Thallus: foliose, tightly adnate to adnate, 3-5 cm in diam., irregularly lobate lobes: subirregular, short, plane to sub-convex, separate and contiguous to somewhat imbricate, 0.8-2 mm wide, not lobulate; apices: subrotund, smooth to crenate, eciliate upper surface: yellow-green, smooth, dull to somewhat shiny, epruinose and emaculate, abundantly isidiate isidia: initially globose, soon becoming cylindrical to irregularly inflated, 0.1-0.2 mm in diam., 0.1-0.8 mm tall; tips: epicorticate, dull brown, sometimes erumpent; soralia and pustulae absent medulla: white, with continuous algal layer lower surface: black, plane, sparsely rhizinate; rhizines: black, simple, 0.2-0.4 mm long Apothecia: frequent, 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: not observed Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ yellow to orange, C-, KC-, P+ orange Secondary metabolites: upper cortex with usnic acid (major); medulla with stictic acid (major), menegazziaic, cryptostictic and norstictic acids (minor), and peristictic and substictic acids (trace). Substrate and ecology: on acidic rocks, often in open, arid habitats World and Sonoran distribution: Arizona, Isla Guadalupe, Baja California, Baja California Sur, Sonora and Chihuahua. Notes: Heretofore X. conspersa was the only isidiate species with a black lower cortex and stictic acid as the major metabolite recognized as occurring in the Southwest (Nash 1974). However, X. conspersa comprises specimens with strictly cylindrical isidia (Hale 1990); whereas specimens with at least initially globose, often erumpent isidia are accomodated in X. amableana. Unlike the southern South American X. wrightiana T.H. Nash, Elix & J. Johnst., the isidia do not become subsorediate at maturity.