Abstract

Summary Rhododendron boninense Nakai, illustrated here, is a critically endangered endemic rhododendron from the Ogasawara Islands, whose population was once reduced to a single individual. Since the 1980s, Koishikawa Botanical Garden has made efforts to propagate and reintroduce this species to its original habitat, resulting in a current population of 60 mature plants and several natural seedlings. The pure white corolla, which lacks a nectar guide, is distinctive among related rhododendrons, suggesting that a pollinator shift occurred after colonisation of the Ogasawara Islands, where the ancestral pollinators are absent.