Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: foliose, medium-sized to large, 2.5-6 cm wide, thin, membrane-like, ±rounded, loosely attached, broadly and ±deeply lobate lobes: 0.5-1.5(-3) cm wide, thin (70170 µm), not swollen, few, ±rounded, often partly ascending, imbricate, radially or irregularly folded; margins: ±entire, sometimes revolute or ascending upper surface: smooth to slightly pustulate, black, usually dull isidia: numerous, often crowded, laminal, at first globose but soon flattened and scale-like lower surface: usually paler than upper surface, pale gray or blue, sometimes folded or ridged Apothecia: rare, laminal, sessile with constricted base, 1.5(-2.5) mm wide disc: flat to slightly convex, pale or dark red, usually dull, smooth, epruinose or sometimes pruinose when old thalline margin: smooth, usually not prominent, with thick, 40-90 µm wide pseudocortex, especially at lower parts true exciple: rather thin, subparaplectenchymatous to nearly euthyplectenchymatous hymenium: hyaline, 90-130 µm tall asci: narrowly clavate, 8-spored ascospores: hyaline, ellipsoid to fusiform, 4-6-celled, not constricted at septa, (20-)26-34(-40) x 6-6.5 µm Pycnidia: immersed, laminal, pale conidia: bacilliform or with slightly swollen ends, (3-)4-4.5(-6) x 1-1.5(1.8) µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on bark or damp rock (usually siliceous), often among mosses, in mountainous regions World distribution: from the arctic to southern temperate areas of Europe, Asia and North America, northern Africa, Near East, India, Oceania, and Australia Sonoran distribution: central and southeastern Arizona above 1500 m. Notes: Collema flaccidum is distinguished by its large, broad-lobed thallus with distinct ridges and scale-like isidia. Collema subflaccidum lacks distinct ridges and has small, globular isidia.