezzana. Both share apothecia with blackish pigmentation, a unique feature compared to bryophilous Pezizales as a whole, ellipsoid ascospores ornamented with isolated warts, moss hosts in the family Grimmiaceae, and the infection inducing galls on the rhizoids. A phylogenetic analysis using the EF1 , LSU and SSU rDNA loci confirms our morphological findings showing that O. meslinii forms a monophyletic clade with O. pseudoampezzana, whereas other species with which O. meslinii was confused in the past, e.g. O. similis, are related only distantly.