Description: Thallus crustose, episubstratic, areolate, grey to almost black, up to 1.1 mm thick, with glebulose, convex, 0.6-2 mm wide areoles, the marginal ones sometimes longer and indistinctly radiating. Surface of the areoles with irregular, angular, often suberect, isidia-like outgrowths. Cortex 20-40 µm thick, brown, with the subdepressa-brown pigment; algal layer more or less continuous; medulla white, I-. Apothecia rare, aspicilioid, round to irregular-elongate, 0.3-1 mm across, with a dark brown, concave to flat disc, and a thin, slightly raised thalline margin. Epithecium brown to olive-brown; hymenium colourless; paraphyses simple or sparingly branched in upper part, submoniliform; hypothecium colourless. Asci 8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, broadly ellipsoid, 12-18 x 8-10 µm. Pycnidia black, immersed, with a pale wall. Conidia thread-like, 16-20 x 0.7-1 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K+ yellow turning red (needle-like crystals), C-, KC-, P+ yellow-orange. Chemistry: norstictic acid.
Note: this silicicolous, often sterile species is known from a few localities in the Western Alps (Switzerland); to be looked for in the Italian Alps.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by isidia, or isidia-like structures (e.g. schizidia)