Herbarium studies leading to a treatment of the Myrsinaceae for the Flora of Central French Guiana resulted in the discovery of two heretofore undescribed species, Cybianthus prevostiae and Stylogyne incognita. The species are described and illustrated, and hypotheses regarding phylogenetic relationships with their respective congeners are provided. Cybianthus prevostiae is unusual among members of Cybianthus subgen. Weigeltia owing to its monoaxial habit and ellipsoid pistil, and deeply cupuliform calyx. Stylogyne incognita, a taxon often confused with S. micrantha, is most closely related to S. sordida but is separated from it by the corymbose inflorescence, entire leaves, longer petioles, and membranaceous perianth.