Thallus: foliose, small to large, up to 20 cm wide, rounded or irregular, dying from the center, deeply lobate lobes: extended, often radiating, furcate, usually deeply concave and distinctly channeled with ascending, wavy or sinuose margins; margins: thin or slightly swollen, 130-475 µm thick, entire or incised upper surface: dark olive-green or black, ±smooth, dull or somewhat glossy isidia: absent or present, marginal, globose to broad clavate lower surface: concolorous or paler than upper surface, with scattered or confluent, pale hapters Apothecia: absent or common, usually marginal, sessile to finally stipitate disc: plane, concave or convex, red to dark red-brown or black, smooth, epruinose, dull or slightly glossy thalline margin: thin, smooth and entire to granulose or crenulate, inconspicuous or slightly prominent, lacking a pseudocortex true exciple: rather thick, 40-105 µm wide, euparaplectenchymatous; cells: 6.5-15 µm wide hymenium: hyaline, 90-130 µm tall asci: narrowly clavate, 8-spored ascospores: hyaline, ellipsoid, with ±acute ends, usually submuriform, rarely 4-celled or eumuriform, 18-32(-40) x 8-13 µm Pycnidia: usually marginal, ±immersed or sessile, pale conidia: bacilliform or with slightly swollen ends, 4-5 x 1.2-1.8 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: usually on calcareous (also on siliceous) rocks or calciferous soil, mainly in mountains World distribution: arid to arctic/ alpine areas of North America, Europe, Macaronesia, northern Africa, Near East, Siberia, and India Sonoran distribution: scattered in mountains of Arizona, southern California (Channel Islands), Baja California, Baja California Sur, Sonora and Chihuahua. Notes: Collema cristatum is quite easily recognized by its deeply branched and channeled, crisped lobes. The species usually growths on rock and sand filled rock clefts, but also occurs on soil.