Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: foliose, c. circular in outline, lobate lobes: usually subirregular; tips: usually subrotund, eciliate upper surface: pale yellow green to whitish or gray, smooth, plane to rugulose, dull, usually strongly pruinose, with or without soredia, emaculate; pseudocyphellae: absent upper cortex: palisade plectenchymatous, pored epicortex medulla: white, cell walls containing Cetraria-type lichenan photobionts: primary one a Trebouxia, secondary photobiont absent lower surface: ivory white to light brown or purplish black, velvety, frequently with a gray margin (like mouse fur), attachment by sparse, simple rhizines, cyphellae, pseudocyphellae and tomentum absent Ascomata: apothecial, imperforate, laminal on thallus, orbicular, cup-shaped, sessile, margin prominent with thalloid rim; exciple gray or hyaline, hypothecium hyaline, epithecium brown or brownish yellow asci: lecanoral, wall layers apex thickened, apex amyloid, with wide, axial body divergent towards apex ascospores: c. 8 per ascus, simple, ellipsoid; 10-12 µm long, 4-6 µm wide; wall thin, hyaline Conidiomata: absent or present, pycnidial, laminal, immersed conidia: bifusiform, 6 x c. 1 µm Secondary metabolites: upper cortex with usnic acid and atranorin and chloroatranorin; medulla with an orcinol depsidones and (higher) aliphatic acids Geography: throughout arctic and northern boreal regions of the Northern Hemisphere and extending southwards in high montane areas Substrate: mostly on non-calciferous rocks. Notes: Among the Parmelia generic segregates, Arctoparmelia is most similar to the southern hemispheric Psiloparmelia in cortical chemistry and color of the lobe tips and the lower side, but the later genus has only a rudimentary epicortex, isolichenan in the cell walls and lacks rhizines. Among the yellow-green, non-pseudocyphellate parmelioids occurring in the Sonoran region, Flavoparmelia has broader lobes, larger spores, isolichenan in the cell walls and brown lobe tips on the lower side and the ubiquitous genus Xanthoparmelia has a shiny, epruinose upper surface, Xanthoparmelia-type lichenan in the cell walls, shiny brown or black lobe tips on the lower side, only usnic acid in the upper cortex and a far more complex medullary chemistry.