Distribution: N - VG (TSB 10023), Ven (Nascimbene & al. 2021), TAA, Emil (Fariselli & al. 2020). C - Tosc, Marc (Nimis & Tretiach 1999), Umb (Nimis & Tretiach 1999, Ravera & al. 2006, Panfili 2007), Laz (Nimis & Tretiach 2004), Abr (Tretiach 2015b, Gheza & al. 2021). S - Camp (Aprile & al. 2003b, Nimis & Tretiach 2004), Pugl (Nimis & Tretiach 1999), Si (Caniglia & Grillo 2005, 2006).
Description: Thallus crustose, endosubstratic or (rarely) very thinly episubstratic, mostly not evident, when episubstratic forming a very thin, grey-white crust. Apothecia arthonioid, immarginate, black, epruinose, round to irregular in outline, up to 0.2 mm across, scattered or confluent in clusters of 2-3, flat to slightly convex, located in shallow depressions of the rock. Epithecium greenish black; hymenium colourless or pale yellow, 35-45 µm high; hypothecium brown-black. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, hyaline, 8-16 x 3-6 µm, pointed at one end, broadly rounded at the other. Photobiont absent or chlorococcoid. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: an early coloniser on exposed calcareous rocks below the subalpine belt; overlooked and probably more common, especially in the eu-mediterranean belt. It also occurs in warm-dry Alpine valleys.