Bungartz F., Truong C., Herrera-Campos M. & Clerc P. 2018: The genus Usnea (Parmeliaceae, Lecanoromycetes) in the Galapagos Islands. – Herzogia 31: 571–629.
As part of an ongoing, comprehensive inventory of all Galapagos lichens, the genus Usnea is revised. In Galapagos this genus is represented by 27 species. Although 23 species had previously been reported, two are synonyms, and seven historic records must now be considered erroneous. Nine species are reported here for the first time and an additional four are described new to science: Usnea mayrhoferi, U. leana, U. patriciana, and U. subcomplecta. With two species previously described as new, U. clerciana and U. galapagona, six of the species now known are presumed to be endemic (22 %), a proportion of endemism similar to percentages reported for other, recently reviewed groups of Galapagos lichens. For two species, U. angulata and U. subflammea, only historic collections are currently known. Usnea angulata, with its trapezoid branch segments, is a very conspicuous, easily identified species. Despite thoroughly revisiting its historic collection sites, no material was found again and this species is therefore presumed to be locally extinct. Usnea subflammea, however, is less easily recognized and its original collection sites have not been intensively surveyed again. It is thus possible that this species is rare and overlooked, but not necessarily extinct. Characteristics of all species are illustrated and an identification key emphasizes their diagnostic characters. Detailed descriptions are provided for all newly described species and for those previously not well-documented.