Abstract
The systematics of Tryssophyton, herbs endemic to the Pakaraima Mountains of western Guyana, is reviewed and Tryssophyton quadrifolius K.Wurdack & Michelang., sp. nov. from the summit of Kamakusa Mountain is described as the second species in the genus. The new species is distinguished from its closest relative, Tryssophyton merumense, by striking vegetative differences, including number of leaves per stem and leaf architecture. A phylogenetic analysis of sequence data from three plastid loci and Melastomataceae-wide taxon sampling is presented. The two species of Tryssophyton are recovered as monophyletic and associated with mostly Old World tribe Sonerileae. Fruit, seed and leaf morphology are described for the first time, biogeography is discussed and both species are illustrated.