Thallus corticolous, subimbricate, usually of several, horizontal, somewhat overlapping branches. Fertile branches flattened, with a distinct upper and lower surface, to 5 cm long and 2.6 mm wide, with numerous, short, flattened, sterile branchlets crowded at base, short secondary branchlets produced irregularly along margins. Upper surface dark green, smooth, convex, transversely annulate-cracked, with small isidia-like structures produced along cracks, especially over apothecium, lower surface pale or whitish, upper cortex 90-130 µm thick, lower cortex 50-90 µm thick. Algal layer 25-45 µm thick, continuous beneath upper cortex, rarely occurring on lower side. Apothecia 2-8 mm diam., subterminal, typically wider than supporting branch, with numerous small outgrowths or branchlets forming along lower margin, mazaedium ventral, covered, finally exposed through small opening in enclosing receptacle which is always persistent and ± partially covers mazaedium. Asci cylindrical, 50-65 × 5-7 µm. Ascospores spherical, brown (10-)12-16(-18) µm diam., commonly surrounded by dark carbonaceous material. Chemistry: K-, Pd+ red. Sphaerophorin and protocetraric acid.