Thallus orbicular to spreading, loosely attached, to 8 cm diam., corticolous. Lobes rather narrow, 3-8 mm wide, margins sinuous, ciliate, with ± numerous, dentate laciniae, 2 mm wide and to 4 mm tall, often crowded centrally. Upper surface pale greenish-grey to dark greenish-brown, smooth, matt, faintly maculate at margins, becoming reticulate-cracked centrally, sorediate. Soralia developed mostly on marginal laciniae, later coalescing into ± extensive abraded patches at lobe tips which become hooded or recurved. Apothecia, isidia, pseudocyphellae and pycnidia absent. Lower surface black, with a broad, brown, naked, marginal zone. Rhizines central, black, simple. Chemistry: Cortex K+ yellow; medulla K-, C-, KC+ pink, Pd-, UV ± bluish-white. atranorin, alectoronic and ?-collatolic acids.