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

Thallus: crustose (to subfoliose), like a thin membrane on the soil, shrinking and almost disappearing when dry, small to rather large, up to 5 cm wide, starting as granules that coalesce to form more continuous thallus, 100-500 µm thick lobes: lacking or indistinctly differentiated, with swollen margins, entire to crenate or sublobate around the apothecia, often variable within one thallus upper surface: dark olive-green, blue-gray or brown-black, dull or somewhat glossy, smooth to rugose-verrucose Apothecia: often numerous and crowded, innate to appressed, sometimes sessile with constricted base, 1-3(-4) mm broad disc: plane to convex, sometimes concave, light or dark red to red-brown, smooth, dull or slightly glossy, epruinose thalline margin: thick, entire to verrucose or lobulate, finally receding proper exciple: thin, centrally up to 40 µm high, marginally often thicker, euthyplectenchymatous or rarely subparaplectenchymatous hymenium: hyaline, 90-120 µm tall asci: clavate, (2-)4-spored ascospores: ovoid, ellipsoid, subovoid, ends usually obtuse, eumuriform or submuriform, (20-)26-34(-40) x (8.5-)10-15(-17) µm Pycnidia: immersed to prominent, especially on apothecial margin, pale conidia: bacilliform or with slightly swollen ends, 4.5-6 x 1-1.5(-1.8) µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on damp, ±calciferous clay or sandy soils, also in disturbed habitats at low elevations World distribution: Europe, North America, Africa, and China Sonoran distribution: southern California. Notes: Collema limosum is very characteristic with its 4-spored asci, its large apothecia (up to 2 mm wide) and in having a poorly developed, membrane-like thallus that lacks distinct lobes.