Trapelia coarctata (Sm.) M. ChoisyThallus crustose, whitish, pale grey to pinkish-grey, thin, continuous to rimose, rarely areolate, sometimes with a whitish prothallus. Apothecia frequent, round at least when young, sessile, up 0.3-0.8(-1.2) mm across, with a pinkish-grey to pale or dark reddish-brown, flat to slightly convex disc and a concolorous, finally often excluded proper margin surrounded by a thin, whitish pseudothalline margin in young apothecia; immature apothecia frequent, appearing as white dots on the thallus. Proper exciple of colourless hyphae embedded in a colourless to weakly pigmented gel; epithecium almost colourless to pale yellowish brown; hymenium colourless, 90-140 µm high; paraphyses coherent, thin, densely branched and anastomosing, not thickened at apex; hypothecium colourless to yellowish. Asci 8-spored, cylindrical-clavate, unitunicate, thin-walled, the apical dome K/I-, or weakly K/I+ blue, <i>Trapelia</i>-type. Ascospores 1-celled, hyaline, ellipsoid, 14-26(-28) x 7-13 µm, without a perispore. Pycnidia immersed. Conidia hyaline, thread-like. Photobiont chlorococcoid. Spot tests: thallus K-, C+ red, KC+ red, P-, UV+ bluish white. Chemistry: thallus with gyrophoric acid.