Description: Thallus crustose, episubstratic, rimose-areolate, 0.2-0.3 mm thick, grey-white to pale blue-grey, forming poorly delimited, small, up to c. 2(-3) cm wide patches, often with a dark prothallus. Cortex 15-25 µm thick; medulla white, I-. Areoles 0.5-0.7 mm wide, mostly flat, the periphereal ones somehow darker, more or less elongate and indistinctly radiating. Apothecia lecanorine-aspicilioid, immersed in the areoles, 0.2-0.3 mm across, 1-3(-4) per areole, with a black, concave to flat, epruinose or rarely thinly pruinose disc, and a thin, often poorly evident thalline margin reacting K-. Epithecium olive-green to olive-brown, N+ emerald green; hymenium colourless, 100-115 µm high, I+ reddish brown; paraphyses submoniliform c. 2 µm thick in lower part; hypothecium colourless, 40-50 µm high. Asci 8-spored, broadly clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores (15-)17-20(-22) x 9-12 µm. Conidia thread-like, 16-18 x c. 0.5 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-. Chemistry: unknown.
Note: on weakly calciferous rocks in dry situations, mostly near or above treeline. A poorly understood species, which was frequently confused with A. verruculosa in the past.