Thallus: foliose to subcrustose, adnate to tightly adnate, 4-7 cm in diam., irregularly lobate lobes: sublinear to subirregular, elongate, plane to subconvex, separate and contiguous, 0.8-2 mm wide, densely lobulate; lobulae sublinear to sublinear-elongate or vermiform, subdichotomously to palmately branched, 0.1-0.2 mm wide, sometimes dominating the thallus; apices: subrotund to subtruncate, smooth to crenate, eciliate upper surface: yellow to yellow-green, smooth but becoming strongly rugose and cracked with age, ±areolate, dull to slightly shiny, epruinose and emaculate, without soralia, isidia, or pustulae medulla: white, with continuous algal layer lower surface: pale to medium brown, dark brown or black near the apices, plane, moderately rhizinate; rhizines: pale brown, simple, 0.1-0.3 mm long Apothecia: common, substipitate, 0.5-2 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 11-13 x 5-7 µm Pycnidia: common, immersed conidia: bifusiform, 5-6 x 1 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P+ red Secondary metabolites: upper cortex with usnic acid (major); medulla with fumarprotocetraric acid (major), protocetraric acid (minor), confumarprotocetraric acid (minor). Substrate and ecology: on acidic rocks World distribution: North America Sonoran distribution: Arizona and Baja California. Notes: Xanthoparmelia lobulatella is characterized by the adnate to tightly adnate, foliose to subcrustose thalli dominated by minute lobules 0.1-0.2 mm wide, its pale lower surface and the medullary fumarprotocetraric acid. The primary lobes resemble those of X. novomexicana, a species with identical medullary chemistry. However, X. novomexicana is elobulate and has smaller ascospores (10-11 x 4-5 µm vs. 11-13 x 5-7 µm). The other subcrustose species in the Sonoran region usually have isidia (although one is sorediate), and all have a different suite of secondary metabolites.