Hibiscadelphus distans flower and leaves. Hau kuahiwi has five-chambered fruit capsules that split open when ripe to reveal their fuzzy seeds. A cultivated hau kuahiwi; this plant is several years old.

Growth Requirements

General

    Hibiscadelphus distans is a unique plant rarely seen in Hawaiian landscapes, which is unfortunate since it does well at lower elevations. As an in-the-ground accent or container plant, it has a fascinating story concerning its history of scientific discovery, evolution, and relationship with Hawai‘i's native birds.

     Hau kuahiwi does best in a site with full sunlight for all or most of the day, but can also survive in a (very) bright shaded space. Once established in the ground (3 to 6 months), keep watering to a minimum. Hau kuahiwi does better with occasional heavy drenches during the hot dry months rather than frequent light waterings. Too much water will yield large flaccid leaves and little to no flowers. Even worse, overwatering will favor fungal root rot problems, as well as black sooty mold on the leaves, and is a good way to kill your hau kuahiwi. Hau kuahiwi is tolerant of extreme heat and drought, and will grow in lava/cinder, organic-, and clay-dominant soils, provided there is good drainage; container plants should have an easy-draining media mix. If your site has poor drainage, improve it by mounding up the soil and planting your hau kuahiwi on top of the mound.

    While Hibiscadelphus distans is recorded to grow into a small tree, we have never grown or seen a hau kuahiwi taller than six feet. Perhaps, it takes a really long time to obtain treelike stature; my ten-year-plus H. distans are still about four feet (1.2 m) tall. Initially, hau kuahiwi grows quite quickly when placed in the ground, becoming 2 to 3 feet tall within two years. This is also when they begin flowering and fruiting. 

    In the ground, hau kuahiwi doesn't seem to need any fertilizer. However, an occasional (no more than once a month) foliar feeding with a diluted fertilizer at half recommended strength or less may improve growth and flowering; use a fertilizer with a low nitrogen value. Overfertilizing, like overwatering, will produce large flaccid leaves, fewer flowers, and attract insect pests. Hand-prune your shrub only if necessary, and do not remove too much woody material at any one time. 

Pests and Diseases

    The leaves of hau kuahiwi are often eaten by Chinese rose beetles, or occasionally infested by whiteflies. Protected by ants, aphids, mealybugs, and thrips can also become a problem; they normally attack the stem-tips or flowers. Others have reported their hau kuahiwi being attacked by black twig borers. Refer to the Pests & Diseases page for ways to deal with each of these pests. 

Special Features and Information

General

    The large Mallow family, Malvaceae, contains about 4,200 species, with notables such as okra, cacao, durian, baobab, kenaf, and cotton [WikipediA;Malvaceae]. Hibiscadelphus is an endemic Hawaiian genus of eight endangered or extinct species. It is a complex genus and is considered to be one of the rarest groups of plants in the world. Here is a species summary based on [Baker 1980] and [WikipediA;Hibiscadelphus]:

• Hibiscadelphus bombycinus — Presumed extinct. Known from a single collection before 1868 from Kawaihae, Hawaiʻi.

• Hibiscadelphus crucibracteatus — Presumed extinct. A single tree was discovered in 1981 on the slopes of Puhielelu Ridge on Lānaʻi (altitude 2,460 ft). This tree died in 1985, and all efforts to save the species failed because none of the collected seeds germinated.

• Hibiscadelphus distans — As of 2020, about 25 wild plants exist above the Koaiʻe River on Kauaʻi. However, fertile seeds have been collected, and the species is in limited cultivation.

• Hibiscadelphus giffardianus — Joseph Rock discovered a single tree in 1911 at Kīpuka Puaulu, today part of Hawaiʻi Volcanoes National Park. This plant died in 1930, but cuttings were collected and rooted. Since then, several hundred clones have been planted in the park, but no natural regeneration has been observed, and only a few trees produce viable seeds.

