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, 4-6 cm in diam., dichotomously lobate lobes: sublinear, elongate, plane to subconvex, separate and contiguous, 0.4-0.8 mm wide, not lobulate; apices: subtruncate, black rimmed, smooth to crenate, eciliate upper surface: light yellow-green but darkening with age, smooth but becoming transversely cracked, shiny, epruinose and emaculate, moderately to densely isidiate isidia: cylindrical, breaking off easily, unbranched to sparsely branched, 0.05-0.07 mm in diam., 0.1-0.4 mm tall; tips: syncorticate, dark brown, often erumpent but not sorediate; soralia and pustulae absent medulla: white, with continuous algal layer lower surface: pale to dark brown, plane, shiny, moderately rhizinate; rhizines: dark brown, simple, 0.1-0.2 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) and constictic and norstictic acids (minor), and cryptostictic and peristictic acids (both trace). Substrate and ecology: on acidic rocks, often in open, subtropical to tropical habitats World distribution: central and southern Africa, the Caribbean, northern South America, Central America to Mexico Sonoran distribution: occasional at low to intermediate elevations in Sinaloa and Sonora. Notes: This tightly adnate almost subcrustose species is distinguished by the presence of isidia, the brown lower surface and the presence of the stictic acid chemosyndrome in the medulla. In the Sonoran region X. neopropaguloides is most common in subtropical to thorn forest habitats.