Rauvolfia sandwicensis
Apocynaceae or Dogbane family
Synonyms: Excavatia sandwicensis, Ochrosia sandwicensis, Rauvolfia degeneri, Rauvolfia forbesii, Rauvolfia helleri, Rauvolfia mauiensis, Rauvolfia molokaiensis, Rauvolfia molokaiensis var. parvifolia, Rauvolfia remotiflora, Rauvolfia sandwicensis var. subacuminata
Hao
Natural Range & Environment
Rauvolfia sandwicensis is endemic to all the main Hawaiian Islands except Kaho‘olawe. Wagner et al. [1990] state that hao is found primarily in mesic forests and even wet forests. However, this has not been our experience on O‘ahu and Maui. Rather, our observations suggest hao’s primary habitat is dry forests and, occasionally, the gulches of dry shrublands. Hao can also be seen growing on old lava flows on Maui and Hawaiʻi Island.
A party-favors net bag around unripened hao fruits works well to deter birds and rats, which love to eat the ripe fruits and seeds, respectively. The shiny leaves of hao tend to cluster at the branch tips. This five-year-old semi-cultivated hao is about a year away from its first flowering. Hao can be bushy, like this mature wild "tree" in a dry lava field on Maui, while others assume a more typical tree shape, such as these young hao ready for sale at a Maui nursery (Shiny leaves, bushy mature hao, and hao for sale photographs all courtesy of Forest & Kim Starr CC BY 2.0).
Description
Rauvolfia sandwicensis is an increasingly uncommon long-lived (greater than five years) tall shrub to medium-sized tree (to about 30 feet [9 m]). It has nearly white bark, which acquires a bumpy texture as it gets older, and a milky sap. The glossy light-green leaves have a prominent midrib and tend to cluster/whorl at the branch tips. Hao's tiny greenish-white perfect (bisexual) flowers are also clustered and have a fragrance similar to plumeria — not surprising since both species belong to the same family, Apocynaceae. The flowering and fruiting of hao is a variable event with different populations fruiting at different times of the year and even a single hao’s flowering being influenced by the rainfall that year. In cultivation, hao can flower and set fruit more than once each year. Hao fruits are about the size of a grape, dark purple or black when ripe, and often bilobed, with each lobe containing one tan laterally-compressed wrinkled seed.
Growth Requirements
General
Rauvolfia sandwicensis is a beautiful accent tree in a landscape. More functionally, it can also be an excellent shade tree with a little pruning, or strategically planted to hide your neighbor's unsightly whatever.
Hao does best when planted in a site with full sunlight for all or most of the day and will become spindly if planted in a constantly shaded site. Water your hao once a week for a few months until its roots are fully established, and then about once a month (or less) to prevent any drought stress (e.g., wilted or dropped leaves).
Hao doesn't seem to be too fussy about the type (lava/cinder, clay, organic-dominant) soil it is planted in, provided it drains well. Established plants can tolerate extreme heat, moderate drought (with some leaf loss), and strong winds.
After five years, maybe sooner with watering and fertilizer, your hao should be about ten feet (3 m) tall and flowering. Hao is best left as a free-forming tree, and when planted in the open, tends to be bushy. However, it can tolerate gradual pruning to obtain a particular form (e.g., a shade tree).
Saplings will benefit from biannual applications of a balanced controlled-release fertilizer with minor elements, or monthly foliar feedings of an organic or inorganic water-soluble fertilizer diluted to ⅓ to ½ the recommended strength. Mature trees require little to no fertilizer.
Pests and Diseases
Hao has a white sap that seems to deter most insect pests. One exception is the Sphinx or Hawk Moth (We're not certain which species; there are several in Hawai‘i). The female Hawk Moth lays its green eggs on the leaves of the hao. There, they hatch, and the caterpillars rapidly consume the leaves. If you see this type of damage, you can easily remove the larvae by hand. Fortunately, the caterpillars do not eat the growing tips of the branches, so a new set of leaves quickly grows back after the caterpillars are gone. I (Koebele) have witnessed entire (small) hao rendered leafless by these caterpillars, but they have never killed a plant.
