Thallus orbicular to spreading, large, 10-25 cm diam., loosely attached, corticolous and saxicolous. Lobes broad, rounded 12-20 mm wide, margins sinuous, sorediate, ± involute, marginal cilia absent. Upper surface pale greenish-grey or greyish-white, smooth, matt, minutely maculate (×10 lens), becoming irregularly cracked with age. Soralia linear, soredia fine, farinose, white. Lower surface black with a broad, brown, naked marginal zone. Rhizines sparse, black, simple. Apothecia not seen. Chemistry: Cortex K+ yellow; medulla K+ yellow → red, C-, KC+ red, Pd+ orange. Salazinic acid and atranorin.