Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: shrubby-erect to subpendant, 2-15 cm long branching: isotomic- to anisotomic-dichotomous basal part: paler or of the same color as main branches, without conspicuous cracks branches: tapering or irregular; lateral branches: often slightly to distinctly narrowed at attachment points, not or slightly to conspicuously foveate and/or transversally furrowed segments: terete or slightly ridged, cylindrical papillae: absent tubercles: absent fibercles: present, mainly main branches fibrils: 1-2(-3) mm, usually conspicuous, spinulous, easily breaking away, usually densely disposed on some parts of the branches, especially close to the basal part, rarely on whole length of branches, giving spinulous appearance to this part of the thallus soralia: punctiform to slightly elliptic longitudinally (especially on terminal branches), raised, smaller than half the diameter of main branches where they arise mainly on fibercles; typically enlarged on apices where they mainly arise on cortex ab initio, appearing ±fusiform isidiomorphs: occurring on soralia, not blackened at tips cortex: thin (4-8%), glossy, not conspicuously cracked medulla: large, compact to dense, often internally pinkish pigmented axis: moderately thick, often peripherally pinkish pigmented Apothecia: not seen Spot tests: medulla K+ yellow turning red, C-, KC-, P+ orangish yellow Secondary metabolites: cortex with usnic acid; medulla with norstictic (major), galbinic (major) and salazinic (major) acids, or very rarely only with salazinic (major) and norstictic (major) acids or with psoromic acid (major). Substrate and ecology: mainly on bark, rarely on wood or rock, mainly coastal, between 0 and 500 m, on Quercus spp., Pinus spp. in oak-pine forests or on diverse scrubs in the chaparral World distribution: world-wide, North and South America, Africa, Asia and Europe Sonoran distribution: southern California, Baja California, Chihuahua, and Sonora. Notes: This species can be recognized by its lateral branches constricted at ramification points, its numerous spinulous fibrils covering the branches, its minute soralia with isidiomorphs and the presence of galbinic acid in the medulla. Badly developed or old specimens with few fibrils may be difficult to separate from U. cornuta without investigation with t.l.c.