Thallus extremely variable, forming orbicular to irregular patches, to 12 cm diam., but generally much smaller. Lobes hollow, varying from very loose and attenuate to moderately compact, the older central lobes and the true marginal lobes which adhere to the substrate are generally more compact and broader while the outer free or loosely attached lobes are repeatedly dichotomously branched and very attenuate, from 0.5-2(-3) mm wide, the uppermost or outermost loosely attached lobes are often considerably elongate and commonly to 5 mm (rarely to 10 mm) between branches and usually somewhat more flattened than the broader lobes within the thallus. Upper surface grey to whitish, with granular soredia developing near apices then spreading and becoming diffuse over the whole surface, occasionally developing into extended, sorediate, coralloid isidia. Medulla thin to thick, white. Lower surface strongly wrinkled, glossy, black, pale brownish at apices of young lobes. Apothecia rare, disc reddish-brown, to 5 mm diam., pedicellate, exciple ribbed, funnel-shaped, ascospores ellipsoid 7-10 × 4.4-6 µm. Chemistry: Chemodeme (i) Cortex K+ yellow; medulla KC+ red, Pd-. Atranorin, chloroatranorin and the physodic acid complex. Chemodeme (ii) Cortex K+ yellow; medulla KC+ red, Pd-. Atranorin, chloroatranorin, the physodic acid complex, physodalic acid and protocetraric acid ±.