Thallus loosely attached, large (5-15 (-20) cm diam.), often forming extensive patches. Lobes sublinear to ± irregular, 5-10 (-15) mm broad, broadly rounded at the apices, contiguous but often overlapping and becoming crowded centrally; margins often ascending, wavy and often incised, irregularly lobulate or isidiate, with marginal cilia usually present, often associated with incisions. Upper surface grey or grey-green, matt, sometimes faintly maculate, smooth or small-pitted towards the centre. Isidia fragile, marginal and laminal, cylindrical or lobulate, often becoming coralloid-branched, brown-tipped and frequently with accompanying black cilia, sometimes forming very dense clusters centrally. Lower surface black with a broad, brown erhizinate marginal zone. Rhizines dense, simple. Anamorph: conidiomata pycnidia, rare, not reported for British material. Teleomorph: ascomata apothecia, very rare, submarginal, stalked, 3-8 mm diam., the disk imperforate, thalline exciple isidiate. Ascospores 21-31 × 11-15 μm. Chemistry: cortex K+ yellow; medulla C–, K+ yellow, KC+ yellow-orange, Pd+ yellow-orange, UV– [atranorin, stictic (major), constictic acids (minor) and a range of accessory compounds including menegazziaic acid].