Thallus 2-5 cm diam., foliose, single-lobed, attached at a single point by a central or excentric strand, soft, pliable and somewhat leathery when wet, brittle when dry. Upper surface grey-brown, often whitish-pruinose, ± smooth, not noticeably folded, the margins sinuous, ± entire. Lower surface mostly dark brown to black, never pink, rough, rimose-warted, with abundant branched dark brown-black rhizine-like structures which do not anchor the thallus to the underlying rock. Isidia and soredia occasionally present. Medulla loose or compact, not always clearly differentiated from the lower cortex. Photobiont chlorococcoid. Anamorph: not known. Teleomorph: ascomata apothecia, 1-1.5 (-2) mm diam., frequent, particularly towards the margins of the thallus; sessile to shortly stalked. Disc black, smooth with a thick persistent thalline rim and a central protruding ‘button’ of sterile tissue. Interascal tissue of simple or branched, septate paraphyses 1.5-2.5 μm. diam., with ± swollen terminal cells. Asci elongate-clavate, thick-walled, the apical dome K/I+ blue, 8-spored..Ascospores 20-30(-36) × 11-19 μm, becoming brown, muriform. Chemistry: thallus C+ red, K–, KC+ red, Pd– (gyrophoric acid).