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

Thallus: foliose, tightly adnate to adnate, 3-6 cm in diam., irregularly lobate lobes: sublinear, elongate, plane, separate, contiguous to somewhat imbricate, 0.7-1.5 mm wide, developing short lobulae centrally; main apices: subrotund to subtruncate, smooth to crenate, eciliate upper surface: dark yellow-green, smooth, shiny, epruinose and emaculate, without isidia, soralia or pustulae medulla: white, with continuous algal layer lower surface: pale to dark brown, plane, moderately rhizinate; rhizines: pale to dark brown, simple, 0.2-0.5 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: hyaline, simple, ellipsoid, 9-11 x 5-6 µm Pycnidia: common, immersed conidia: bifusiform, 5-7 x 0.5 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P- Secondary metabolites: upper cortex with usnic acid (major); medulla with lichesterinic acid (major) and protolichesterinic acid (minor or trace). Substrate and ecology: on acidic rock, often in open, woodland habitats World distribution: intermountain areas of western North America Sonoran distribution: occasional at intermediate elevations in pinyon-juniper and mixed conifer communities in central Arizona. Note: Although authentic material of X. montanensis is known from the Sonoran region, collections labelled as such from southern California proved to be X. oleosa. Both species contain fatty acids in the medulla and are best distinguished by thin layer chromatography. In addition, X. montanensis has somewhat larger spores than X. oleosa (9-11 x 5-6 µm vs. 7-8 x 4-5 µm).