Thallus to 5-7 cm diam., often smaller, level with or sunken into the substratum. Lobes 5-10 mm wide [sometimes broader in Scandinavian material], to 35 mm long, concave to ear-shaped, with ascending, entire or ± eroded, thickened and sometimes inrolled margins. Upper surface grey-brown to olive brown (rarely olive green in fully hydrated conditions), smooth, glabrous in part or ± thinly tomentose to somewhat scabrous. Isidia to 1.5 mm diam., numerous, button-like, resembling cephalodia, crowded and contiguous, sometimes overlapping or widely dispersed. Lower surface pale, with often rather indistinct white to pale grey, rarely pale brown anastomosing veins and discrete to confluent unbranched pale to brown rhizines. Photobiont cyanobacteria (Nostoc). Anamorph: not known. Teleomorph: ascomata apothecia, not known in the British Isles; on shortly elongate lobes, the disc 3-7 mm diam., saddle-shaped. Ascospores 49-59 x ca 5 µm. Chemistry: thallus with no positive reactions. No lichen products detected by TLC.