Description: Thallus crustose, episubstratic, rather thick, continuous to rimose, ecorticate, chalky white to yellowish white, somewhat pulverulent, sometimes sterile and with numerous,evenly scattered, pale brown granular flecks. Apothecia black, subimmersed in the thallus, rarely adnate, very variable in form, round and 0.3-0.7 mm across, or lirelliform, broadly or narrowly oblong, 0.3-1 x 0.3-0.5 mm, simple or slightly branched, straight or curved, with a black, expanded, flat to slightly convex, often blue-grey-pruinose disc, and a usually undulating, scarcely raised, finally often excluded proper margin. Proper exciple black, carbonized, at maturity extending below the hymenium, K+ dark green; pseudothecium pale brown, 15-25 µm thick; hymenium colourless, 60-90 µm high, I+ pale red or I+ blue; paraphysoids richly branched and anastomosing, up to 1.5 µm thick, the apical cells not or only slightly swollen; subhymenium brown, 20-35 µm high, I+ pale blue; hypothecium black. Asci 8-spored, cylindrical-clavate, with an entirely amyloid endoascus, grumulosa-type. Ascospores (6-)8-9(-12)-septate, hyaline (overmature spores brown), narrowly fusiform, (17-)23-35(-41) x 3-4.5 µm, the wall thin, not swollen at septa, surrounded by a thin, sometimes poorly evident gelatinous sheath. Pycnidia black, immersed, subglobose. Conidia straight, bacilliform, 4-6 µm long. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-, UV+ white, K/UV+ mauve. Chemistry: confluentic and 2’-0-methylmicrophyllinic acids.
Note: a mild-temperate, mainly western lichen found on the rough, acid bark of very old isolated trees, especially oaks; declining, especially in northern Italy, and presently mainly Tyrrhenian.
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)