Thallus ± crustose, minutely foliose-squamulose, orbicular to spreading, to 8 cm diam., with a prominent, blue-black, byssoid prothallus projecting to 5 mm beyond lobe margins, saxicolous or terricolous. Squamules 0.2-2 mm diam., convex, rosette-shaped, imbricate, margins crenate-incised becoming lobulate, (not to be confused with isidia). Upper surface yellow-brown to grey-blue, shining, whitish or grey-blue-pruinose at margins, without isidia or soredia. Lower surface pale at margins, bluish-black centrally. Apothecia frequent, often clustered, rounded, to 2 mm diam., disc brown at first, becoming dark-brown to black with age, plane to convex, thalline margin prominent, slightly scabrid, ± entire to crenate or rarely sublobulate. Ascospores ellipsoid, 14-18(-20) × 9-13 µm.