Hibiscadelphus distans

Hibiscadelphus distans (Hawaiian hau kuahiwi) is one of the world's rarest trees and can only be found on the island of Kauaʻi, Hawaiʻi.

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H. distans is a shrub or small tree up to 18 feet (5.5 m) tall with smooth bark and a rounded crown. The leaves are heart-shaped and covered with star-shaped hairs. The flower is about 1 inch (3.5 cm) long and barely opens.

It is found within low to mid-elevations, between 1,000 to 1,800 feet in highly degraded remnants of native dryland forests. The substrate is basaltic bedrock overlain by dry, crumbly red-brown soil.

There are only two known naturally occurring populations with an estimated total of 80 to 200 trees. The original population, found in 1972, was located within the State-owned Nā Pali Kona Forest Reserve, Koaiʻe Canyon. In 1989, this population was destroyed by a landslide. Three botanical gardens in Hawaiʻi have cultivated this plant species: National Tropical Botanical Garden on Kauaʻi, and Waimea Valley Audubon Center and Lyon Arboretum on Oʻahu.

The original habitat of H. distans is a remnant of a native, open, dryland forest. The mean temperature ranges from 18.5 to 25.7 °C (65 to 78 °F).[1]

Despite the extreme rarity of H. distans, it actually has the largest wild population of any Hibiscadelphus species. Five of the other six species are extinct or extinct in the wild (four were only ever known from a single wild tree), the exception being H. woodii (also from Kauaʻi), which is known from only four individuals.