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 appressed, large, 8-15(-30) cm, straw-yellow, lobate lobes: sublinear to subirregular, 4-12(-16) mm wide, plane, contiguous; apices: broadly rounded upper surface: greenish-yellow to yellow-green, turning a dark buff or yellow-brown with age in the herbarium, smooth (especially at the margins) to weakly wrinkled, rarely weakly ridged-reticulate, sometimes with white maculae pseudocyphellae: white, common to occasional, punctiform to effigurate, occasionally merging, up to 0.3 mm wide asexual propagules: none medulla: white with a continuous algal layer lower surface: pale tan to buff, often darker near the margins, smooth to commonly finely wrinkled; rhizines: simple to rarely branching, short, concolorous with the lower surface or darkening, usually absent in a broad zone along the margins (as in Parmotrema spp.) Apothecia: common (but may be absent), lecanorine, sessile to substipitate and up to 6 mm in diam.; disc: red-brown; exciple: often pseudocyphellate, usually continuous, smooth, entire to slightly undulating; epithecium: pale yellow-brown; hymenium: hyaline; hypothecium: hyaline asci: Lecanora-type, 8-spored ascospores: simple, hyaline, broadly ovoid to ellipsoid, 8-15.5 x 6-10 µm Pycnidia: black, usually common, laminal and concentrated toward the margins conidia: bifusiform or appearing filiform, 5-8 x c. 1 µm Spot tests: upper cortex K+ yellowish, KC-, C-, P-; medulla C+ red, KC+ red, K-, P- Secondary metabolites: upper cortex with usnic acid (minor); medulla with lecanoric acid (major), 5-chlorolecanoric acid (+ minor or usually trace). Substrate and ecology: on bark of both hardwoods (Acer, Prunus, Quercus, Salix) and conifers (Pinus, Pseudotsuga) from 1370-2700 m World and Sonoran distribution: endemic in the oak-pine forests of southeastern Arizona and at higher elevations of Chihuahua and Sonora, Mexico. Notes: Both the thallus lobes and the whole thalli of F. darrowii are usually larger than those of F. praesignis and with practice can usually be recognized in the field without checking the lower surface. The specific epithet for this species has been spelled in a number of ways: F. | darrowi, F. darrowii, F. darrovii and F. darrovi. The taxon was originally described as Parmelia darrowi (after the original collector, Robert Darrow). According to article | 60.11. of the Botanical Code this original spelling constitutes an orthographical error and the species name must be corrected to F. darrowii.