Description: Thallus crustose, endosubstratic, to thinly episubstratic and areolate, whitish, sometimes delimited by a very thin pale prothallus, forming orbicular patches to 4 cm in diam. Areoles sparse, discrete or contiguous, becoming more or less convex, usually esorediate. Medulla white, I-. Soralia bursting through the cell-layers of the substrate, often delimited by a thin, lacerate rim of bark or wood cells, pale green to bluish green, but frequently darkened and brownish to blackish, orbicular to ellipsoid-elongate, flat to crateriform, to 0.4 mm in diam., bearing farinose, to 30 µm wide soredia which are strongly inspersed with crystals dissolving in K. Apothecia rare, lecideine, black, 0.2-0.5 mm across, initially more or less immersed, then sessile, with a concave to rarely flat disc, and a thin, usually persistent proper margin. Proper exciple dispersa-type, the inner hyphae distinct, pigmented, prosoplectenchymatous, the outer hyphae with short, angular, distinctly swollen cells more or less carbonized with a brown pigment; epithecium olive-brown, N-; hymenium colourless, to 120 µm high, strongly inspersed with oil droplets; paraphyses simple or sparingly branched, 1.5-2 µm thick in lower part, apically swollen to 4-5 µm, with a brown pigment cap; hypothecium deep reddish brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 1(-3)-septate, soon brown, narrowly ellipsoid, usually not constricted at septum, with pointed and often paler ends, sometimes slightly curved, 18-28 x 7.5-12.5 µm, Callispora-type. Photobionr chlorococcoid. Spot tests: thallus K+ yellow, C-, KC-, P- or P+ yellow, UV-. Chemistry: atranorin, placodiolic acid.
Note: a usually sterile species with bluish-greenish, round to elongated, and flat to concave soralia reacting K- in squash preparations; usually found on periodically dry wood of logs and old fences in upland areas; certainly more widespread in the Alps, and locally rather common.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)