Description: Thallus crustose, episubstratic, rimose at the edge, otherwise areolate, grey to blue-grey, rarely grey-brown, forming well delimited patches to 20 cm across, sometimes delimited by a dark prothallus. Areoles angular to irregular, flat to convex, (0.2-)0.4-1(-2) mm in diam., contiguous, separated by distinct cracks. Cortex brownish in upper part, sometimes covered by an epinecral layer. Apothecia lecanorine-aspicilioid, (0.1-)0.4-0.8(-1.3) mm across, 1(-5) per areole, round to angular, with a black, concave to flat, epruinose disc with a rough surface, and a rather thick, raised thalline margin. Epithecium olive to olive-brown, without crystals, N+ emerald green, K+ brown; hymenium colourless, (80-)120-150(-200) µm high, I+ wine-red to yellow-green; paraphyses slightly branched and anastomosing, 1.5-2 µm thick, submoniliform in upper part, with globose to subglobose, 4-5 µm wide uppermost cells; hypothecium colourless, I+ persistently blue or partly turning yellow-green. Asci (4-)6(-8)-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid to subglobose when young, (14-)18-30(-35) x (7-)10-16(-22) µm. Pycnidia with a black, punctiform ostiole. Conidia thread-like, straight, 6-12 x c. 1 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-. Chemistry: aspicilin.
Note: on siliceous rocks wetted by rain, with a wide altitudinal range. Very heterogeneous both morphologically and ecologically, and in need of revision. See also note on Sagedia zonata.