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Leptogium arsenei Sierk
Family: Collemataceae
Leptogium arsenei image
Stephen Sharnoff  
Thallus: foliose, 2-5 cm in diam., adnate, subdichotomously to irregularly lobate lobes: irregular, elongate, +plane to somewhat wrinkled, separate, 3-10 mm wide, 200-350(-500) µm thick; apices: rotund, entire to irregularly cut and isidiate, occasionally upturned upper surface: usually medium gray but sometimes brownish gray, usually dull, wrinkled especially longitudinally isidia: usually dense, laminal to marginal, granular initially, becoming cylindrical to sometimes lobulate, usually simple, concolorous with the thallus or darker internal anatomy: with upper and lower cortices consisting of a single layer of irregularly isodiametrical cells 2-5 µm in diam., internally with loosely interwoven chains of Nostoc and hyphae lower surface: pale to medium gray, wrinkled longitudinally, with scattered tufts of white hairs Apothecia: not observed Pycnidia: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: particularly common on acidic rocks and occasionally found at the base of trees World distribution: western to rarely central North America Sonoran distribution: one of the most common Leptogiums on rock in central and southeastern Arizona, California, Baja California, Sonora and Chihuahua. Notes: Darker thalli of L. arsenei are superficially rather like a Collema, due to its thick gelatinous thallus, but it has a proper cortex. Its granular isidia make it a distinctive species.