Distribution: C - Sar. S - Pugl (Nimis & Tretiach 1999), Cal (Nimis & Puntillo 2003, Puntillo 2011, Ravera & al. 2022b), Si (Nimis & al. 1994).
Description: Thallus crustose, episubstratic, continuous to rimose, chalky white, c. 100 µm thick, forming slightly raised, irregularly rounded, often confluent patches. Apothecia arthonioid, numerous, round to slightly elongate, 0.1-0.6 x 0.1-0.5 mm across, black but thinly white-pruinose, immersed and level with thallus. Proper exciple poorly developed, of dark hyphae; epithecium brown to brown-black, K-; hymenium colourless to patchily brown, 50-60 µm high; paraphysoids numerous, the apical cells swollen, 3.5-4.5 μm wide, with a dark brown cap; hypothecium dark brown to black, wedge-shaped, 45-55(-70) μm high, K-. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome, and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, not constricted at septum, hyaline, ellipsoid with rounded ends, (8-)12-15 x (3.5-)5-6 μm. Pycnidia black, immersed. Conidia bacilliform, 5-9 x c. 1 µm. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a Mediterranean-Atlantic species found on soft limestone in sheltered situations, often with Opegrapha durieui; mainly Tyrrhenian in Italy.
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)