Thallus to 40 mm diam, effuse, areolate to irregularly cracked areolate, or sometimes continuous, areoles initially consisting as disperse squamules, 0.1-0.3(-0.5) mm diam, 100-150 µm tall, rounded, flat to somewhat verrucose, slightly lobulate with a rounded outline, expanding to 1-1.5 mm diam and ca 300 µm tall, uneven, densely aggregated and often overlapping and incised, subunits sometimes nearly isidia-like, 100-250 µm diam. Upper surface of areoles plane to slightly verrucose, greenish grey to pale brown, matt, epinecral layer lacking or thin, to 5(-10) µm thick, hyaline, cells mostly visible. Cortex 5-20 µm thick, sometimes with a few algae, upper part pale brown; cells roundish to angular, 5-6 x 4-5 µm in size. Medulla with chlorococcoid photobiont, with subglobose cells 5-9 x 3-6 µm in size. Thallus below algal layer becoming discontinuous, merging into an endolithic hypothallus. Hypothallus weakly developed, mostly lacking, in calcareous rock to 300 µm deep. Medulla below perithecia with clusters of crystals to 15 µm diam. Rhizoidal hyphae rare, hyaline, 2-4 µm diam.
Anamorph: conidiomata pycnidial, inconspicuous and only occasionally present, ca 100 µm diam. Conidia 3.8-4.4 x 0.9-1.1 µm, short-bacilliform with rounded ends, sometimes slightly curved.
Teleomorph: ascomata perithecia, mostly half-immersed, subglobose, black, numerous, evenly distributed or gathered in clusters of up to 5, half to almost completely laterally covered by the squamules, sometimes located at the edge of or between the squamules. Involucrellum clearly visible, often covered with a thin pale layer of thallus, 370-900 µm diam, 50-70 µm thick, black, reaching the base of the perithecia, ± contiguous with the excipulum or slightly spreading, at the inner side somewhat brownish transparent. Excipulum ca 260-360 µm tall and 240-350 diam, with a relatively short neck, the ostiole appearing whitish to brown. Wall of excipulum laterally 12 - 25 µm wide, pale brownish below in older perithecia. Periphyses simple to sometimes branched, strongly coherent, septate. Interascal tissue absent. Asci 75-90 x 20-30 clavate, 75-90 x 20-30 µm, I- and KI-, 8-spored. Ascospores biseriately arranged, 23-28 x 8-13 (-15) µm, hyaline, aseptate, ellipsoidal to ovoid, thin-walled, smooth.