Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: pendulous, up to 60 cm long, flaccid hanging loosely on branches and twigs branching: isotomic-dichotomous, distinctly parallel basal part: paler than or concolorous with the branches, sometimes with several attachment points branches: cylindrical to irregular, tapering very slowly, commonly conspicuously foveolate segments: not conspicuous, terete, striate, or weakly ridged, cylindrical papillae, tubercles and fibercles: absent fibrils: absent to scarce and irregularly distributed, 1-3 (5) mm long isidiomorphs: absent pseudocyphellae: thin fusiform to elongate-sinuous cortex: thin (3-5%), shiny and smooth, with thin transverse cracks medulla: dense, not pigmented axis: typically sinuous Apothecia: very rare Spot tests: K-, C-, KC-, P- or K+ yellow turning red, C-, KC-, P+ orangish yellow Secondary metabolites: either no medullary substances or salazinic acid. Substrate and ecology: on bark, rarely on wood, in mountains in moist habitats between 2000 and 3300 m World distribution: Eurasia and North America Sonoran distribution: Arizona, Baja California, Chihuahua, Sinaloa and Sonora. Notes: Usnea cavernosa is easily distinguished by its pendant and flaccid habit, the slender, smooth and foveolate branches with numerous thin elongate-sinuous pseudocyphellae not developing into soralia and lacking papillae.