Thallus rosette-forming at first, becoming irregular and forming extensive, ragged-edged patches, individual thalli seldom exceeding 5 cm diam., corticolous, rarely saxicolous or terricolous. Lobes very numerous, small, delicate and fragile, 0.5-0.8 mm wide and to 5 mm long but usually much shorter, irregularly branched, sometimes subpalmate towards perimeter, mostly closely contiguous throughout entire length, often imbricate centrally and there sometimes ± ascending, margins sinuous, entire or notched, hollow, lower side of internal cavity blackened, apices ± elevated, ± pale brown or red-brown. Upper surface concave or plane, shining, pale green-grey or fresh lettuce-green, in exposed situations becoming suffused-brownish, margins not, or only sparingly, blackened, with a faint, white, irregular, incomplete reticulum of maculae (×10 lens) best seen at apices and margins. Perforations numerous, median on main lobes, depressed, oval or rounded, gaping, with an inrolled edge (-type), 0.2-0.5 mm diam. Soredia arising from upper surface and margins of perforations, derived from erosion of isidia-like vesicles. Vesicles at first simple, or several closely contiguous, hollow, nodular, proliferating to form verruciform clusters which eventually cover older parts of thallus, often apically abraded. Apothecia not seen. Chemistry: Stictic, constictic, norstictic (tr.) and menegazziaic acids and atranorin (±); medulla K+ yellow → orange, C-, KC+ orange, Pd+ orange.