Description: Thallus small-fruticose, gelatinous when wet, dark olivaceous brown to black, forming spreading cushions, consisting of decumbent to ascending, terete, often finely striate, mostly dichotomously branched, up to 2 mm long lobes with swollen, up to 0.3 mm wide apices containing initially globose, finally bursting open and cup-like hormocystangia producing 25-35 x 10-15 μm hormocysts, Apothecia (pycnoascocarps) very rare, terminal, globose, 0.2-0.4 mm across, with a convex, blackish disc and a thick, smooth, persistent thalline margin. Proper exciple very thin, of parallel hyphae; epithecium yellowish brown; hymenium and hypothecium colourless, I+ reddish brown, K/I+ blue; paraphyses mostly simple, not apically thickened, adglutinated; hypothecium colourless. Asci 8-spored, prototunicate, cylindrical, without a distinct apical apparatus. Ascospores 1-celled, hyaline, globose, 15-20 μm. Pycnidia apical, immersed. Conidia bacilliform. Photobiont cyanobacterial (Nostoc, in chains), the individual cells 4-5 μm wide. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on more or less calciferous rocks with periodical percolation of water in cool situations; widespread in the Northern Hemisphere (Scandinavia, North America), but not common; rarely collected in the Alps, being only known from Switzerland. To be looked for in the Italian Alps.