Description: Thallus crustose, epilithic, areolate. Areoles 0.2-1.2 mm diam., dispersed or gathered in small clusters, round to slighlty angular, flat to slightly convex, usually smooth, chestnut brown, generally not pruinose, with a usually darker margin and lower surface. Upper cortex paraplectenchymatous, underlain by a continuous algal layer. Apothecia 0.1-0.6 mm across, immersed or slightly protruding, usually slightly crateriform, 1-5 per squamule, with a concave, reddish brown to almost black, smooth or rarely umbonate disc, and an indistinct to slightly raised thalline margin. Epithecium pale brown; hymenium colourless, 60-110 μm tall; paraphyses 1.3-2 µm thick at base, 3-4 µm at apex; hypothecium colourless or pale straw. Asci 100-200-spored, cylindrical-clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, subcylindrical, 3-5 x 1-2 μm. Photobiont chlorococcoid. Spot tests: all negative. Chemistry: no lichen substances.
Note: a holarctic early coloniser of base- rich siliceous pebbles, roofing tiles, walls, sometimes also found on soil and lignum, also in small settlements: occasionally overgrowing other crustose lichens, with a wide altitudinal range.
Magnusson A. H. (1935) Acarosporaceae, Thelocarpaceae. - In: Rabenhorst G. L.: Kryptogamen-Flora von Deutschland, Österreich, und der Schweiz-. 2nd- IX. Die Flechten. Abt. 5- 1. Gebr. Borntraeger. Leipzig, pp. 1-318. – Public Domain
P.L. Nimis; Owner: Department of Life Sciences, University of Trieste