Thallus to 10 cm diam., composed of a few to numerous hanging, strap-shaped lobes 1-4 mm wide, dichotomously branched in one plane, the branching widely divergent with short side branches. Upper surface grey-white to cream, matt, often rough with isidia or small folioles. Lower surface usually channelled, uniformly grey-black or ± mottled black and brownish-white or pinkish, with incurved margins concolorous with the upper surface, rhizines lacking. Photobiont trebouxioid. Anamorph: not known. Teleomorph: ascomata apothecia, infrequent, to 1.5 (-3) mm diam., stalked, lateral, on curved part of branches, irregular in form and sometimes with split margins. Discs flat to concave, olive to dark red-brown. Asci 30-40 × 14-16 µm, clavate, Lecanora type, 8-spored. Ascospores 7.5-10 × 4-5.5 µm, ellipsoidal, hyaline, aseptate, smooth, without an epispore, gelatinous sheath or appendages. Chemistry: cortex K+ yellow (atranorin); medulla C– K–, KC–, Pd–, UV– (physodic acid). In var. ceratea (the commoner taxon, especially in northern Britain) the medulla is C+ red due to the presence of olivetoric acid.