Thallus foliose, heteromerous, dorsiventral ± orbicular in outline, rarely more than 10 cm diam., corticolous or saxicolous. Lobes adjacent or imbricate, broadly cuneate to flabellate, the margins slightly thickened and curled downwards. Upper surface glabrous, smooth and shining, or minutely wrinkled or scabrid, colour usually ± leaden-grey but sometimes brownish-grey, bluish to almost black, often distinctly ridged, the ridges being arranged in curved concentric lines parallel with the lobe apices and reflecting the attachment of rhizines on the lower surface. Upper cortex of paraplectenchymatous cells, arranged in ± parallel lines radiating along the lobes from centre to periphery, a diagnostic character visible in larger specimens as faint striae (×10 lens). Photobiont blue-green, . Lower surface corticate, often densely covered with long, silky rhizines. Rhizines pale, white or grey to dark bluish-black or black. Apothecia biatorine, adnate, lacking a proper margin, ± hemispherical, rounded to irregular. Ascospores simple, colourless, ellipsoid, 8 per ascus. Pycnidia frequent to sparse in fertile specimens, ± wart-like, dark red-brown to black. Conidia rod-shaped.