Description: Thallus crustose, episubstratic, up to 120 µm thick, smooth to finely rimose, olive-brown to dark brown, subgelatinous when wet, the hyphae vertically oriented. Perithecia scattered, black, more or less immersed in the thallus to clearly projecting, sometimes partly covered by a thin thalline layer, globose or slightly flattened at apex, often depressed dear the ostiole, 0.12-0.3 mm in diam. Involucrellum absent; exciple dark throughout or slightly paler in lower part, more or less cellular, thicker around the ostiole; hamathecium of richly branched and anastomosed pseudoparaphyses, the hymenial gel I-. Asci 8-spored, ovoid to subcylindrical, usually stalked, with two functional wall layers, K/I-, the wall thickened above, with an ocular chamber, fissitunicate, with a distinct extruded rostrum at dehiscence. Ascospores 1-septate, hyaline, ovoid to ovoid-fusiform, one cell often wider than the other, 17-26 x 6-12 µm. Pycnidia black, immersed to slightly projecting, the conidiogenous cells cylindrical, phialidic. Conidia oblong-ellipsoid, 2.9-3.3 x c. 1.2 µm. Photobiont cyanobacterial, the cells globose, 3-9 μm, or sometimes slightly elongate and up to 12 μm long, densely aggregated in irregular clusters and enclosed in yellowish to slightly brownish gelatinous sheaths. Spot tests: all negative. Chemistry: without lichen substances.
Note: on often submerged siliceous rocks along streams and along the margins of lakes; widespread in the Holarctic region, but not common. A mainly western species, reported from Sardinia; also recorded from the Western Alps (France) in sites with a untypical ecology, and therefore these records in need of confirmation.