Diagnosis. Thallus pendulous, entangled with several inconspicuous hapters, branches irregular and slightly inflated, covered by punctiform pseudocyphellae, soralia plane, enlarging at maturity, cortex glossy, medulla dense, axis moderately thick, with galbinic acid.
Type: Ecuador. Galápagos, Isla Floreana, trail going to Post Office Bay off the dirt road between highlands and Puerto Velasco Ibarra, 1°17.0'58.7''S, 90°26.0'51.1''W, 342 m alt., transition zone, agricultural area; farmland (bananas, orange and guajava trees) with fences, on twigs of Croton scouleri, 14-Jan-2011, Yánez-Ayabaca 1895 [holotype in CDS (48250)]. %C/M/A: 10.5/19.5/39.5. Chemistry: Usnic, galbinic, norstictic and salazinic acid.
Etymology. Named after Lea Bungartz, the daughter of the first author of this publication.
Description.Thallus entangled, with several inconspicuous hapters and branches enrolling around the substrate; ramifications ±anisotomic-dichotomous; trunk with several hapters, often inconspicuous, concolorous with basal branches or slightly brownish; branches of irregular diameter, slightly inflated on basal branches; lateral branches not constricted at ramification; maculae absent; pseudocyphellae minute, most conspicuous on basal branches; papillae, tubercles, fibrils and fibercles absent; soralia developing from pseudocyphellae on terminal branches, remaining plane, enlarging to the branch diameter at maturity, almost excavate, with a circular to ±irregular outline; isidiomorphs sparse, short; cortex glossy in section, moderately thick, 9 –10.5 %; medulla ±compact to dense (hyphae visible individually), 19.5 –22.5 %; axis white to slightly pinkish, 36.5 –39.5 %, with an A/M-ratio > 1.5; apothecia and pycnidia not observed.
Chemistry. Medulla with galbinic, norstictic, and ±salazinic acid [P+ orange yellow, K+ yellow turning orange-red (crystals) or K+ yellow turning deep red, C–, KC–].
Ecology and distribution. So far endemic to the Galapagos; the species is currently known only from two localities representing the collection sites of the holotype and paratype.
Notes.Usnea leana can be readily recognized by a thallus closely entangled around its substrate, attached by several hapters. It is the only species in the Galapagos attached by multiple holdfasts. Its thallus surface is dotted by minute pseudocyphellae and punctiform soralia, which enlarge at the terminal branches. In the Galapagos U. deformis is the species most similar to U. leana (for differences see comments there). In the tropical Andes, Usnea amabilis has a similar morphology, also with an entangled thallus and branches dotted with pseudocyphellae. While U. amabilis has a pruinose, opaque cortex (i.e., mat in section), the cortex of U. leana is glossy in section. Usnea amabilis has soralia that are not significantly larger at the terminal branches and it also has a different chemistry (constictic acid).