Bacidiaalbogranulosa (Ramalinaceae, lichenized Ascomycota), a new sorediate lichen from European old-growth forests.

A sterile sorediate member of the genus Bacidia s.str., B.albogranulosa, is described here as a new species. It is characterised by its very thin, pale grey thallus, white, farinose to granular soredia, the production of atranorin and the absence of ascomata and pycnidia. It grows on slightly acidic to subneutral bark of broad-leaved trees in old-growth forests in the Czech Republic, Poland, Ukraine and Russia (European part of the Caucasus). The new species is well characterised by its morphology, secondary chemistry and molecular (nrITS, mtSSU) traits. It is closely related to other atranorin-containing species in the genus, Bacidiadiffracta, B.polychroa and B.suffusa.