Recent linguistic, morphological, and DNA studies have shown that the Polynesian hibiscus known as kaute—koute, ‘aute, and other cognates—is an undescribed eastern Polynesian Hibiscus species in sect. Lilibiscus. It is described here as Hibiscus kaute L.A.J. Thomson & Butaud, and appears to be extremely rare, if not extinct in the wild. The French botanist Jean Nadeaud (1873) recorded ‘aute in a wild state during the 1850s at the end of Pirae valley (Nahoata) and elsewhere in the interior of Tahiti where it grew on cliff faces. The original wild form—with a single whorl of petals—is also rare in cultivation, both in French Polynesia and elsewhere in the South Pacific Islands. The medicinal Polynesian double-flowered form is uncommon in cultivation and often mistaken for recently-introduced cultivars. As well as being of great cultural importance to Polynesians, kaute is arguably the most significant species in the development of modern Hibiscus hybrids and a missing link in understanding the origins of H. rosa-sinensis. Ex situ conservation measures are urgently needed in French Polynesia (Tahiti and Marquesas Islands) and, internationally, in botanic gardens, for this important progenitor species of Lilibiscus hybrids.