Thallus wide-spreading, to 5-10 (-20) cm diam. (to 35 cm diam. in Scandinavian material), subcoriaceous, loosely attached. Lobes 10-30 (-40) mm wide and to 10-18 cm long, rounded, the margins ± raised. Upper surface roughened, blue- to brown-green when hydrated, grey-brown to brown when dry, matt, scabrid but not tomentose. Lower surface brown to black-brown with distinct veins in the central region, the veins 0.8-1.2 mm broad, grey to ochraceous brown towards the margins, with the tissue between the veins 1-2 mm broad and similarly coloured. Rhizines 2-3 (-5) µm long, dark brown to black, fibrillose to fasciculate, separate, often growing together at their tips and then forming a ± continuous mat. Photobiont cyanobacteria. Anamorph: not known. Teleomorph: ascomata apothecia, not seen in British material; disc 3-6 mm diam., saddle-shaped, dark reddish brown, on shortly extended thalline lobes. Ascospores 75-90 × 3-5 μm, filiform, 3-septate. Chemistry: thallus with tenuiorin, methyl gyrophorate, gyrophoric acid (C+ red), T1, T2, T3, T6 and two unidentified triterpenoids.