Thallus superficial, well-developed, generally 250-800 µm thick (but up to 4-5 mm thick). Secondary areoles subdivided by dark lines into few to numerous (up to 30) small units. Secondary areoles with darker, roundish-angular margins, up to (0.5-)1-5 × 3-8(-15) mm, attached to the substratum by short black stipe-like holdfasts. Algal layer 60-100 µm thick, unpigmented, above a thin black basal layer.
Anamorph: not observed.
Teleomorph: Perithecia entirely immersed in the thallus. Involucrellum absent. Exciple colourless to pale brown, 120-250 µm diam. Ascospores simple in var. trachyticum, 1-septate in the var. subtrachyticum, 13-18 × 5-7 µm.