Thallus: foliose, adnate to loosely adnate, appressed, 2-8 (-12) cm diam., rosette-forming, lobate lobes: ± radiating, irregular, 0.5-1.5 (-2.5) mm wide, linear to rounded, discrete or contiguous and imbricate; margins wavy to somewhat dissected, apices subrotund, without cilia upper surface: ashy whitish gray (becoming cream-colored in herbarium) to greenish gray, sometimes becoming brownish, dull and slightly arachnoid or pruinose under strong magnification (x 50), becoming smooth and somewhat shiny toward periphery, sometimes wrinkled or shallowly pitted towards center; without pseudocyphellae or maculae; with or without isidia (occasionally also becoming sorediate) upper cortex: paraplectenchymatous, 10-20 micrometer thick, covered by a pored epicortex medulla: white, forming an irregular layer; cell walls containing Cetraria-type lichenan (I+ blue) photobiont: primary one a chlorococcoid alga (Trebouxia or Myrmecia), secondary photobiont absent lower cortex: similar in thickness and structure to upper one lower surface: white to light brown; rhizines: scattered and sparse to moderately dense or dense, usually rather short, concolorous with lower surface, simple, tufted or not, extending to the margins but rarely on the margins themselves Ascomata: apothecial, mostly laminal, rather large, to 7 (-12) mm diam., adnate to sessile or short-pedicellate,with a thalline margin concolorous with thallus; disc: round, ± concave, imperforate, light brownish yellow to yellowish brown or dark brown; true exciple: gray or hyaline; epihymenium: brown or ochraceous-yellowish; ostiolar filaments absent; hymenium: hyaline, with simple or rarely branched paraphyses; hypothecium: hyaline or tinted brown asci: clavate, Lecanora-type, unitunicate; tholus I+ blue, 8-spored ascospores: ellipsoid, obtuse at the poles, straight, simple, 4-6 (-9) x 3-4 (-6) micrometer, wall hyaline, thin, smooth, without distinct endospore thickening, I- Conidiomata: pycnidial, laminal and marginal, to 0.2 mm diam., emergent, globose, black; conidiophores Psora-type conidia: ampulliform or occasionally bifusiform (3-) 4-5 (-6) x (0.5-) 1 (-1.5) micrometer Secondary metabolites: cortex atranorin and chloroatranorin; medulla with ß-orcinol depsides or orcinol depside Geography: circumpolar, temperate-boreal in the Northern Hemisphere; also known from Australia Substrate: usually on bark or wood of conifers. Notes: It is distinguished from most other parmelioid genera by its conidiophore type, and by its narrow, often strap-shaped, and ± appressed lobes. It was segregated from Parmeliopsis on the basis of its emergent and partly marginal pycnidia, its short, ellipsoid spores and its short, lageniform to bifusiform conidia; Imshaugia is also distinguished from that genus by its consistently pale lower surface, lack of soredia (at least without first developing isidia), content of lichenan rather than isolichenan in the cell walls, and presence of thamnolic acid (P+) rather than divaricatic acid (P-) in the medulla. Nomenclatural and taxonomic history of Parmeliopsis (syn. Foraminella) and Imshauga is complex and has led to incorrect or misleading information in the literature (Hinds 1999). Both of the species occurring in the Sonoran Region exhibit extremes of morphology and color as annotated by Meyer.