Thallus ± orbicular to irregularly spreading, rather loosely attached, 3-8(-15) cm diam., corticolous. Lobes ± rounded, 2-8 mm wide, rather short, ± free at margins, imbricate centrally, margins entire or slightly notched, becoming ± pectinate and isidiate, slightly thickened, subascendent or inrolled, ± sinuous, crisped. Upper surface dark bluish-grey, suffused reddish-brown in parts when wet, distinctly white-maculate (×10 lens) or with larger, irregular areas free of algae, pale olive-buff to olive-brown or reddish-brown when dry, smooth or slightly uneven, shining, sparsely to densely isidiate. Isidia terete, simple, globular at first, slightly constricted at base, becoming coralloid-branched, apices globose, to 0.6 mm tall, concolorous with thallus, slightly paler at base, mainly laminal and often in a thick, diffract crust, rarely marginal. Medulla white. Photobiont blue-green. Lower surface pale buff or whitish at margins, darkening centrally, underside of margins often ± olive-brownish, smooth to wrinkled or scrobiculate, not bullate, delicately white- or buff-pubescent towards margins, often with a shining, wrinkled, glabrous marginal zone, pubescence intermixed with sparse to numerous, shining black hairs, often ± reticulate patches, with bundles of ± squarrose, black or brown rhizines occasional at centre. Apothecia not seen. Chemistry: 3 unidentified triterpenes.