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Hawaiian wiliwili tree is making a comeback

February 2, 2014 - 8:10am

The Hawaiian wiliwili is coming back. Though this attractive dryland forest tree was severely threatened by the arrival of the invasive erythrina gall wasp, Quadrastichus erythrinae, that arrived in Hawaii around 2005, the tree’s plight is improving. A predator of the African pest was introduced in Hawaii and seems to be doing its job well.

Wiliwili, Erythrina sandwicensis, is an endemic Hawaiian dry forest tree in the Fabaceae or Legume family. It can serve as a striking specimen in a landscape. It has an interesting growth habit, lovely flowers and spiraling seed pods that reveal bright orange seeds. Its tolerance for long, dry periods makes it an excellent selection for a xeriscape.

Several other Fabaceae family trees that can be found in Hawaii nurseries are also commonly known as wiliwili. The upright ornamental E. variegata, “tropic coral,” serves as a wind break in many locations and was also adversely affected by the gall wasp. The Indian coral tree, another E. variegata, is native to India and sometimes referred to as wiliwili haole. Anenanthera pavonina, also in the Legume family, is a Southeast Asian native that is larger than the Hawaiian wiliwili but sometimes referred to as false wiliwili. Only the E. sandwicensis is native to these islands.

The native wiliwili was originally established at lower elevations on the dry leeward sides of all the major Hawaiian Islands. The generic name, erythrina, is from the Greek erythros, which translates to “red,” referring to the color of some of the species’ flowers. Sandwicensis is a reference to the Sandwich Islands, a name applied to Hawaii by Captain James Cook. Wiliwili literally means twist-twist in Hawaiian and refers to the seed pods which twist open exposing the seeds.

In its preferred habitat, wiliwili can grow to 40 feet, but in a tended landscape it often ranges between 20 and 30 feet. The bark is rough and reddish with spines and often appears yellow from a distance. The leaves are wider than long, oval in shape, smooth on the upper surface and hairy on the lower surface. They are usually grouped in threes and range between 1 and 4 inches long. Like several of its cousins, wiliwili is deciduous.

In West Hawaii, the tree usually loses its leaves in late summer or early fall and puts out a gorgeous display of blossoms on the leafless tree. In a dry Kona year, the tree will sometimes flower in mid-winter. The flowers are usually orange but sometimes appear in white, yellow or chartreuse. Bishop Museum’s ethnobotany data reports that when the wiliwili blooms, the shark bites. Investigation of these coincidental events has not been fully researched, however. The seed pods that follow flowering contain one to three red-orange seeds that resemble beans.

Wiliwili trees grow best in dry landscapes, in full sun and with good soil drainage. Their native habitats are often rocky and hot. They will do best in similar conditions when installed in a landscape.

Many parts of the wiliwili tree are culturally useful. Its lightweight wood was often used by the early Hawaiians for surfboards for the alii. The wood was also used on canoes for the ama and for fishing net floats. Wiliwili seeds and flowers are still used in lei making.

Wiliwili trees attract a wide range of pollinators including many species of birds, butterflies, moths and bees. Research suggests that the most frequent pollinator for wiliwili today is the Japanese white eye. This small bird is probably attracted to the nectar in the wiliwili flowers as well as the insects it attracts.

Wiliwili is easily propagated from seeds or cuttings. If you want a short wait to flowering and a specific flower color, vegetative propagation works best. Start by taking a cutting of 4 to 8 inches from an actively growing branch and remove all but the terminal leaves. Dip it in a rooting compound and bury the bottom half of the cutting in a rooting medium containing perlite, vermiculite or peat moss. Cuttings will do best in a medium that dries out between waterings and is located in bright light but not direct sunlight. They may take several months to root, so be patient.

Seeding wiliwili often yields better results. Place the seeds you collect in water and only use those that sink. You can store dry seeds in the refrigerator for many years if you like. A few days before planting, soak the seeds and scarify them to break the seed coat to quicken germination. Plant them about 1 inch deep in a sterile media. Healthy seeds will germinate within a week and can then be placed in a sunny spot. After about a month, lightly fertilize the seedlings to encourage growth. In another month or two, once several leaves and some bark have developed, you can plant the seedling in your garden and water it once a week. After a month or two, stop watering it.

Wiliwili grow quickly and can reach 6 feet tall within a year, though they may not flower or produce seeds until their fifth year. They lose their leaves in dry weather, so don’t panic when they do.

You can prune your tree to shape it and keep it small, but pruning is not necessary. Wiliwili trees are natural nitrogen fixers so they do not need added fertility, though a triple-8 applied occasionally will not hurt.

In addition to the gall wasp, three other pests are worth noting. Chinese rose beetles can chew holes in leaves while spider mites and powdery mildew can cover leaves with a white webbing or grey powder, respectively. These pests are easy to control and though they may make the tree unsightly; they usually do not kill it.

Several efforts at preservation of native dryland forest species have led to preserves that include wiliwili as well as endangered native Hawaiian plants. The Waikoloa Dry Forest Initiative manages a preserve near Waikoloa Village where protection from feral ungulates and elimination of grasses that encourage fires are being practiced. More information about this project is available at waikoloadryforest.org.

You can learn more about the wiliwili and other dryland forest species at the upcoming Dryland Forest Symposium scheduled Feb. 21 at King Kamehameha’s Kona Beach Hotel. Go to drylandforest.org/2014-n%C4%81helehele-dryland-forest-symposium for more information.

You can learn about wiliwili at Amy B.H. Greenwell Ethnobotanical Garden in Captain Cook. They also have trees for sale.

The information in this column was reviewed for accuracy by Peter Van Dyke, director of Amy B.H. Greenwell Ethnobotanical Garden in Captain Cook.

Diana Duff is an organic farmer, plant adviser and consultant.