Life habit: lichenized, lichenicolous when young Thallus: crustose, mostly poorly developed, forming patches mostly to 3(-4) cm across, moderately thick, composed of loose clusters of discrete verrucae or areoles areoles: often distinctly separated from one another and then fastened at the base to a dark prothallus, convex to hemispherical or +globose, 0.2-0.6(-0.8) mm in diam., smaller areoles sometimes arising from within the areoles of the Rhizocarpon surface: chestnut-brown, copper brown or duller brown to dark brown, glossy, with blackened edges but lacking thallospores cortex: phenocortical, 20-30 µm thick, with a brown upper cell layer, with an epinecral layer c. 10 µm thick Apothecia: usually numerous, at first immersed and perithecia-like, eventually +sessile, 0.2-0.6(-1.2) mm in diam. disc: chestnut brown to brown, dark red-brown, or dark brown, shiny, plane to convex margin: thin, level with disc, entire, soon disappearing amphithecium: with an eucortical cortex overlain by a gelatinous layer, with a distinct medulla filled with algal cells exciple: thin, concolorous with the thallus externally, hyaline internally, soon disappearing epihymenium: +olive-brown hymenium: hyaline, 45-50 µm tall, I+ blue; paraphyses rather thick, tightly coherent, pale brown at tips; hypothecium: hyaline asci: clavate, 8-spored ascospores: hyaline, simple, oblong-ellipsoid to oblong, blunt at both ends, 8-13(15) x (3.7-)5-7 µm Pycnidia: rare, immersed, dark above conidia: hyaline, filiform, curved, very thin, 18-20(-30) µm long Spot tests: cortex of thallus and apothecia (in sections) K+ yellow to red, C-, KC-, P+ yellow or orange, UV- Secondary metabolites: norstictic acid, traces of unknowns, including a fatty acid (rangiformic?); sometimes also with psoromic acid from the Rhizocarpon. Substrate and ecology: initially parasitic on yellow species of Rhizocarpon (especially R. geographicum s. lato and R. lecanorinum), later autonomous, over hard acidic (e.g., granite, gneiss, or occasionally sandstone), often on boulders in open fields, at moderate elevations World distribution: Europe and North America Sonoran distribution: Arizona at 2500-2750 m. Notes: Protoparmelia atriseda differs from P. nephaea, with which it has often been confused, by its thallus forming smaller patches (mostly under 4 cm across), its close association with and perhaps and initial parasitism on yellow species of Rhizocarpon (Poelt and Leuckert 1991), its lack of thallospores, its K+ yellow to red (norstictic acid), and its discs being chestnut brown rather than black. It represents the type species of Protoparmelia sect. Phaeonora Poelt & Leuckert, mainly based on its filiform conidia and the regular occurrence of norstictic acid.