Description: Thallus crustose, episubstratic, areolate-subsquamulose, the areoles sparse or gathered in small clusters, pale brown except at the brown-black margin, flat to slightly convex, 0.4-2.5 mm wide. Cortex 60-70 μm thick; algal layer of uniform thickness, continuous. Apothecia aspicilioid, at first punctiform, then with an expanded, round to elliptical or irregularly shaped, flat disc occupied by a single central umbo, with a poorly evident thalline margin. Epithecium brownish; hymenium colourless, 140-200 μm high; paraphyses abundantly branched and anastomosing, 1.5-2 μm thick at base; hypothecium colourless. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, globose or subglobose, 3-5 x 3-4 μm. Photobiont chlorococcoid. Spot tests: cortex K- C+ pink, KC+ pink, P- (reactions often fleeting and observable only on thick sections under the microscope!). Chemistry: cortex with low quantities of gyrophoric acid.
Note: on basic siliceous rocks wetted by rain, mostly below the montane belt, perhaps a parasite of Aspicilia, at least when young. Described from Southern France, and known from a few localities in the Mediterranean area.