Usnea deformisMotyka Lich. Gen. Usnea Monogr.2: 485, 488 (1937).
Short Description. This species is readily distinguished by its fragile thallus with a thin cortex and axis, deformed and often foveolate branches, which are constricted at their ramification and soralia bearing isidiomorphs abundantly covering the branches (for a detailed description see Truong et al. 2013b, Herrera-Campos 2016). Branches of U. deformis are typically divided into thick, inflated segments, frequently (but not always) showing annular branch regeneration, where branches were torn apart, exposing the axis. The newly described U. leana is superficially similar, but it lacks this distinct annular branch regeneration. Overall branches of Usnea deformis appear much more strongly deformed and typically have abundant foveoles. Branches of U. leana are by comparison more regularly terete and spotted by punctiform pseudocyphellae. The two species also differ in their CMA: Usnea deformis has a very thin cortex (<5 %) while the cortex of U. leana is moderately thin (ca. 10 %). Finally, specimens of U. deformis lack the multiple holdfasts characteristic of U. leana. For differences with U. articulata and U. dimorpha, see Truong et al. (2013b).
Chemistry. Medulla with norstictic and connorstictic acid, and unidentified triterpenoids [P+ yellow, K+ yellow turning orange-red (crystals), C–, KC–].
Ecology and distribution. When Truong et al. (2013b) reported this pendulous species from continental South America (Bolivia, Colombia, Peru, Venezuela), the species was previously known only from North America (California, Mexico). The single specimen reported here from the Galapagos is a new record for the archipelago. It was discovered on branches of Psidium galapageium, an endemic tree.