Description: Thallus squamulose, pale greyish brown to brownish, dull, rarely faintly pruinose at margin. Squamules 1-3 mm broad, 0.15-0.4 mm thick, rounded to crenulate, concave to convex, but usually flattened, smooth, densely imbricate, forming 2-4 cm wide cushions. Lower surface whitish to yellowish white or very pale brown, attached by 4-5 μm thick, pale rhizohyphae which are usually present only at the base of squamules. Upper cortex paraplectenchymatous 20-40 μm thick, of 4-13 μm wide, angular cells; medulla of globose cells; lower cortex not clearly delimited from the medulla. Perithecia rather rare, laminal, subglobose to pyriform, immersed, to 0.35 mm broad, without involucrellum. Exciple initially pale, then brown, finally dark brown to black; paraphyses absent, substituted by periphyses. Asci 8-spored, unitunicate, clavate, not or only slightly thickened at apex, without ocular chamber, the wall I-. Ascospores 1-celled, hyaline, biseriately arranged in the asci, narrowly ellipsoid, thin-walled, (11-)12-16(-17) x 5-7 μm. Pycnidia dark, immersed. Conidia subcylindrical, 4-5 x c. 1 μm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: in fissures of hard calcareous rocks and amongst mosses, especially limestone, in rather sheltered situations, at low elevations.