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, 2-7 cm in diam., dichotomously lobate lobes: subirregular to sublinear, elongate, plane to subconvex, separate, contiguous to somewhat imbricate, 0.8-1.5 mm wide, not lobulate; apices: subrotund, smooth to crenate, eciliate upper surface: light yellow-green, smooth, shiny, epruinose and emaculate, moderately isidiate isidia: abundant, usually globose but becoming subcylindrical, mostly unbranched, 0.08-0.15 mm in diam., 0.1-0.2(-0.5) mm tall; tips: epicorticate, pale brown to black, often erumpent but not sorediate; soralia and pustulae absent medulla: white, with continuous algal layer lower surface: pale brown, plane, moderately rhizinate; rhizines: pale brown, simple, 0.2-0.4 mm long Apothecia: not observed Pycnidia: not observed Spot tests: upper cortex K+yellow to orange, C-, KC-, P+ orange; medulla K+ yellow becoming dark red, C-, KC-, P+ orange Secondary metabolites: upper cortex with usnic acid (major); medulla with stictic acid (major) constictic, cryptostictic and norstictic acids (minor), and peristictic and connorstictic acids (trace). Substrate and ecology: on acidic rocks, often in open habitats World distribution: predominately subtropical to tropical parts of South America and extending into Mexico Sonoran distribution: occasionally at lower elevation in Arizona, southern California, Baja California, Chihuahua, and Sonora. Note: Previously X. subplittii has been confused with X. plittii and the distinguishing features of these two species are discussed under the latter.