Description: Thallus foliose, homoiomerous, subgelatinous when wet, (2-)3-6(-8) cm across, closely adnate, broadly lobed. Lobes 0.5-1 cm broad, thin, (50-)60-105 µm thick, apically roounded, dark olive-green to brownish black, paler and subtransparent when wet, strongly ridged and often pustulate in young parts, covered in simple or branched, mostly terete, cylindrical isidia (globular when young) which are 0.05-0.15 mm wide and to 0.3 mm long. Lower surface dark olive-green to brownish black, paler than upper surface. Upper and lower cortices absent. Apothecia rare, 0.5-1.5 mm across, with a brown disc and a densely isidiate thalline margin. Proper exciple euthyplectenchymatous. Asci 8-spored, clavate, the apex thick, with a I+ blue apical dome and a I+ blue annulus projecting downwardly. Ascospores 4-5-septate, hyaline, bacilliform to acicular, often curved, 40-80 x 3-6.5(-7.5) µm. Pycnidia common, globose, superficial centrally but immersed marginally, on both sides of thallus. Conidia bacilliform, somewhat swollen towards ends, 4-6 x c. 1 µm, Photobiont cyanobacterial (Nostoc), in long chains. Spot tests: all negative. Chemistry: without lichen substances.
Note: a mainly temperate, probably holarctic lichen found on bark of broad-leaved trees and on epiphytic mosses below the subalpine belt; more common in the past, presently confined to semi-natural, open stands, or to old plantations of Olea in humid areas, and mainly in Tyrrhenian Italy.