• Hibiscadelphus hualalaiensis — The last wild tree (growing in North Kona, Hawaiʻi) died in 1992, but the species survives in cultivation, and trees have been outplanted in forest reserves.

• Hibiscadelphus stellatus — A recently discovered and described species with about 100 wild plants in Kaua`ula Valley in Western Maui. This species is also in cultivation at State nurseries.

• Hibiscadelphus wilderianus — Presumed extinct around 1912. Known from a single tree discovered at Auwahi on Maui.

• Hibiscadelphus woodii — Discovered in 1991 on Kauaʻi. Only four plants were found at that time. Unfortunately, three were crushed by a boulder and died between 1995 and 1998, and the last was seen dead in 2011. Collected pollen was found to be inviable, no fruit was ever observed, and all attempts at propagation, including cross-pollination with H. distans, have failed. However, one plant was discovered on a cliff in Kalalau Valley in 2019, and a month later, two more were found.

• Hibiscadelphus x puakuahiwi — An unnatural hybrid between H. giffardianus and H. hualalaiensis. In the 1960s, both species were planted in Hawaiʻi Volcanoes National Park, where only the former occurred naturally. The two species cross-pollinated and hybrid seeds were unknowingly collected and planted. Since these two species do not naturally exist together and threatened the genetic integrity of H. giffardianus, the hybrids and the planted H. hualalaiensis were destroyed after their discovery in 1973, although at least one hybrid remains as of 2011. Other hybrids likely exist elsewhere in cultivation.

Saving a Rare Hibiscadelphus From Extinction

    A 2002 National Parks article entitled A Tree's Tribulation by Jenell Talley relates how a plant teetering on survival can be saved from total extinction by the efforts of a few conscientious people.

   "Hibiscadelphus giffardianus, also called hau kuahiwi, is endemic to Hawaii Volcanoes National Park. The species was first described in 1911 by Austrian botanist Joseph Rock. Before the original tree died in 1930, cuttings were collected and at least one tree was propagated on land adjacent to what is now Hawaii Volcanoes. This tree died in 1940, but one cutting remained, keeping the species alive. The plant survived in cultivation and was replanted in the park in the 1950s. The species has been reduced to a single tree at least three times. Each tree is derived from the 1911 original."

She continues: "Steps are being taken to increase the tree population, although currently Belfield, Linda Pratt, a botanist working for the U.S. Geological Survey Pacific Islands Ecosystems Research Center, and Tim Tunison, chief of resources management at Hawaii Volcanoes, are the only scientists dedicated to the recovery effort. The tree has no specific recovery program, but Belfield is working on the park's Rare Plants Stabilization Project, which began last year. The project focuses on examining the status of rare and endangered plant species, including the H. giffardianus, in four ecological zones in the park. Seeds, fruit, and cuttings are collected and raised in the park's greenhouse, then planted in the park. More than 200 trees have been planted in the last few years as part of an experiment conducted by U.S. Geological Survey researchers to study damage caused by rats. Despite these efforts, more work remains before the trees can make it off the endangered list. 'It is unrealistic to imagine that this species will ever be delisted unless it goes extinct,' Pratt says, adding, that reintroducing the species to its natural habitat and having it be self-sustaining is the park's goal."

Hawaiian Name

    Hau kuahiwi translates to "hau of the mountains," referring to its mountain (kuahiwi) habitat and how its leaves resemble those of hau (Hibiscus tiliaceus), a Polynesian-introduced plant most frequently found in the lowlands [Pukui & Elbert 1986].

Etymology

    Hibiscadelphus is from the Greek words hibiscum, meaning "marsh mallow," and delphi, meaning "brother" [Gledhill 2008]. Together, they translate as "the brother of the marsh mallow," suggesting their close affiliation to the genus Hibiscus. The species name, distans, comes from the Latin disto or distare, meaning "distant," a reference to the geologically distant range of this species from Hibiscadelphus spp. on the other islands of Maui and Hawaiʻi Island, as well as the observation that the fruit morphology stands apart from the others in the genus [Baker 1980].