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DescriptionThallus: foliose, adnate to loosely adnate, 4-12 cm in diam., irregularly lobate; lobes: subirregular, elongate, plane to subconvex, often black rimmed, separate, contiguous to somewhat imbricate, (0.5-)1-3 mm wide, rarely lobulate; apices: subrotund to subtruncate, smooth to crenate, eciliate; upper surface: yellow-green, smooth, shiny, epruinose and emaculate, moderately to densely isidiate; isidia: initially globose, soon becoming cylindrical, simple to coralloid branched, 0.06-0.2 mm in diam., 0.1-1 mm tall; tips: syncorticate, dull brown to black; soralia and pustulae absent; medulla: white, with continuous algal layer; lower surface: black, plane, moderately to densely rhizinate; rhizines: black, simple to furcate, 0.2-0.6 mm long; Apothecia: rare, substipitate, 2-8 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown, epruinose; margin isidiate; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, 9-10 x 5-6 µm; Pycnidia: rare, immersed; conidia: bifusiform, 6-7 x 1 µm; 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), constictic, cryptostictic and norstictic acids (all minor), connorstictic acid (trace), and sometimes hyposalazinic acid (trace).; Substrate and ecology: on acidic rocks, rarely on wood, often in open, arid habitats but also in more shaded, forested habitats; World distribution: Europe, Africa, North and South America; Sonoran distribution: occasional at lower elevations in Arizona, California, Baja California, and Chihuahua.; Note: Desert populations of X. conspersa generally have more narrow, adnate lobes than populations from eastern North America or Europe. Within the stictic acid containing populations with black lower sufaces in the Sonoran region, one can often find specimens with either cylindrical, non-erumpent isidia or globose to subglobose isidia that often become erumpent. The name X. conspersa is restricted to the former specimens; whereas, X. amableana is applied to the latter collections. These species also exhibit chemical differences. Whereas constictic acid is a significant (submajor) metabolite of X. conspersa, it is absent in X. amableana, whereas menegazziaic acid (minor) present in X. amableana is absent in X. conspersa.