Description: Thallus foliose, homoiomerous, gelatinous when wet, often forming irregular rosettes, 2-3(-5) cm wide, deeply and broadly lobed. 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 with white hapters. Upper and lower cortices absent, but medulla partially paraplectenchymatous. Apothecia rather rare, with slightly constricted base, 1-2(-2.5) mm wide, with a brown disc and a thin, granulose to lobulate thalline margin. True exciple thin, paraplectenchymatous; hymenium colourless, 130-170 µm tall. Asci 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, pale. Conidia bacilliform, usually slightly swollen at the ends, 4.5-6 x 1.5-1.8 µm Photobiont cyanobacterial (Nostoc), 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.