Abstract
Limited research has been published on the mushroom-forming basidiomycetous fungi of the oceanic islands São Tomé and Príncipe, West Africa. Based on field work in April 2006 and 2008, which generated 24 specimens of mycenoid fungi, we recognize 14 species of Mycena, and 5 species belonging to the allied genera Clitocybula, Filoboletus, Hydropus and “Trogia”. Of these, 9 species are recognized herein as new to science, viz., Mycena antennae, M. brunneoviolacea, M. longinqua, M. oboensis, M. phaeonox, M. solis, Clitocybula intervenosa, Hydropus globosporus, and H. murinus; an additional 10 species are new distribution reports for São Tomé and Príncipe. Species delimitations are based on comprehensive morphological descriptions and molecular sequence (nLSU, ITS) data. Line drawings of salient micromorphological features, colour photographs of basidiomata, comparisons with allied taxa, a key to aid in identification, and phylogenetic inferences are provided.