Description: Thallus crustose, episubstratic, 1.5-3(-5) mm thick in central parts, forming small patches, sometimes delimited by a grey prothallus, finely rimose-areolate, the areoles contiguous, flat to slightly convex, greyish white to pale bluish grey. Cortex 10-17 µm thick; medulla thick, white, I+ deep blue. Apothecia lecideine, black, mostly developed between the areoles, usually clustered, 0.3-1.8 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; epithecium olive-brown, grey or green-black, 10-15 µm high; hymenium colourless or pale green, 40-75 µm high, I+ blue; paraphyses simple or rarely branched, usually not anastomosing, 1.8-2.7 µm thick at mid-level, the apical cell 3.5-6 µm wide; hypothecium colourless to very pale green or yellowish brown. Asci 8-spored, clavate, Lecidea-type. Ascospores 1-celled, hyaline, ellipsoid to broadly ellipsoid, 8-11 x 4.5-6 µm, not halonate, rather thick-walled. Pycnidia semi-immersed, black, the ostiolar region often elongate and almost lirelliform. Conidia bacilliform, 7-19 x 1-1.5 µm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: confluentic acid (major).
Note: on calciferous siliceous rocks, dolomite, superficially decalcified, hard limestone rocks near and above treeline, starting the life-cycle on other crustose lichens, especially Aspicilia spp.