Hibiscus denisonii Burb. came to international attention in English horticulture in 1876, having been sourced from Australian gardens, and generally believed to have come from the South Pacific Islands. It was described as a distinctive creamy white-flowered hibiscus with thick-leathery, dark-green, ‘ivy-like’ leaves that were different from those of other hibiscus then in cultivation. Burbidge’s H. denisonii has a hybrid origin and appears to have almost vanished from cultivation, aside from a morphologically matching hibiscus of undocumented origin growing in the Jardín de Aclimatación de la Orotava, Tenerife, Canary Islands. The name Hibiscus denisonii has long been associated with a similar white to light pink flowered hibiscus species, under cultivation in European botanical gardens, and here described as Hibiscus mabberleyi L.A.J. Thomson. Hibiscus mabberleyi is distinguished from H. × denisonii by its thinner, more slender and hirsute leaves; a more open, upright growth habit and characteristic breeding true-to-type from selfed seed. The genetic affinities of H. mabberleyi are with Mascarene Islands species in sect. Lilibiscus including H. boryanus DC., H. fragilis DC., H. genevei Bojer and and H. liliiflorus Cav. Recommendations are made for further research and ex situ conservation of H. mabberleyi.