Description: Thallus crustose, episubstratic, whitish, forming 1-4 mm wide, rounded to irregular, flat to slightly convex islands on the thalli of other crustose lichens (Aspicilia-species). Cortex with an epinecral layer; medulla, white, I+ deep blue at least in lower part. Apothecia lecideine/biatorine, black, semi-immersed to appressed, rounded to angular in outline, 0.3-0.8 mm across, with a black, flat to slightly convex, epruinose or weakly pruinose disc, and a thin, often soon excluded proper margin. Proper exciple poorly developed, with a brownish rim, colourless within, 25-40 µm wide in upper part; epithecium olive-brown to green-black; hymenium colourless, 40-60 µm high, I+ blue; paraphyses coherent, simple or rarely branched in upper part, usually not anastomosing, the apical cells 4-5 µm wide; hypothecium colourless to very pale brown, I+ blue. Asci 8-spored, narrowly clavate, thick-walled, with a K/I+ pale blue tholus and a strongly amyloid, thin apical cushion, surrounded by a I+ blue outer layer, Lecidea-type. Ascospores 1-celled, hyaline, ellipsoid to broadly ellipsoid, 8.5-11 x 5-6 µm, not halonate, rather thick-walled. Pycnidia developed on sterile, smaller (1-3 mm wide) thalli, semi-immersed, black, the ostiolar region at first punctiform, then expanded. Conidia bacilliform, straight to slightly curved, (7-)10-12(-14) x 1-1.5(-2) µm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: confluentic acid syndrome.
Note: an arctic-alpine, bipolar silicicolous species with a peculiar ecology (Hertel 2006), always growing on Aspicilia species near or above treeline; related to L. tessellata.