Five new species in Piloderma (Atheliales, Basidiomycota) and epitypification of P. byssinum

Piloderma constitutes a small genus of soft, corticioid, ectomycorrhizal, widely distributed and mostly very common species. Microscopically, its members have traditionally been recognised by their simple-septate hyphae and by their small, thick-walled, colourless to pale yellow spores. We describe five new species from northern Europe based on molecular and morphological data: P. frondosum sp. nov., P. fugax sp. nov., P. lamprolithum sp. nov., P. luminosum sp. nov. and P. mirabile sp. nov. All the new species, except P. luminosum seem to be more or less rare. Piloderma fugax has a strong preference for old-growth forest - a lifestyle seemingly deviating from the rest of the genus. Piloderma mirabile is a sister species to P. sphaerosporum and the first known species with clamped hyphae. Piloderma lamprolithum is closely related to P. exiguum and distinguished by its large encrusting crystals. Piloderma luminosum is very closely related to, and morphologically semicryptic with, P. byssinum. To clarify its distinction from P. byssinum, an epitype is designated for the latter. Piloderma frondosum also belongs to the P. byssinum cluster and is distinguished by its association to broadleaved trees. An updated key to all Piloderma species is provided.