A monograph of Usnea from São Tomé and Principe

A systematic monograph of the lichen genus Usnea from the remote, under-explored islands of Sao Tome and Principe (ST&P) in tropical West Africa is presented, treating 11 species representing 2 subgenera, Usnea and Eumitria. Ten of the 11 species are reported as new for ST&P, including U. firmula, U. baileyi, U. pectinata, U. aff. flammea, U. sanguinea, U. picta, U. krogiana and three undetermined, potentially new species, Usnea species A, B and C. Usnea articulata is confirmed for the main island of Sao Tome. Determinations were made using morphological data, chemistry via thin layer chromatography, and a molecular phylogeny based on nDNA Internal Transcribed Spacer (ITS) sequences. Usnea baileyi, U. pectinata, U. articulata and Usnea species C represent species complexes consisting of two or more morphotypes each. Comprehensive descriptions, photographs, and a dichotomous key to the species are provided.