Squamules: up to 4 mm diam., elongated, ascending, irregularly imbricate. Upper side: yellowish green to pale brownish green, becoming brown in the herbarium, dull to slightly shiny, epruinose or white pruinose towards the margin, usually with some fissures; margin: more brightly yellow, pruinose, more or less straight, entire to crenulate; underside: white to pale brown. Upper cortex: 110-150 μm thick, composed of thick-walled hyphae with mainly angular lumina, containing usnic acid. Medulla: frequently containing gyrophoric acid. Lower cortex: well developed, composed of anticlinally oriented hyphae with shortly cylindrical lumina and densely covered with calcium oxalate. Apothecia: up to 2 mm diam., attached laminally to the squamules, simple or compound, immarginate and strongly convex to hemispherical even when young, brownish black to black, dull, epruinose or more rarely faintly yellow to green pruinose. Ascospores: 9-14 x 5-7 μm. Pycnoconidia: 4-7 x 1 μm. Thallus chemistry: usnic acid and usually gyrophoric acid.
Psora rubiformis is easily distinguished by the ascending, yellowish green to pale brownish green squamules, and is the only species in the genus known to contain the yellow pigment usnic acid. The bright yellow P. hypotheja (southern South America) also forms ascending squamules, but the pigment is rhizocarpic acid. The lower cortex of P. rubiformis differs from that of all other species of the genus, except for P. nipponica and P. tenuifolia. The name P. rubiformis has been much misapplied, especially in North America, most frequently for P. himalayana, P. nipponica, and P. tuckermanii.
Circumpolar, arctic-alpine in the northern hemisphere.
The species is terricolous or grows in fissures in calciferous rock.
Psora hypotheja
