Thallus orbicular to spreading, loosely attached, 5-15 cm diam., corticolous or saxicolous. Lobes rounded, 8-15 mm wide, margins entire, often strongly sinuous, black, shining, ciliate, cilia rather sparse, 0.5-2 mm long. Upper surface pale greenish-grey or bluish-grey in damp habitats, to white or greyish-white in exposed habitats, smooth, matt, often wrinkled and usually cracked in older parts, submarginally sorediate. Soralia linear, soon eroding a large area and causing margins to become strongly revolute or capitate-hooded, soredia fine, powdery, white. Lower surface black and shining, with a conspicuous dark brown, naked marginal zone. Rhizines central, long, black, simple. Apothecia rare, pedicellate, to 6 mm diam., disc concave to ± plane, matt, pale brown to red-brown, imperforate, margins thick, inflexed, sorediate. Ascospores 25-28 × 16-18 µm. Pycnidia occasional, minute, black, punctiform, mainly marginal. Chemistry: Cortex K+ yellow; medulla K+ persistent yellow, C-, KC-, Pd+ pale orange. Atranorin and stictic acid.