Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Segments: ±cylindrical to moderately sausage-like cortex: thin to moderately thick (5-9%) medulla: moderately thick (25-36%), lax to dense central axis: thin to moderately thick (17-30%) Spot tests: K+ yellow turning red, C-, KC-, P + orangish yellow, or K+ dull yellow turning reddish orange, C-, KC-, P+ deep yellow, or K+ yellow slowly turning pale orange, C-, KC-, P+ deep orange of K-, C-, KC-, P- Secondary metabolites: salazinic acid (major), ±consalazinic acid (minor), ±protocetraric acid (minor), ±norstictic acid (minor), ±lobaric acid (minor), ±fatty acids (minor); norstictic acid (major), ±fatty acids (minor) or norstictic acid (major), lobaric acid (major), or stictic acid (major), norstictic acid (major), ±constictic acid (minor), ±cryptostictic acid (minor), ±menegazziaic acid (minor); or none detected . Substrate and ecology: on bark, rarely on wood, in mixed oak-conifer or spruce-fir forests at high elevations or in coastal areas with chaparral or exposed low oak forests, more rarely on rock in the chaparral World distribution: Europe, Macaronesia, eastern and western North America, South America, Japan, and Australia Sonoran distribution: mountains of SE Arizona, southern California, Cedros Island in Baja California, and the Sierra Madre Occidental of Sinaloa. Notes: Typical for U. cornuta are the lateral branches distinctly narrowed at the ramification points, the glossy cortex and the minute soralia with isidiomorphs on the terminal branches. In western North America U. cornuta and U. fragilescens are harder to distinguish than in Europe and eastern North America because of the presence of intermediate forms and a larger range of morphological variation. In some populations of western America these two species are indeed very difficult to distinguish. There are morpho-types that are intermediate between the two species, e.g. a specimen collected on Cedros Island with a typical U. cornuta thallus morphology but with soralia of the U. fragilescens type and norstictic acid in the medulla. Secondary metabolite: protocetraric acid (major).