Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: foliose, loosely adnate to adnate, 5-8 cm in diam., irregularly lobate lobes: sublinear, elongate, plane, separate, contiguous to somewhat imbricate, 1-2.5 mm wide, not lobulate; apices: subrotund to subtruncate, smooth to crenate, eciliate upper surface: light yellow-green, smooth, shiny, epruinose and emaculate, without isidia, soralia and pustulae medulla: white, with continuous algal layer lower surface: pale to dark brown, plane, moderately rhizinate; rhizines: pale to dark brown, simple, 0.5-1 mm long Apothecia: common, substipitate, 1-3 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent asci: clavate, 8-spored ascospores: not observed Pycnidia: common, immersed conidia: bifusiform, 5-7 x 0.5 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P+ orange Secondary metabolites: upper cortex with usnic acid, medulla with fumarprotocetraric acid (major), physodalic and constipatic acids (both minor), protocetraric acid (trace) and sometimes protoconstipatic acid (trace). Substrate and ecology: on acidic rocks, often in open habitats World distribution: predominately in eastern North America in the southern Appalachian Mountains to central Mexico Sonoran distribution: occasionally at intermediate elevation in Arizona and Chihuahua. Note: The original description of X. monticola mentioned the occurrence of stictic acid, but this was apparently due to a contaminant. This species is distinguished by the medullary fumarprotocetraric acid, the brown lower surface and the loosely to moderately adnate, foliose thallus. Xanthoparmelia novomexicana is similar, but has tightly adnate thalli and lacks physodalic and constipatic acids present in X. monticola.