Short Description. A detailed description is available in Clerc (2006). The distinctly pendulous U. geissleriana is characterized by irregular branches not constricted at their ramification and divided by thin annulations into terete to slightly swollen segments. These annulations are most distinct along the basal branches and the trunk. The branches of U. geissleriana are not constricted at their ramification and have a slightly to strongly pruinose surface, which is sometimes spotted with faint maculae and/or minute pseudocyphellae. Fibrils are mostly absent, rarely sparse. The soralia of U. geissleriana are minute, barely enlarging, plane to slightly stipitate, at maturity sometimes capitate, aggregating in ±irregular clusters on lateral/terminal branches, with short isidiomorphs. The species has a dense medulla, with an A/M-ratio < 1.5. It might be sometimes difficult to distinguish this species from U. subflammea, which becomes pendulous at maturity, but, like the erect U. flammea, has thalli that are abundantly covered by fibrils and can further be distinguished by the strongly tuberculate branches with apically eroded tubercles.
Chemistry. Medulla with stictic, constictic, and rarely ±norstictic acid [P+ deep orange, K+ yellow slowly turning orange (±crystals), C–, KC–].
Ecology and distribution. Usnea geissleriana is an oceanic species, originally described from Macaronesia (Clerc 2006); subsequently it was reported by Clerc (2011b) from the southern Atlantic (Tristan da Cunha) and Truong et al. (2013b) later discovered it in continental South America (Bolivia, Brazil, Ecuador, Peru, Venezuela); in Galapagos U. geissleriana appears to be rare, this new report is based on only two records.