Overview
Kilauea Hau Kuahiwi (Hibiscadelphus giffardianus), known in Hawaiian as hau kuahiwi (mountain hau), is one of the rarest flowering trees on Earth, belonging to the mallow family (Malvaceae). Endemic strictly to the volcanic slopes of Kilauea on Hawaii Island, this exceptional species was discovered in 1911 by botanist Joseph Rock as a single surviving wild tree in Kipuka Puaulu (Bird Park). While the original wild tree died in 1930, forward-thinking horticulturalists successfully propagated cuttings and seeds, saving the species from total biological extinction through dedicated botanical guardianship.
Biology and Physical Characteristics
Hibiscadelphus giffardianus develops into a graceful small tree with a spreading, rounded canopy and smooth grayish-brown bark. Its foliage consists of broad, cordate (heart-shaped) alternate leaves with undulating margins, adorned with stellate hairs on their undersides. Its flowers are marvels of co-evolutionary specialization: rather than opening widely like conventional hibiscus blossoms, the petals remain tightly overlapping to form a curved, tubular, zygomorphic trumpet colored rich yellowish-green suffused with intense magenta and wine-red. A long, slender staminal column projects gracefully beyond the petal tips.
Behavior and Ecology
The specialized curved tubular architecture of Hibiscadelphus giffardianus flowers evolved in strict mutualistic tandem with native Hawaiian honeycreepers (Drepanidinae), particularly species with long, decurved bills such as the extinct Hawaii mamo (Drepanis pacifica) and the endangered iiwi (Drepanis coccinea). In exchange for copiously secreted, dilute nectar pooled at the flower’s base, foraging birds brushed their forehead plumage against the exerted anthers, cross-pollinating isolated trees across kipuka forest islands.
Conservation and Human Impact
The primary causes behind the historic wild extinction of Hibiscadelphus giffardianus include heavy browsing by introduced feral cattle, goats, and pigs, as well as seed predation by black rats and the dramatic decline of its specialized honeycreeper pollinators. Modern conservation biologists within Hawaii Volcanoes National Park have established fenced, ungulate-free reintroduction enclosures in Kipuka Puaulu, where dozens of clonally propagated individuals now thrive under active ecological stewardship.
Interesting Factoid
Every single Kilauea Hau Kuahiwi tree alive on Earth today descends from a solitary wild tree found growing on the rim of Kilauea volcano over a century ago, and its curved red flowers were custom-shaped by evolution to fit the curved beaks of native Hawaiian honeycreepers!
Last updated: October 2026