A revision of the Rostania occultata (Collemataceae) complex in Fennoscandia

Abstract The Rostania occultata species complex (‘ Collema occultatum s. lat.’) is revised in Fennoscandia and found to consist of four species, all epiphytes on deciduous trees: effusa A. Košuth., M. Westb. & Wedin sp. nov., R. (Bagl.) Otálora et al ., pallida nov. populina (Th. Fr.) comb. are newly described from humid habitats old-growth boreal coniferous forests, usually with a mixture trees, similar areas the subalpine birch-dominated forests Fennoscandia. characterized by apothecia red-brown apothecium discs an excipulum thallinum simple pseudocortex cubic oblong, muriform spores. has whitish pale yellowish distinct cellular pseudocortex, ellipsoid, mature spores that often constricted at centre. A lectotype designated for quadratum J. Lahm ex Körb. new combination introduced recognized until now as variety var. Perlmutter Rivas Plata. key six str. included.