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Psora russellii (Tuck.) A. Schneider
Family: Psoraceae
[Biatora russellii Tuck.,  more]
Psora russellii image
Joselyn Fenstermacher  
Squamules: up to 6 mm wide, rounded, adnate and dispersed to adjacent or imbricate, usually weakly to strongly concave upper surface: medium to castaneous brown, dull or shiny, epruinose or partly pruinose, smooth or sparingly fissured margin: concolorous with upper side or white, down-turned or straight, entire or lobed upper cortex: up to 60-180 µm thick, composed of thin-walled hyphae with round lumina, containing crystals of lichen substances and calcium oxalate medulla: containing lichen substances and calcium oxalate lower cortex: of mainly periclinally oriented hyphae, not containing calcium oxalate lower surface: white to medium brown Apothecia: up to 1 mm diam., laminal-submarginal, immarginate, or marginate when young and later becoming immarginate, medium brown, epruinose or yellow pruinose ascospores: ellipsoid, 11-15 x 5-8 µm Pycnidia: unknown Spot tests: upper cortex and medulla K+ red, C-, KC-, P+ orange Secondary metabolites: norstictic acid and sometimes trace of gyrophoric acid. Substrate and ecology: on soil or in crevices of rock in open habitats, mainly in deserts, rare in Californian coastal scrub and pinyon-juniper woodland, up to 1810 m World distribution: North America Sonoran distribution: rather common in Arizona, California, Baja California, and Sonora.