Thallus: foliose, usually medium-sized, a few cm wide, ±adnate, rounded, deeply and broadly lobate lobes: ±radiating, extended, deeply and furcately branched or irregularly branched, lobulate; lobules: 2-4 mm wide, 140-300 µm thick, imbricate, concave or with ascending, coarsely undulate, entire margins; tips: ±rounded, not swollen upper surface: dark olive green to blackish, rarely paler, ±transparent when moist, smooth, not or slightly glossy, epruinose isidia: numerous, globular, laminal, occasionally somewhat elongated or scale-like, 0.1-0.2 mm wide, concolorous with thallus lower surface: paler than the upper surface Apothecia: occasionally present, laminal or marginal, sessile and finally with constricted base, not stipitate, 0.5-1.5 mm wide disc: plane, finally convex, red-brown or dark red, smooth, slightly glossy, epruinose thalline margin: thin or thick, entire or crenate, ±smooth, sometimes with a poorly developed pseudocortex true exciple: euparaplectenchymatous, 45-130 µm thick; cells: 8-16 µm wide hymenium: hyaline, 85-105 µm tall asci: clavate, 8-spored ascospores: hyaline, oblong, straight, with rotund or obtuse ends, 4-celled, ±constricted at septa, 17-30 x 6.5-9 µm Pycnidia: usually marginal, immersed to semi-immersed, pale conidia: bacilliform or with slightly swollen ends, 4-4.5 x c. 1-1.5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on periodically moistened calcareous rocks, exceptionally on siliceous rocks or on mosses over rocks (not observed in the Sonoran Region) World distribution: North America and Europe Sonoran distribution: a few localities in northern and eastern Arizona above 2000m. Notes: Collema fuscovirens is similar to Collema undulatum var. granulosum but its thallus is usually somewhat paler and its lobes are slightly pustulate and less distinctly undulate. Furthermore, Collema fuscovirens has broadly ellipsoid or fusiform, submuriform ascospores.