Description: Thallus crustose, episubstratic, starting the life-cycle on other silicicolous lichens, up to 0.8 mm thick and up to 4 cm wide, rimose-areolate, dark brown to almost black, minutely isidioid or granular-sorediate, the granules (20-)30-40(-50) μm in diam, the areoles flat to slightly convex, irregular in outline, 0.4-0.5 mm wide. Apothecia not always present, lecideine, black, 0.3-0.8(-1.2) mm across, broadly adnate, with a flat to convex disc and a thin, raised proper margin. Proper exciple thin, 20-45 μm wide laterally, dark brown or olive brown throughout; epithecium dark brown; hymenium colourless, (40-)60-75 μm high; paraphyses richly branched and anastomosing, the apical cells not strongly capitate; hypothecium pale to dark brown, 60-130 μm high. Asci 8-spored, broadly clavate, with a K/I+ blue tholus with a funnel-shaped central unstained region, and a small, obconical K/I+ blue dome. Ascospores 1-celled, hyaline, ellipsoid, (10-)12-16(-20) x (5.5-)6-9(-10) μm. Photobiont chlorococcoid, the cells 6-12 μm wide. Spot tests: thallus, especially medulla, K-, C+ pink or rarely C-, KC+ pink or rarely KC-, P-. Chemistry: thallus with variable amounts of gyrophoric and rarely norstictic acids.
Note: this silicicolous species is able to invade several crustose lichens pertaining to different lineages, most often of Rhizocarpon-species; it certainly occurs also in the Alps, but was largely overlooked.