Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: small-squamulose to granulose, squamules: up to 1 mm broad, upper surface: shiny yellow-brown to brown with interspersed dark bluegreen granules (containing Nostoc, i.e. cephalodia) upper cortex: paraplectenchymatous, 20-30 µm medulla: composed of loosely reticulate hyphae cephalodia: frequent, dark purple brown, granular to coralloid branched, occurring singly or in clusters (often under the apothecia) up to 0.8 mm wide, corticated by one or two rows of cells lower cortex: paraplectenchymatous, 30-40 µm thick Apothecia: small, up to 2 mm diam., with granular thalline margin; discs: brown with concolorous margin or dark brown with a lighter brown margin, flat; hymenium: I+ dark blue, 95-120 µm high; hypothecium: 20-25 (-50) µm thick including ascogenous hyphae; subhymenium: varying thickness, frequently extending into a stipe of adglutinated hyphae with enlarged cells towards the base asci: each with an internal amyloid apical tubes, 8-spored ascospores: simple, colorless, ovoid with warted epispore, 19-24 x 7-12 µm Pycnidia: inconspicuous conidia: rod-shaped, 2-4 x 1 µm thick Spot tests: K-, C-, KC-, P- Secondary metabolites: thallus and apothecia with pannaric acid, porphyrilic acid methyl ester and a related unknown. Substrate and ecology: wet soils near snowbeds in arctic-alpine environment World distribution: widespread in arctic-alpine parts of the Northern Hemisphere Sonoran distribution: rare, only collected a few times in the high mountains (above 3000 m) in Arizona, where it has the southernmost known locality in North America. Notes: This taxon is separated from the similar P. hypnorum by its small flat apothecia and the shining brown, more granular thallus containing lichen metabolites. Psoroma tenue var. tenue, described from southern South America (Henssen and Renner 1981), has smaller lobes than P. tenue var. boreale and its cortex is less well developed.