K. Svenska Vetensk.-Akad. Handl., ser. 3, 7, 4: 229, 1929.
Distribution: C - Sar (Knudsen & al. 2014). S - Bas (Nascimbene & al. 2021).
Description: Thallus crustose, episubstratic, areolate-subsquamulose, brown or reddish brown. Areoles 0.4-3 mm wide, 0.5-1 mm thick, usually contiguous, with an uneven surface. Apothecia lecanorine, round, 0.5-2 mm across, immersed in the areoles, usually 1 per areole, with a reddish brown to black, flat to slightly convex, more or less smooth disc and a raised, thin, thalline margin concolorous with disc. Algal layer c. 200-200 μm thick, strongly irregular and more or less discontinuous. Epithecium brown; hymenium colourless; paraphyses 2-3 μm thick at base; hypothecium colourless. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid, 3-5 x 1.5-2(-3) μm. Photobiont chlorococcoid. Spot tests: thallus and medulla K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a species known from central Europe (Czech Republic, Hungary and Slovakia), as well as Austria, Greece and Sardinia, which was often confused with A. nitrophila and related species.