Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: foliose, loosely attached, adnate to suberect, forming almost orbicular rosettes 1.5-4.5 (-6) cm broad, sometimes with long, narrow or broad, often erect lobes that give a fruticose impression lobes: short, 2-4 (-10) mm wide; dorsiventral, flat or occasionally slightly canaliculate, generally ascending, with raised lobe tips; branches: usually short; margins: becoming dissected; projections: not seen upper surface: intensely bright and deep yellow; foveolate, ridged and wrinkled (hand lens); soredia or isidia absent upper cortex: 15-40 (-50) µm thick with uppermost cells isiodiametric and 3-5 µm diam.; cells of the lower two layers: usually elongated, 3-7 x 3-5 µm medulla: yellow, hyphae 3-6 µm thick photobiont: cells (7-) 11-19 µm diam., in layer 10-22 µm thick lower cortex: similar to upper one lower surface: concolorous with upper one, wrinkled, strongly ridged; rhizines very sparse or absent Apothecia: common, 1-4 mm diam., laminal (to submarginal); thalline margin: crenulate; disc: dark brown asci: broadly clavate, 27-40 x 10-15 µm; tholus: with moderate amyloid reaction; 8-spored ascospores: subspherical, 5-6 x 4-5 µm Pycnidia: almost spherical, (90-) 110-120) x 100-110 (-120) µm, immersed, black, laminal, wall 10-20 µm, with c. three layers of isodiametric cells 2-3 µm diam., the uppermost parts black, closely connected to the cortex, lower parts with pale brown pigmentation conidia: citriform, 3-4 x 2 µm Spot tests: cortex K-, C-, KC+ yellowish, P-; medulla K+ yellowish, C-, KC-, P- Secondary metabolites: cortex with usnic acid; medulla with pinastric and vulpinic acids, rarely traces of other aromatic substances; sometimes also an unknown fatty acid. Substrate and ecology: in the Pacific NW common on bark and wood of conifers, especially on twigs; occasional on hardwood trees or shrubs; in open, moderately xeric to mesic forests, in areas with high insolation and occasionally high humidity World distribution: western North America (northern Rocky Mountains and on the east side of the Cascades; British Columbia to Baja California) Sonoran distribution: rare, low elevations in southern California and Baja California. Notes: It is characterized by the bright greenish yellow foliose thallus without soredia and having laminal, immersed pycnidia. Because pulvinic acid derivatives are reported as being restricted to the medulla, the reason why the surface is bright yellow, rather than yellow green as in most species having usnic acid in the cortex, needs to be clarified.