Life habit: lichenized Thallus: usually foliose but occasionally with an areolate center and appearing subcrustose, when growing free over soil appearing almost fruticose, continuous, irregularly or dichotomously lobate lobes: usually subirregular to sublinear, lobe tips usually subrotund but sometimes subtruncate, cilia absent upper surface: yellow-green to yellow (rarely green to blue-green) and sometimes darkening centrally, smooth, plane to subconvex or highly convex, smooth to rugulose, shiny or dull, usually emaculate but sometimes with well developed maculae, epruinose, often with isidia, more rarely sorediate or pustulate, pseudocyphellae absent upper cortex: pored epicortex, palisade plectenchymatous medulla: white, sometimes lower part pigmented, cell wall containing lichenan photobionts: primary one a chlorococcoid Trebouxia, secondary photobiont absent lower surface: black, medium to dark brown or tan to light reddish brown, plane to sometimes rugulose and rarely canaliculated, sparsely to densely rhizinate; rhizines: black or some shade of brown, almost always simple but occasionally furcated or tufted, rarely branched; cyphellae, pseudocyphellae and tomentum absent Ascomata: apothecial, absent or present, imperforate, laminal on thallus, orbicular, cup-shaped, sessile; margin: prominent, with thalloid rim, smooth or sometimes isidiate ascomata anatomy: exciple: gray or hyaline; epithecium: brown or brownish yellow; hypothecium: hyaline asci: lecanoral, wall layers apically thickened, amyloid, with wide, axial body divergent towards apex, 8-spored ascospores: simple, ellipsoid, 7-13 x 4-7 µm; wall: thin, hyaline Conidiomata: absent or present, pycnidial, laminal on thallus, immersed conidia: bacilliform, bifusiform or fusiform, 5-8 x 0.5-1 µm Secondary metabolites: upper cortex with usnic acid or atronorin; medulla with some combination of orcinol depsides, ß-orcinol depsides, ß-orcinol depsidones, (higher) aliphatic acids, antraquinones or other quinones, secalonic acids or amino acid derivatives Geography: cosmopolitan in at least partially open habitats outside of polar regions Substrate: mostly non-calciferous rock, sometimes on soil and rarely on tree bases when impregnated with dust. Notes: Currently Xanthoparmelia is the most species rich genus in the Parmeliaceae, a fact that reflects a wide array of secondary metabolite variation as well as considerable morphological variation, particularly with regards to the production of asexual propagules. Currently over 600 species are recognized, as the Southern Hemispheric genus Paraparmelia was recently synonymized with it (Elix 2003). Within this vast array of species, some similar morphologies with different chemistries are recognized as species within the genus, whereas in other genera (e.g. Niebla, this volume) a wider chemical circumspection of species is currently accepted. Support of the recognition of these species in Xanthoparmelia comes from investigations demonstrating habitat segregation in both low and intermediate elevation populations (Nash and Zavada 1977; Benedict and Nash 1990). In addition, chemosyndromic variation within Xanthoparmelia has been recognized (C. Culberson et al. 1979). Eventually, however, extensive molecular investigations will be required to help resolve appropriate phylogenetic clades within the group. Here the term "lobulae" is used in an equivalent manner to "lacinae" in other Xanthoparmelia treatments (e.g. Elix et al. 1986). Several species reported as occurring within the Sonoran region are no longer accepted. Xanthoparmelia barbatica (Elix) Egan, reported in (Egan 1982) and in Ryan et al. (2000), is now regarded as an Australian endemic, and the barbatic acid-containing species in North America is designated X. eganii (see below). Xanthoparmelia arsenana (Gyeln.) Hale was used as the narrow-lobed, very adnate Xanthoparmelia with a brown lower cortex, stictic acid and without isidia or soredia (Nash 1974b; Hale personal communication); however, Hale (1990) found that that the type of the species was a synonym of X. novomexicana due to its different chemistry (fumarprotocetraric acid). Herein that southwestern species is now treated as X. subcumberlandia Elix & T.H. Nash. Most but not all specimens reported as X. plittii (Gyeln.) Hale (Nash 1974b) have been transferred to X. subplittii Hale (see also below). Hale (1990) treated X. tinctina (Maheu & Gillet) Hale as strictly a European species, although he had previously agreed with the use of that name for our isidiate, salazinic acid species with a black lower cortex (Nash 1974b). Subsequently, we used the name X. australasica D.J. Galloway for this taxon, but that species is more loosely adnate, broadly lobed and has more narrow, taller isidia; consequently we reuse X. tinctina herein for most of the material based on comparisons with European material. The following reports from Nash et al. (1998) for Arizona have been redetermined as follows: X. australasica, as X. isidiigera; X. consociata, as X. pseudocongensis; and X. tegeta, as X. planilobata. The following reports from Ryan et al. (2000) for Mexico have been redetermined as follows: X. congensis and X. consociata, as X. pseudocongensis; X. diadeta, as X. substenophylloides; X. hypomelaena, as X. tuberculata; X. iniquita, as X. novomexicana; X. subconvoluta, as X. commonii or X. digitiformis; X. suberadicata, as X. neowyomingica; and X. wrightiana, as X. amableana.