Distribution: C - Tosc, Laz, Sar (Rizzi & al. 2011). S - Pugl, Cal (Puntillo 1996), Si (Grillo & Carfì 1997, Grillo & Caniglia 2004).
Description: Thallus crustose, thinly episubstratic, c. 40 μm thick, white to yellowish white, continuous and smooth or finely rimose, forming well-delimited, 1-2 cm wide, often confluent orbicular patches, without a distinct prothallus. Apothecia arthonioid, emarginate, black, epruinose, dull, semi-immersed in the thallus, rounded, ellipsoid or irregularly angular, 0.4-0.9 mm across. Proper exciple poorly developed, blackish; epithecium black, 7-10 μm high, K-; hymenium pale ochraceous yellow, 75-95 μm high, I+ blue; paraphysoids branched and anastomosing, very thin, with weakly swollen apical cells; hypothecium black to brown-black, wedge-shaped, 35-45 μm high. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 3(-4)-septate, subclavate, with one of the apical cells slightly larger than the others, becoming slightly narrower toward the other end, hyaline, ellipsoid, 15-20 x 5-8 μm. Pycnidia rather frequent, black, somehow shiny. Conidia bacilliform, straight, 7-9 x c. 1 μm. Photobiont trentepohlioid. Spot tests: thallus K- or K+ pale yellow, C-, KC-, P-. Chemistry: unknown.
Note: a southern species in Europe, found on smooth bark in humid, coastal situations, most often with Dirina ceratoniae and Thelopsis isiaca, mostly 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)