Galapagos Species Database

Thallus erect-shrubby to subpendulous, to 12 cm long, often fragile and easily breaking; ramifications anisotomic dichotomous, with few ramifications; trunk concolorous with the branches; branches strongly irregular; segments strongly deformed to almost ridged, especially close to the base, not inflated; lateral branches not or slightly constricted at the attachment point; foveoles often present, especially on main branches close to the base; maculae absent; papillae numerous, indistinct to hemispherical, developing into minute, slightly stipitate soralia; fibrils absent, not to be confused with the numerous delicate isidiofibrils growing from minute soralia (never as rigid as true fibrils); soralia numerous, remaining minute, developing on the cortex of branches, often along the ridges, giving the branches a slightly angular aspect; isidomorphs numerous (sometimes eroded in old herbarium specimens), often completely covering the branch surface and hiding the soralia, giving the impression that they are growing directly on the cortex, leaving minute scars on the branches when eroded, turning into isidiofibrils when growing in size; cortex 4.5–6.5%, thin and fragile, shiny in section; medulla 30.5–35.5%, dense, with an orange, 6 continuous pigmentation just below the cortex; axis 18.5–28.5%, moderately thin, often distinctly pinkish, with an A/M ratio usually , 1.25 (n 5 22); apothecia and pycnidia not seen. Chemistry. Medulla K+ yellow turning red, P+ yellow to orange: salazinic, galbinic, norstictic, lobaric acids (n = 22).

Usnea poliotrix is characterized by the very irregular branches, often ridged and bearing foveoles, the absence of fibrils with instead numerous isidiofibrils covering the branches, and the orange subcortical medulla pigmentation. The combination of these characters in addition to the minute soralia, the very thin, easily breaking cortex and the presence of lobaric acid in the medulla readily distinguish this species from any other Usnea. The type specimen lacks isidiofibrils (apparently all eroded), but has the characteristic irregular and slightly ridged branches, with minute scars on the branch surface.