Description: Thallus crustose, episubstratic, areolate. Areoles 0.2-1.2 mm in diam., dispersed or gathered in small clusters, round to slightly angular, flat to slightly convex, usually smooth, chestnut brown, generally epruinose, with a usually darker margin and lower surface. Cortex paraplectenchymatous, c. 15 µm thick; algal layer continuous. Apothecia 0.1-0.6 mm across, persistently immersed, usually slightly crateriform, 1-5 per squamule, with a concave, reddish brown to almost black, smooth or rarely umbonate disc, and an indistinct to very slightly raised thalline margin. Proper exciple thin, 10-15(-20)µm wide; epithecium pale brown; hymenium colourless, 60-90(-110) μm high, hemiamyloid, K/I+ red; 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: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without 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