Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: shrubby to subpendulous, 2 to 10 cm long branching: strongly anisotomic-dichotomous basal part: brownish black to distinctly jet black branches: irregular, lateral branches not narrowed at point of attachment segments: terete to slightly flattened or distinctly striated, ±cylindrical, sometimes slightly swollen tubercles: usually numerous especially on main branches, low and verrucous fibercles: few to numerous fibrils: numerous especially on main branches, varying in lengths, irregularly arranged and sinuose soralia: punctiform, smaller than half the diameter of the branch, plane to convex, sometimes slightly stipitate and efflorescent, not confluent, arising mainly on top of the tubercles isidiomorphs: generally numerous, in clusters on young and mature soralia cortex: distinctly shiny, moderately thick (7-9%) medulla: moderately thick, lax to dense axis: moderately thick Apothecia: not seen Spot tests: K+ dull yellow turning reddish orange, C-, KC-, P+ deep yellow, or K+ yellowish, KC+ yellow, C+ yellow, P- or K-, P-, C-, KC- Secondary metabolites: norstictic acid or diffractaic acid or none detected. Substrate and ecology: on bark or wood of Pinus muricata, Pachycormus spp. and Juniperus spp. in north facing slopes of ridges crests between 300 and 400 m World and Sonoran distribution: Cedros Island, Baja California. Notes: Usnea cedrosiana is characterized by the punctiform soralia born on top of the numerous tubercles, the irregular branches that are usually ±striated, the lateral branches that are not narrowed at point of attachment, the blackish basal part, the shiny cortex, the numerous fibrils of varying lengths irregularly disposed on main branches and the chemistry. Usnea hirta has no tubercles, a pale basal part and numerous foveoles or transversal furrows. Usnea diplotypus has soralia arising initially on the cortex, a dull cortex and a different chemistry. Usnea scabrata has soralia arising on fibercles without isidiomorphs, a dull cortex and a different chemistry.