Abstract
This treatise serves as a preliminary monograph and phylogenetic treatment of Marasmius from the African island nation of São Tomé and Príncipe (ST&P), based on data generated from 30 specimens collected in 2008. Twenty-one species are described, seven of which represent species new to science (Marasmius albisubiculosus, M. diversus, M. elaeocephaliformis, M. laranja, M. leptocephalus, M. paratrichotus, M. segregatus), and all represent new distribution records for ST&P. Species are delimited based on comprehensive morphological characters and DNA sequence data. Prior to the collection of these specimens, only one Marasmius species had been documented from these islands. Phylogenetic hypotheses generated from analyses of DNA sequences of the Internal Transcribed Spacer regions (ITS1+5.8S+ITS2) are proposed to explore the evolutionary relationships amongst ST&P Marasmius and global Marasmius diversity. A dichotomous key to aid in identification, illustrations of pertinent micromorphological features, colour photographs of basidiomata, comprehensive descriptions and commentaries are provided.