Description: Thallus foliose, homoiomerous, gelatinous when wet, more or less deeply lobed, membranous, closely adpressed, 3-6 cm wide. Lobes 5-8 mm wide, 0.1-0.2 mm thick, dark olive-green to black, the surface conspicuously folded, with ascending, entire or isidiate, never swollen margins. Isidia abundant, c. 0.1 mm thick, to 1.5 mm long, globose when young, then cylindrical and coralloid, usually crowded and forming a dense, coarsely areolate crust on older parts of thallus. Upper and lower cortices absent. Apothecia and pycnidia unknown. Photobiont cyanobacterial (Nostoc, the cells arranged in long chains). Spot tests: all negative. Chemistry: without lichen substances.
Note: an arctic-alpine species found on basic siliceous rocks, more rarely on limestone, in humid situations near or above treeline; another record is in Swiss territory, near the Italian border with Lombardy.