Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: erect-shrubby, subpendulous to pendulous, up to 50 cm long, coarse and ±stiff branching: isotomic- to anisotomic-dichotomous, divergent to parallel basal part: concolorous with or paler than the branches, sometimes with a pale yellow to dark brown pigment branches: cylindrical to irregular; lateral branches: not narrowed at point of attachment, not or slightly to conspicuously foveate and/or transversally furrowed segments: conspicuous, terete to strongly ridged, cylindrical to slightly sausage-like or trapezoidal papillae: nearly absent to frequent especially on main branches, low and indistinct to verrucous tubercles: sparse to numerous, especially on smaller branches, conspicuously raised, sometimes eroded at summit, never bursting into ulcerose soralia fibercles: irregularly present fibrils: nearly absent to numerous, spinulous 1-3(-10) mm) long, irregularly distributed soralia: absent isidiomorphs: absent pseudocyphellae: at top of eroded tubercles cortex: thick (8-16%), shiny to vitreous, hard, smooth to very cracked medulla: thick, dense to compact, rarely loose, wine red, pink and/or yellow pigmented, rarely not pigmented axis: thick, white to pink or yellow pigmented, or not pigmented Apothecia: terminal, subterminal or lateral, 1.5 to 5 mm in diam. Spot tests: K+ yellowish, C+ yellow, KC+ yellow, P- Secondary metabolites: diffractaic acid (major), ±barbatic acid (minor), ±4-O-demethylbarbatic acid (minor), ± several accessory substances and fatty acids. Substrate and ecology: on bark World distribution: Mexico Sonoran distribution: Sierra Madre of Chihuahua and Sinaloa. Notes: With its pigmented medulla reacting C+ yellow and its numerous apothecia, U. cristatula is a very characteristic species. It is closely related to U. ceratina, from which it differs essentially by its strategy of reproduction.