Myriospora rufescens (Turner ex Ach.) Hepp ex UlothThallus crustose, episubstratic, areolate, forming an extensive, smooth, even crust, dull to dark brown, becoming thinner towards the edge, the areoles contiguous, separated by cracks, angular, (0.3-)0.4-1(-1.5) mm wide, 0.2-0.4 mm thick, flat to concave. Epicortex absent or very thin; cortex 30-40 µm thick, the cells mostly c. 2 µm wide, brown in upper part, colourless in lower part; algal layer 80-100 µm thick, irregularly interrupted by 10-15 µm wide hyphal bundles; medulla 100-250 µm thick, continuous with attaching hyphae, mixed with substrate crystals. Apothecia 0.2-0.4 mm across, 1-2 per areole, immersed, with a black (brown when wet), deeply concave disc concolorous with or darker than thallus, and an entire, slightly raised, black prominent margin. Proper exciple 25-40 µm wide, colourless, but the uppermost cells with dark brown caps; epithecium 10-15 µm high, brown to dark red-brown; hymenium colourless, (60-)80-120(-140) µm high, the hymenial gel hemiamyloid, IKI+ red or blue turning to red; paraphyses simple to sparingly branched and anastomosing 1-1.5 μm thick, the apical cells hardly swollen, cylindrical to clavate; subhymenium 10-30 µm high, opaque, densely inspersed with oil droplets, IKI+ blue; hypothecium 20-35 µm high, IKI-. Asci 100-200-spored, clavate, the apical dome K/I-, 80-100 x 10-20 µm. Ascospores 1-celled, hyaline, ellipsoid, 3-4 x 1-1.5 μm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances. 