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DescriptionThallus: 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.