Synonyms: Acarospora austriaca H. Magn.; Acarospora obscura H. Magn.
Distribution: N - Ven (Knudsen & Kocourková 2020). C - Sar (Knudsen & Kocourková 2020).
Description: Thallus crustose, epilithic, areolate. Areoles 0.2-3 mm diam., usually contiguous and forming a rather well-delimited thallus, angular to almost round, sometimes the peripheral ones indistinctly lobulate, flat to slightly convex, usually dark brown with a blackish margin, not pruinose. Apothecia 0.2-1 mm across, usually immersed, 1-5 per areole, with a flat to slightly convex, reddish brown to black-brown disc, and a slightly raised thalline margin; proper margin sometimes visible as a ring inside the thalline margin. Epithecium pale brown; hymenium colourless, 50-100 μm tall; paraphyses 2-3 µm thick at base, the apical cells 3-5 µm wide; hypothecium colourless. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, narrowly ellipsoid, 3-5 x 1.5-2 μm. Photobiont chlorococcoid. Spot tests: all negative. Chemistry: no lichen substances.
Note: on intermediate, base-rich siliceous rocks, from the submediterranean to the alpine belt; known from Central and Southern Europe. For further details see Knudsen & Kocourková (2020).