Additionally, hao is occasionally attacked by scale insects, which are often imported and protected by ants. Refer to the Pests & Diseases page for ways to eliminate or control these two pests.
Unfortunately, while I (Koebele) have propagated and planted out hao in both garden and restoration sites on O‘ahu for over 20 years, none of these plantings have lived past their 10th birthday. All of these mature hao gradually (over months) lost more and more of their leaves and then died. I know these premature deaths were not natural since I have visited wild hao that were well over 20 years old. To date (2025), I have been unable to determine the cause of these deaths, but suspect some type of root disease (maybe Fusarium wilt?) or pest (nematodes?) since I have not observed any cause above ground. If you have figured out the cause of these premature deaths, or have a cultivated hao over 15 years old, please contact us and share your mana‘o so we can edit this page and share your knowledge with others. You can contact us at: EickhoffandKoebele@gmail.com.
Uses
Ancient Hawaiian
Hao is still a relatively common tree in Hawai‘i making us believe the trees were even more common in ancient times. Why then are there so few records of the Hawaiians using this tree — surely it was good for something? Hao wood has been found in heiau, suggesting it had some unknown religious purpose [Lamb 1980]. But, other than this, reports about its use for construction and firewood are few and conflicting [Hawaiian Ethnobotany Online Database]. Unfortunately, we can’t go back in time to find the truth, but there is one clue as to why Hawaiians may have shunned this native plant. Hao, like its relatives, contains an alkaloid called reserpine, used in other parts of the world to treat high blood pressure and some mental diseases [Degener & Degener 1957].
Perhaps, the first Hawaiians to use hao (remember, hao is endemic to Hawai‘i) used it for a very common need, firewood. As the wood burned, the smoke containing the reserpine was likely inhaled by the nearby Hawaiians. This uncontrolled dose of reserpine might have had lethal or near-lethal effects, since reserpine lowers blood pressure by slowing the heart and dilating blood vessels. Or, maybe, the unlucky Hawaiians experienced some of reserpine’s mental side-effects such as dizziness and nightmares [MedlinePlus;Reserpine]. In any case, it seems likely Hawaiians quickly learned that burning hao could hurt them. And, perhaps, the use of hao was best left to their kāhuna (priests) within the confines of a heiau.
Modern
Special Features and Information
General
Apocynaceae is a large diverse group of trees, shrubs, herbs, succulents, and vines with a worldwide tropical, subtropical, and temperate distribution. Called the Dogbane family because some species members were used as dog poison. Its taxonomy has varied over the years; however, currently (2025) there are about 5,100 species within 376 genera [Wikipedia;Apocynaceae].
Other native Hawaiian plants in Apocynaceae include: four endemic species of hōlei (Ochrosia spp.); two endemic species of kaulu (Pteralyxia spp.), and the indigenous maile (Alyxia stellata). Hao flowers, though much smaller, resemble those of hōlei (Ochrosia spp.). Therefore, early taxonomists named it Ochrosia sandwicensis, which, today, is a synonym.
Hawaiian Name
Hao is also the word for iron and metal tools in Hawaiian [Pukui & Elbert 1986]. However, this is surprising since the wood of hao is relatively soft.
Etymology
Rauvolfia is named in honor of Leonhard Rauwolf (ca. 1540-1596), a German physician, botanist and traveler in the Near East [Wagner et al. 1990]. Interestingly, both Rauvolfia and Rauwolfia are acceptable names for this genus [Gledhill 2008]. The species name, sandwicensis, refers to the "Sandwich Islands," as the Hawaiian Islands were once called and named by James Cook on one of his voyages in the 1770s. James Cook named the islands after John Montagu (The fourth Earl of Sandwich) for supporting Cook's voyages [Gledhill 2008].
BPK