Description: Thallus foliose, homoiomerous, subgelatinous when wet, deeply and broadly lobed, often forming irregular, 2-3(-5) cm wide patches. Lobes often crowded and imbricate, 0.5-1(-6) mm wide, rather thin (70-200 µm when wet), rounded, flat or concave, often ascending and ear-shaped, dark green, olive or greenish black (more green in shaded situations), with flattened, c. 0.15-0.3 mm wide isidia which sometimes obscure the thallus. Lower surface paler, with white hapters. Upper and lower cortices absent, but the central thallus layer paraplectenchymatous. Apothecia rather rare, lecanorine, sometimes slightly constricted at base, 1-2(-2.5) mm across, with a brown disc and a thin, granulose to lobulate, usually persistent thalline margin. Thalline exciple ecorticate or with a primitive pseudocortex; proper exciple thin, sub- to euthyparaplectenchymatous; hymenium colourless, 130-170 µm high, I+ blue; paraphyses simple or sparingly branched in upper part, 1.5-2 µm thick at mid-level, the apical cells up to 4.5 µm wide; hypothecium colourless to pale yellow, I+ blue. Asci (4-6-)8-spored, narrowly clavate, the apex thick, with a I+ blue apical dome and a I+ blue annulus projecting downwardly. Ascospores 3-septate (rarely submuriform), slightly constricted at septa, hyaline, ovoid to subellipsoid with rounded ends, (18-)26-34(-47) x (9-)13-15(-17) µm. Pycnidia immersed, paler than thallus. Conidia bacilliform, usually slightly swollen at both ends, 4.5-6 x 1.5-1.8 µm Photobiont cyanobacterial (Nostoc, the cells in short chains with less than 4 cells). Spot tests: all negative. Chemistry: without lichen substances.
Note: a mainly mild-temperate lichen found both on calcareous rocks and soil, often in rather disturbed habitats such as walls in villages below the subalpine belt; most common in central and southern Italy; the mostly saxicolous, smaller var. metzleri - in my opinion - is hardly worth of an independent taxonomic rank.