Description: Thallus crustose-subsquamulose, episubstratic, greenish grey to olivaceous, dull, corticate, consisting of microsquamules, without a distinct prothallus. Microsquamules deeply incised, crenate, slightly concave to convex, up to 4 mm wide, bearing globose, 50-100 μm wide, isidia-like granules mostly along the margins, sometimes over the whole surface; in thalli with poorly developed microsquamules the granules are smaller and form pale soredia. Apothecia frequent, lecideine, round to irregular in outline, 0.2-1 mm across, at first flesh-coloured, than often patchily or entirely blackening, with a flat to convex disc, and a persistent proper margin. Proper exciple well developed, dark brown in outer part, colourless within, prosoplectenchymatous throughout, but with somewhat expanding lumina towards the periphery and in the lower parts, 50-100 μm wide, the cells 6-12 x 4-8 μm, the pigmented parts K+ purplish, N+ purple-brown, without crystals or granules; epithecium partly hyaline, partly dark brown , the pigmented parts K+ purplish, N+ purple-brown, without crystals; hymenium colourless, 40-55(-60) |μm high; paraphyses mostly simple, the apical cells swollen, 3-5 μm wide; hypothecium colourless. Asci 8-spored, cylindrical-clavate, approaching the Bacidia-type, but the ocular chamber wider, and the axial body never penetrating through the entire d-layer, surrounded by a narrow, darker amyloid layer. Ascospores 3-7-septate, hyaline, needle-like to slightly clavate, coiled in the asci, (35-)40-55(-58) x 1.3-1.7 μm. Pycnidia laminal, globose, erumpent, dark in upper part due to an olivaceous-grey pigment reacting K-, N+ purple-red. Macroconidia hyaline, thread-like, curved, 3-7-septate, (35-)40-57 x (1.2-)1.5-2 μm, the proximal end somewhat truncate. Photobiont chlorococcoid. Spot tests: thallus K-, C- KC-, P-. Chemistry: thallus without lichen substances.
Note: on trees with subneutral bark in nutrient-rich, dusty situations such as in urban parks and forest edges along secondary dirt roads, very rarely also on nutreint-enriched rocks; widespread in Europe and also recorded from Western North America, with a single record from the Eastern Alps (Austria), but probably more widespread; to be looked for in Italy.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by isidia, or isidia-like structures (e.g. schizidia)