Thallus: foliose, medium-sized to large, 3-5 cm wide, ±rounded or irregular, deeply and broadly lobate lobes: 2-5 mm wide, (70-)110-200(-300) µm thick, rather few, extended, often repeatedly branched, broadly canaliculated; tips: ±rounded, margins not swollen, coarsely undulate, entire to slightly crenate upper surface: dark olive-green to black, paler and ±transparent when moist, smooth to somewhat pustulate, usually dull, epruinose isidia: laminal, rarely marginal, often numerous, globular, occasionally clavate or cylindrical, not or barely branched, up to 0.3 mm broad, concolorous with thallus or somewhat darker lower surface: paler, grayish or bluish, with scattered or confluent hapters or rhizines forming a down Apothecia: numerous or sparse, laminal, sessile, finally with constricted base, 0.5-1.5(-2) mm wide disc: plane or concave to convex, red-brown or dark red, smooth, sometimes glossy, epruinose thalline margin: ±thick, entire, smooth, or isidiate, lacking a pseudocortex true exciple: euparaplectenchymatous, 45-110 µm thick; cells: (6.5-)10-20(-30) hymenium: hyaline, 85-130 µm tall asci: clavate, 8-spored ascospores: hyaline, ellipsoid to ovoid or subglobose, ends obtuse or ±acute, submuriform to muriform, often with 3 transverse and 1 longitudinal septa, 1524(-28) x 6.5-13(-15) µm Pycnidia: laminal or marginal, immersed or semi-immersed, pale conidia: bacilliform or with slightly swollen ends, 4.5-6 x 1.5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: usually on periodically moistened calcareous or siliceous rocks or on mosses over rock (not observed in the Sonoran Region), in the mountains World distribution: arctic to temperate areas of Europe, Asia and North America, and extending to northern Africa, the Near East, and India Sonoran distribution: Arizona, and southern California. Notes: Collema undulatum var. granulosum is very similar to Collema fuscovirens in having undulate, isidiate lobes, but its lobes are somewhat broader (up to 8 mm) and its spores are bacilliform with obtuse poles and 4-celled. Col-lema subflaccidum occurs on bark and rock, its lobes are flat or somewhat ascending but not undulate and its isidia are more slender (0.05-0.1 mm).