Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: foliose, adnate, 4-8 cm in diam., dichotomously lobate lobes: sublinear to subirregular, elongate, plane to subconvex, separate, contiguous to slightly imbricate, black-rimmed, 0.4-1 mm wide, not lobulate; apices: subtruncate to subrotund, smooth to crenate, eciliate upper surface: dark yellow-green, smooth, shiny, epruinose and emaculate, without soralia, isidia, or pustulae medulla: white, with continuous algal layer lower surface: black, plane, sparsely to moderately rhizinate; rhizines: black, simple, 0.3-0.5 mm long Apothecia: common, sub-stipitate, 3-7 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 9-10 x 5-6 µm Pycnidia: common, immersed conidia: bifusiform, 6-7 x 1 µm Spot tests: upper cortex K-, C-, KC-, P-, medulla K-, C-, KC-, P+ yellow Secondary metabolites: upper cortex with usnic acid (major); medulla with psoromic acid (major) and 2'-O-demethylpsoromic acid (minor). Substrate and ecology: on acidic rocks, often in open, arid habitats World distribution: most common in southwestern North America and also reported from Argentina in South America Sonoran distribution: common at lower elevations in Arizona and Sonora. Notes: Unlike most of the other non-isidiate species with black lower surfaces, X. huachucensis is fairly narrow lobed. Its medullary chemistry (psoromic acid major) separates it from the somewhat similar X. planilobata, which has stictic acid as the major secondary metabolite.