Description: Thallus crustose, endosubstratic or thinly episubstratic and rimose-areolate, white to dirty grey, sometimes with a brownish tinge. Areoles 0.3-0.6 mm wide, separated by narrow cracks. Thallus pseudoparenchymatous throughout, the outermost layer forming a thin, colourless pseudocortex of spherical cells; algal cells more or less distinctly arranged in vertical columns separated by strands of mycobiont cells. Perithecia black, 0.5-0.8 mm across, hemispherical to flattened, formed singly or in groups, the ostiolar region often depressed, the outer surface coarsely uneven in upper part, sometimes covered by a very thin thalline layer at the base. Involucrellum reaching down to the thallus, diverging towards the base, gradually thickened toward the base (120-140 µm thick), strongly carbonized; exciple 22-31 µm thick, brown, paraplectenchymatous; hamathecium of thin, c. 1.2 µm wide, sparingly branched pseudoparaphyses, interascal filaments absent; hymenial gel I+red, K/I+blue. Asci 8-spored, clavate, without apical thickening when mature. Ascospores muriform, at first hyaline but soon turning brown, ellipsoid, often slightly asymmetric and curved, 27-39 x 16-20 µm, the surface minutely punctate. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on siliceous to somewhat calcareous, wet rocks in open situations, often on slate, usually along rivers or by lakeshores or on pebbles at least intermittently flushed with running water, near or above treeline.