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DescriptionThallus: erect-shrubby to subpendulous, 1.5 to 9 cm long, stiff; branching: ±isotomic-dichotomous especially towards the tips, divergent to subparallel; basal part: concolorous to reddish brown, pigmented at the very base, rarely black; branches: cylindrical to tapered, lateral branches not narrowed at attachment point, foveoles or transversal furrows absent; segments: terete and cylindrical; papillae: few to numerous, irregularly distributed on secondary branches; tubercles: absent; fibrils: nearly absent to few, rarely numerous, slender (2-3 mm long) scattered on the branches, especially close to basal part; soralia: numerous on secondary and terminal branches, punctiform, minute, smaller than half the diameter of the branch, fusing together and looking thus like a single large soralium, circular or of irregular shape, without a sharply delimited cortical rim, even, developing initially on the cortex; isidiomorphs: numerous on mature soralia but sometimes covering densely all the branches; pseudocyphellae: absent; cortex: thin to moderately thick (6-9%), dull to slightly shiny, without distinct cracks, often parasitized by lichenicolous fungi and then with pale brown or pale red pigmented zones (sometimes with small aggregated red dots at summits of papillae); medulla: extremely thin (5-14%), dense to compact, unpigmented; central axis: extremely large (50-80%); Apothecia: not seen; 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-, C-, KC-, P-; Secondary metabolites: either salazinic acid or norstictic acid and fatty acids or none detected.; Substrate and ecology: on bark on Quercus spp. (but especially Q. pacifica) and Arctostaphylos spp. in oak stands or scrubs between 200 and 500 m; World and Sonoran distribution: Channel Islands of southern California and Isla Cedros in Baja California.; Notes: The thick axis and thin medulla giving the stiffness to the thallus, the absence of tubercles, the numerous punctiform soralia with isidiomorphs make Usnea brattiae very distinct. Among other species with such a thick central axis, U. schadenbergiana differs by the pendulous habitus, the numerous and long fibrils arranged in ±fish-bone like pattern, the sparse isidiomorphs and the chemistry; Usnea transitoria differs by the pendulous habitus and ridged to distinctly alate branch segments; Usnea baileyi differs by the pink pigmented medulla, the fistulose axis and the chemistry.