Thallus corticolous, erect, well-developed, producing numerous, crowded branches. Primary branches rather narrow at base, becoming broadly flattened, 3-6(-11) mm wide, irregularly subflabellate, several narrowly compressed branches produced along the upper margin. Fertile branches narrow, to 2 mm wide, extending beyond sterile branches, to 6 mm long, producing broadly flared apothecia when mature. Upper surface dull grey-green, smooth, transversely annulate-cracked in larger, more mature branches, becoming wrinkled on upper surface of apothecium, lower surface pale, smooth or irregularly wrinkled, upper cortex of mature branches 80-100 µm thick, lower cortex 40-80 µm thick. Algal layer 10-20 µm thick, continuous below upper cortex, rarely occurring on lower side. Apothecia ventral, with broad flared margins, 4-6.5 mm diam., mazaedium soon well exposed, black, loose, globose. Asci cylindrical 40-60 × 5-7 µm. Ascospores spherical, brown-grey, 8-12 µm, surrounded by black carbonaceous material. Chemistry: Sphaerophorin, sometimes with stictic and constictic acids.