Synonyms: Acarospora rehmii H. Magn.; Acarospora tongletii f. rehmii (H. Magn.) Clauzade & Cl. Roux; Acarospora tongletii var. paupera (H. Magn.) Clauzade & Cl. Roux
Distribution: N - VG, Lig.
Description: Thallus crustose, epilithic, rimose-areolate, well delimited, whitish, grey to yellowish brown. Areoles small, usually not well-visible because hidden by the numerous aothecia. Algal layer discontinuous, interrupted by vertically oriented hyphal bundles. Apothecia lecanorine, 0.2-0.6 mm across, 1-3(-5) per areole, at first immersed, then more or less protruding, round to angular or slightly elongated, sometimes confluent, with a concave, smooth to slightly rugose, dark brown disc and a prominent, entire thalline margin. Epithecium yellowish brown, K+ yellow torning red; hymenium colourless, 60-120(-130) μm tall; paraphyses 1.5-2 μm thick at base, 3-5 μm at apex; hypothecium colourless, K-. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid to subcylindrical, 3-6.5 x 1.5-2 μm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-; apothecia K+ yellow turning red (red crystals). Chemistry: thallus without lichen substances; apothecia (epithecium and thaslline margin) with norstictic acid.
Note: a temperate to boreal-montane, probably circumpolar species, in Italy most frequent on base-rich sandstone walls, but much overlooked.