Thallus: foliose but almost areolate centrally, tightly adnate, 5-7 cm in diam., irregularly lobate; lobes: sublinear, elongate, plane to subconvex, separate to contiguous or subimbricate, 0.5-1 mm wide, not lobulate; apices: subrotund to subtruncate, smooth to crenate, eciliate; upper surface: yellow-green but darkening with age, smooth, dull to slightly shiny, epruinose and emaculate, without soralia, isidia, or pustulae; medulla: white, with continuous algal layer; lower surface: pale brown centrally to darker brown peripherally, plane, moderately to densely rhizinate; rhizines: brown, simple, 0.1-0.2 mm long; Apothecia: common, sessile to substipitate, 1-4 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, 9-11 x 4-6 µm; Pycnidia: common, immersed; conidia: bifusiform, 6-7 x 0.5 µm; Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ yellow becoming dark red, C-, KC-, P+ red; Secondary metabolites: upper cortex with usnic acid (major) and +atranorin (minor); medulla with norstictic acid (major) and connorstictic acid (minor) and +salazinic acid (minor).; Substrate and ecology: on acidic rocks, often in open, arid habitats; World distribution: Australia and SW North America; Sonoran distribution: rare at lower elevations in Sonora.; Notes: This is the first report of X. parvoclystoides for North America. This species is characterized by its small, tightly adnate, ±subcrustose thalli which often form areolae in older parts of the thallus, the brown lower surface and the presence of the norstictic acid chemosyndrome in the medulla. Xanthoparmelia parvoclystoides is similar to X. californica but differs in having a much more tightly adnate thallus that is ±areolate centrally, and in having narrower lobes (0.5-1 mm vs. 0.8-2 mm wide). Morphologically X. parvoclystoides is similar to X. neorimalis but differs in containing norstictic acid instead of salazinic acid as the major secondary metabolite.
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