The genus Otacanthus is revised, integrating results of morphological, chemical, and phytogeographic studies of herbarium specimens and living plants. Seven species and two varieties are recognized. One new species (O. fernandesii) is described and three new combinations (O. platychilus var. platychilus, O. platychilus var. longifolius, and O. azureus) are made. A key to the species is given, as well as descriptions, illustrations, ecology, distribution maps, and a citation of specimens. All species are endemic to southeastern Brazil (coastal region), with one species naturalized in other parts of Brazil, in the Mascarenes, and in the Seychelles.