Caloplaca obscurella (Körb.) Th. Fr.
Thallus crustose, initially thin, more or less thick according to age and substratum, almost smooth to uneven, rough to areolate, greyish to pale to dark grey, covered on almost all the surface with granular vesicles, 0,1-0,3 mm diam., that open and give rise to soralia white to grey, usually concave and crater-like, and containing grey-green to greyish soredia. Apothecia rather rare, in small number, scattered, rounded, to 0.5-0.8 mm diam., disc convex, dark brown, concolourous margin soon excluded. Ascospores ellipsoid, polarilocular, septum 4-6 µm wide, 10-13 x 6-8 µm. Photobiont : trebouxioide.. Thallus and apothecia K-. Corticolous, on bark at the base of fruit trees in old orchards, also on Populus, Salix.*