Ten new combinations from Asagraea, Isidrogaliva, and Tofieldia are proposed in the previously monospecific genus Harperocallis (Tofieldiaceae, Alismatales). As circumscribed here, the genus is restricted to the Americas. The majority of species occur in the Andes or the Guayana region of northern South America; more than half have restricted distributions, and Harperocallis flava is narrowly endemic in the Coastal Plain of the southeastern United States. A key to species, synonymies, distributions, representative specimens, and salient notes are presented. Populations of the species are mapped and Harperocallis robustior is illustrated. A neotype is selected for Tofieldia frigida, here considered a synonym of Harperocallis falcata. Several recent records of Harperocallis longiflora, previously known only from the type collected in 1902, are reported.