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DescriptionThallus: foliose, multi-lobed, attached by few to several holdfasts with 5-12 mm wide lobes; upper surface: gray with epinecral layer consisting of air-filled hyphae; upper cortex: 60-120 µm thick, hyaline with the outermost part (ca 10 µm) brownish; medulla: 70-220 µm thick, turning reddish or reddish brown with Melzer's iodine; lower cortex: 40-70 µm thick with the outermost part (c. 10 µm) light brown to brown; lower surface: light brown, usually reticulate at least partly; Perithecia: obpyriform to globose, 210-320 µm high and 180-300 µm wide, with hyaline exciple which is brown in the uppermost part; asci: clavate or cylindrical, 8-spored; ascospores: simple, hyaline, (8.5)10-13.5(-16) x (4.5-)5.5-7(-8.5) µm; Pycnidia: not found in Sonoran material, elsewhere rare, immersed, ostiolum similar to that of the perithecium; conidia: bacilliform, 5-6 x 1 µm; Spot tests: all negative; Secondary metabolites: none detected.; Substrate and ecology: rocks at higher elevations; World distribution: bipolar, arctic or at higher altitudes; Sonoran distribution: only known from the San Francisco Peaks, Arizona at 3550 m.; Notes: Dermatocarpon polyphyllizum is an arctic species with its main distribution at high elevations. It shows polymorphism concerning the lobe-number, there are present both multilobed and single-lobed specimens. The Sonoran specimen was, however, multilobed.