Pluteus ursulus, a new species of sect. Celluloderma from Russia

A new Pluteus species, P. ursulus, from the Russian Far East was described based on morpho­logical and molecular characters. Pluteus ursulus is characterized by small basidiomata with dark brown squamulose pileus and squamulose stipe, pigmented lamellae edges, fusiform or utriform pleurocystidia, clavate or lanceolate cheilocystidia with brown content, basidiospores highly variable in size, (4.5)5.3‒6.8(8.2) × 4.2‒5.5(6.8) µm, lack clamp connections in all tissues, and growing on deciduous wood. The phylogenetic placement of the newly described species in Pluteus sect. Celluloderma (/podospileus clade) was confirmed using DNA data (nuclear ribosomal internal transcribed spacer—ITS and translation-elongation factor 1-alpha—TEF1). Detailed morphological description, field photographs, and comparison of the new species with other morphologically and phylogenetically closely related species are provided.