Recent botanical explorations in western tropical South America provide new documentation of Joosia H. Karst., which has clarified some species identities and discovered some new species. Eighteen species are recognized here, with J. umbellifera H. Karst. circumscribed more narrowly than in previous taxonomies and J. panamensis Dwyer and J. ulei Steyerm. separated from it. Two new nomenclatural combinations are made: J. loretensis (Standl.) C. M. Taylor is based on Rondeletia loretensis Standl., and J. sericea (Standl.) C. M. Taylor is based on Ladenbergia sericea Standl. and is an older name for J. multiflora L. Andersson. Three species are newly described here: J. capitata C. M. Taylor from northern Peru, with subcapitate inflorescences and dense hirtellous to hirsute pubescence; J. confusa C. M. Taylor from Ecuador and Peru, with dichasial axes and shallowly lobed calyx limbs; and J. frondosa C. M. Taylor from Colombia, with enlarged whitened bracts and calyx lobes. Joosia has its center of species diversity in montane Ecuador and Peru; it is now documented also from Bolivia, where J. sericea is found, and from Venezuela, but that material is inadequate for identification to species.