Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: shrubby, subpendant to usually pendant, 5 to 15 cm long branching: anisotomic-dichotomous, usually parallel basal part: concolor with branches to brown or brownish black, with or without inconspicuous annular cracks branches: irregular; lateral branches: not narrowed at point of attachment segments: terete to ridged, cylindrical to slightly swollen or sausage-like; foveoles and transversal furrows: present or absent; apices: long, ± sinuous, often running parallel and densely packed tubercles: nearly absent to numerous, indistinct to verrucose, often eroded and white at top, sometimes confluent and forming striations at the surface of the cortex fibercles: absent and then fibrils numerous or usually and characteristically numerous and dense on main and secondary branches, with a distinct hole in the center fibrils: usually numerous, irregular, and in some parts of the branches dense, polymorphic [short and isidiomorph-like to long and sinuous (2-3 mm)] soralia: absent to numerous, punctiform, smaller than half the diameter of branches, developing on fibercles or on top of tubercles, even to slightly stipitate isidiomorphs: absent to numerous (young fibrils?) pseudocyphellae: absent cortex: thin to thick (5-7%), dull to slightly shiny medulla: loose to dense axis: moderately thick Apothecia: absent to few Spot tests: medulla K+ yellow turning red, C-, KC-, P+ orangish yellow, or K-, KC-, C-, P- Secondary metabolites: usnic acid and salazinic acid (major), or rarely usnic acid alone. Substrate and ecology: on bark (especially Quercus spp. and shrubs) in coastal chaparral or oak-pine woodlands at 200 and 400 m or in the mountains in mixed conifer forests between 2500 and 3000 m World distribution: holarctic Sonoran distribution: southern California, including the Channel Islands (Santa Cruz), and the high mountains of Arizona and Chihuahua. Notes: Usnea scabrata s.l. is a very polymorphic species with numerous transition forms between the different morphs. Characteristic features include its pendulous habitus when optimally developed, numerous fibercles when the fibrils are shed, its irregular branches with ± swollen segments, and its short isidiomorph-like to ±long and sinuous polymorphic fibrils that are often very dense along the branches. Usnea diplotypus has punctiform soralia with clusters of true isidiomorphs; the fibrils are not so numerous and dense fibercles are usually absent. Usnea filipendula has a jet black basal part, branches and segments that are cylindrical and a thicker cortex.