Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: foliose, loosely adnate, 15-10 cm in diam., irregularly lobate lobes: sublinear, elongate, plane to subconvex, separate and loosely imbricate, 1-3 mm wide; apices: subrotund to subtruncate, smooth to crenate, eciliate, becoming densely lobulate centrally lobules: strongly convex to convolute but with flattened lobe tips, di- or trichotomously branched, 0.2-0.7(-1) mm wide, subascending black-rimmed upper surface: yellow to yellow-green, smooth, shiny or dull, epruinose and weakly white maculate, without soralia, isidia, or pustulae medulla: white, with continuous algal layer lower surface: ivory to pale brown, sometimes canaliculated particularly within the lobulae, shiny, moderately rhizinate; rhizines: brown to brownish black, simple to tufted or rarely branched, often extending beyond lobe margin, 0.3-0.6 mm long Apothecia: common, substipitate, 2-6 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown, concave; margin: smooth, pruina absent asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 7-9.5 x 4.5-6 µm Pycnidia: common, immersed conidia: bifusiform, 5-6 x 0.5 µm Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ yellow to dark red, C-, KC-, P+ orange Secondary metabolites: upper cortex with usnic acid (major); medulla with salazinic acid (major) consalazinic acid (minor) and sometimes norstictic acid (trace). Substrate and ecology: on acidic pebbles and adjacent soil, often in open, coastal habitats or mid-elevation woodlands World and Sonoran distribution: locally common at intermediate elevations in the Sierra Madre Occidental of Chihuahua and coastal areas of southern California and Baja California. Notes: As originally described X. commonii was documented as a locally common species occurring in the Sierra Madre Occidental but we now consider that it also includes the more revolute-lobed population of salazinic acid containing specimens occurring on soil in Pacific coastal areas.