Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: foliose, adnate to loosely adnate, 5-10 cm in diam., irregularly lobate; lobes: subirregular, short to elongate, plane but sometimes with upturned lobe tips, separate, contiguous or more usually imbricate, 1.5-3 mm wide; apices: subrotund to subtruncate, smooth to crenate, often brown to blackish brown marginally, eciliate; often becoming lobulate centrally and/or marginally; lobulae: plane to convex, irregularly branched, 0.05-1 mm wide; upper surface: dark yellow-green to bluish yellow-green, smooth, shiny or dull, epruinose and rarely white maculate, without isidia, soralia or pustulae; medulla: white, with continuous algal layer; lower surface: pale brown, plane, moderately to densely rhizinate; rhizines: pale brown, simple, 0.5-1 mm long; Apothecia: common, substipitate, 3-15 mm wide, laminal on thallus; disc: cinnamon-brown to dark brown; margin: smooth, pruina absent; asci: clavate, 8-spored; ascospores: hyaline, simple, ellipsoid, 7-9 x 4-5 μm; Pycnidia: common, immersed; conidia: bifusiform, 4-6 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 usually norstictic and protocetraric acids (both trace).

Substrate and ecology: on acidic rocks, often in open, arid habitats; World distribution: very common at intermediate elevations in western North America and Hawaii; Sonoran distribution: common at intermediate elevations in Arizona, southern California and Sonora and extending to open, coastal habitats.

Note: Earlier reports (Nash 1974b, Hale 1979) usually referred to this species as X. taractica in the Southwest, but the latter species is now treated as a Southern Hemispheric species that is larger, more loosely adnate and typically occurs on soil (Nash et al. 1986). In contrast to the very common X. lineola (Berry) Hale, X. coloradoënsis is lobulate. The lobulae are very loose and do not form a mat found in some other species whereas the main lobes are quite adnate.

Global occurrence: Americas – North America (incl Mexico) | Oceania – Pacific Islands (Melanesia, Micronesia, Polynesia) | Arctic.  Substrate: rock – siliceous, siliciferous, acidic | rock, stones, pebbles – unspecified.  Life habit: lichenized (mutualistic with algal photobionts).  Thallus: foliose (foliaceous), leaf-like; [th] upper surface: yellow(ish) green | green(ish) yellow; [th upper surface]: epruinose; [th marginal and upper surface] specific structures: absent; [th] morphol substructures (eg areoles, lobes, branches) width [mm]: (low) 1.5 (high) 3.0; [th] morphol substructures (eg areoles, squamules): distantly discontiguous; [th] morphol substructures (eg areoles, lobes, branches) upper surface: smooth, plane | maculate; [th] lower surface: brown(ish) (if pale: fawn, tan; if mid: cinnamon); [th lower surface] specific structures: present; [th lower surface] rhizines, rhizoid structures: present; [th lower surface] rhizines, rhizinoid structures: unbranched, simple.  Ascomata: absent | present; ascoma: apothecial, apothecioid – hymenial; ascoma [mm]: (low) 3.0 (high) 15.0; ascoma: subpedicellate, substipitate, subpedunculate, substalked; [ascm, if apoth] disc, mazaedium: plane, flat, flattened, expanded; [ascm, if apoth] disc, mazaedium: brown(ish) (if pale: fawn, tan; if mid: cinnamon); [ascm, if apoth] disc, mazaedium: epruinose; [ascm, if apoth] margin surface; [if perith] periostiolar area, ostiole, involucrellum: yellow(ish) green | green(ish) yellow; [ascm, if apoth] margin excipular photobionts: present | abundant; [ascm, if apoth] subhymenial layers, hypothecium; [if perith] basal excipulum: hyaline, colourless; [ascm] paraphyses/-oids: present; [ascm] epihymenium, epithecium: brown(ish) (if pale: fawn, tan; if mid: cinnamon).  Asci: lecanoralean; [asc] tholus: thickened; [asc] tholus amyloidity (iodine reaction): present; [asc] tholus amyloidity pattern: amyloid with widening axial body towards the apex (= Lecanora-, Parmelia-, Rinodina-types etc).  Ascospores: (median) 8.0; [asp] shape: ellipsoidal; [asp] length [µm]: (low) 7.0 (high) 9.0; [asp] width [µm]: (low) 4.0 (high) 5.0; [asp] septa: absent – spore lumen unilocular, monolocular; [asp] pigmentation: hyaline, colourless; [asp] perispore, epispore: not apparent.  Conidiomata: absent | present.  Conidia: bifusiform; [co] length [µm]: (low) 4.0 (high) 6.0.  Secondary metabolites: present, consalazinic acid | norstictic acid | protocetraric acid | salazinic acid | usnic acid.  Primary photobiont: present, chlorophytaceous – trebouxiaceous, chlorococcoid. Secondary photobionts (eg in cephalodia): absent.