Thallus: shrubby, usually short, up to 5 cm long, rarely longer and subpendant (up to 13 cm), flaccid to stiff; branching: anisotomic-dichotomous, divergent; basal part: concolorous to the branches to pale; branches: main branches irregular, distinctly segmented, ±swollen, lateral branches not narrowed at point of attachment; segments: terete to strongly ridged, cylindrical to ±sausage-like; transversal furrows: numerous, on main branches; papillae: absent (can be mistaken with young fibrils); tubercles: absent; fibercles: nearly absent to numerous, looking like pseudocyphellae; fibrils: young fibrils (0.1-0.5 mm) nearly absent to numerous, covering densely the branches, mature fibrils (1-2 mm) nearly absent to numerous and giving a fish-bone like appearance to the branches; soralia: few to numerous, usually developing on fibercles, punctiform, smaller than half the diameter of the branches; isidiomorphs: absent (can be mistaken for young fibrils); cortex: thin to thick (3-14%), dull to distinctly shiny, never cracked; medulla: lax, dense or compact, not pigmented; axis: thin to wide; Apothecia: rare, small, 1-3 mm in diam., subterminal; Spot tests: medulla K-, C-, KC- P-, or K+ yellow turning slowly orange, C-, KC- P+yellow; Secondary metabolites: either none detected or norstictic acid ±fatty acids (murolic group) or fatty acids alone (murolic group).; Substrate and ecology: on bark and dead trees or wood, very rarely on rock, in the mountains between 650 and 3600 m; World distribution: probably cosmopolitan on every continent; Sonoran distribution: mountains of Arizona, southern California, Baja California and Sinaloa.; Note: Two subspecies of U. hirta are recognized, one widely distributed and one restricted to Baja California. Intermediate specimens occur in the area of overlap.