Thallus orbicular to spreading, loosely attached, to 20 cm diam., saxicolous or corticolous. Lobes rounded (5-10 mm wide), subimbricate, margins entire, black, shining. Upper surface smooth, pale grey, whitish ashy-grey or greenish-grey with a pale bluish tinge, pseudocyphellae prominent in a white reticulum, becoming deeply cracked centrally, distinctly white-maculate near lobe apices or often white-pruinose at margins, isidiate-sorediate. Isidia laminal, rarely at margins, scattered, corralloid-pustular, clustered and deformed, developing from cortex near margins of cracks or pseudocyphellae, with age becoming coarse granular-sorediate, central parts often forming a dense, coralloid, isidiate-sorediate mat. Lower surface black, shining, with a dark brown, naked marginal zone often present, rhizinate centrally. Rhizines black, simple or branched. Apothecia occasional, sessile to subpedicellate, to 15 mm diam., disc red-brown to dark brown, matt, plane or concave, margins entire at first, becoming fissured with age, sinuous or crenate, often inflexed and obscuring disc, becoming isidiate-sorediate, thalline exciple strongly maculate-cracked, pseudocyphellate. Ascospores ellipsoid, 9.5-12 × 6.5-8 µm. Chemistry: Cortex K+ yellow; medulla K+ yellow ± red, C-, KC+ red, Pd+ orange. Salazinic acid and atranorin.