Native Hawaiian Garden (7722)

Hao (Rauvolfia sandwicensis) – If only we had a time-machine.

Hao is still a relatively common tree in the remnant dry forests of Hawai‘i making us believe the trees were even more common in ancient times. So, 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. But, other than this, reports about its use for construction and firewood are few and conflicting. 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). Maybe, 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. 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 kahuna (priests) within the confines of heiau.

Habitat & Appearance: Wagner et al. (1990) state hao is found primarily in mesic forests and even wet forests. However, this is not my experience. My observations suggest hao’s habitat is lowland dry forest and, occasionally, in the gulches of dry shrublands. It grows on all the main islands except Kaho‘olawe. Hao is an attractive tree with shiny light green leaves with a yellow midrib. The bark is nearly white and as it gets older acquires a bumpy texture. Hao are not very big. For the first ten years, you can expect them to be less than 15 feet tall. Old trees may be about 30 feet in height. Hao produces small white flowers in small clusters that are very fragrant; hao is a relative of plumeria. It’s a pity the flowers are not plumeria-sized. If they were, I would guess, hao would be a more commonly cultivated tree.

When collecting, a net bag around the unripened hao fruits works well to deter birds and rats which love the ripe fruit and seed, respectively. Hao seedlings at different stages. A five-year-old hao surrounded by ‘ilie‘e. Header photograph courtesy of Forest & Kim Starr CC BY 2.0.

Hao in Hawaiian Culture: See above.

Collecting Seeds: 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, they can flower and fruit more than once each year. Hao fruits are about the size of a grape but are often bilobed containing two seeds. The seeds are mature when the fruit is dark purple or black and soft. Sometimes you can find viable seeds in the soil below the tree. Test these by seeing if they float or sink in water; the viable seeds will sink. Unfortunately, nearby rats often crack open and eat the seeds so that all you find are piles of seed-halves. Seeds remain viable in a refrigerator for at least five years.

Growing from Seed: If your fruits or seeds were collected from the ground be sure to clean and sterilize them before sowing. Using either Method One or Two, hao seeds begin germinating in about two months and can continue sprouting for several months. The seedlings grow rapidly in the nursery and should be 10 inches tall in 3-6 months. They can be planted out at this height. In the nursery, the seedlings are normally pest-free although I have had a few die quickly, I believe, from overwatering.

Growing from Cuttings: I’ve never tried to grow this plant from cuttings but I’ve been told it’s possible.

Growth in the Garden: Hao requires a little more water than wiliwili, ‘a‘ali‘i, and naio to grow quickly and vigorously. However, like many other dry forest plants, you really don’t have to water hao after it reaches about two feet in height. After five years, maybe sooner with watering and fertilizer, your hao should be about ten feet tall and flowering. The plant does best in full sun and will look a bit spindly if planted in constant shade. Trees in the open tend to be bushy. However, with some pruning of the lower branches, it’s possible to shape your hao into an excellent shade tree.

Diseases & Pests: Hao has a white sap that seems to deter most insect pests. One exception is the Sphinx or Hawk Moth (I’m 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 pests are gone. I have witnessed entire (small) hao rendered leafless by these caterpillars, but they have never killed a plant.

Unfortunately, while I have propagated and planted out hao in both garden and restoration sites for over 20 years, none of these plantings have lived past their 10th birthday. All 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 are well over 20 years old. To date (2022), I have been unable to determine the cause for these deaths, but suspect some type of root disease or pest since I have not observed any cause above ground. Refer to my discussion on this topic in my introduction to ‘ohai.

Ā ā Ē ē Ī ī Ō ō Ū ū