Native Plants of Hawai‘i - Erythrina sandwicensis

Erythrina sandwicensis

Fabaceae or Pea family

Synonyms: Corallodendron monospermum, Erythrina monosperma, Erythrina sandwicensis f. alba, Erythrina sandwicensis f. lutea, Erythrina sandwicensis var. luteosperma

Wiliwili

Hawaiian coral tree

Hawaiian erythrina

Natural Range & Environment

Erythrina sandwicensis is endemic to all the main Hawaiian Islands, where it is found from sea level to about 600 m (1,969 ft) in open and closed dry forests [Wagner et al. 1990].

Two of many wiliwili flower color variations. A healthy leaf (with three leaflets). Erythrina gall wasp damage to leaves at stem-tip. A young cultivated tree with leaves. Wild mature tree blooming on Maui. (Flower colors, healthy leaf, cultivated and wild tree photographs all courtesy of Forest & Kim Starr CC BY 3.0). Header photograph of seeds in open pods.

Description

Erythrina sandwicensis is an at-risk small to large (up to 60 ft [18 m] tall) tree with a lifespan greater than five years. Wiliwili is one of the few deciduous trees native to Hawaiʻi. In the wild, trees have an annual blooming/foliage cycle. Leafless, they flower from late summer to early fall. Then, in late fall to early winter (often after the first rains), they flush with new leaves only to start dropping their leaves again in spring (presumably to conserve water during the hot dry summer).

Wiliwili bark is yellow through orange to light green and papery, while the wood is white to yellow and very lightweight. Most wiliwili have thorns, but there can be considerable variation between trees, with some being nearly thornless while others are a treehugger's nightmare. Mature leaves are 1 to 4 inches (2.5 to 10 cm) long with three leaflets and have a smooth upper surface and hairy undersurface. New leaf buds are often covered in a dense fuzz. The perfect (bisexual) flowers are pea-like, clustered on a stalk, and can be white, greenish-white, yellow, orange, or light red; orange is the most common color. Some flowers can even be a mix of two or more colors. Wild populations may have a variety of different flower-colored trees or all the same color. Ripe seedpods are fuzzy, light brown, and contain one to four seeds. The seeds are bean-like, can vary in size and color from yellow to dark red, and are thought to be poisonous [Little & Skolmen 1989], although we don't know of anyone brave/foolish enough to confirm this.

Growth Requirements

General

Erythrina sandwicensis can grow in very harsh environments where few plants can survive. They are tolerant of extreme heat, drought, and strong winds, as well as significant damage (e.g., a truck backing into a wiliwili and severely damaging its trunk). Therefore, it's a shame that alien coral trees, particularly Erythrina variegata (Indian coral tree) and E. crista-galli (Cock's spur coral tree), sometimes improperly called wiliwili, were/are planted more frequently in parks and urban landscapes than our native wiliwili. Some cite wiliwili's thorns as being the reason for their scarcity in cultivated settings. However, wild populations of wiliwili vary greatly in how thorny they are, particularly when mature; admittedly, most young wiliwili are indeed thorny. Given that the more popular alien Erythrina are also thorny in the wild, and only our artificial selection was responsible for "taming" these trees, why can't we do the same with our native wiliwili?

Use wiliwili as a single focus tree, or plant them en masse to fill a large space. Wiliwili can also be kept as a container plant in a bonsai fashion, but this requires more maintenance.

Erythrina sandwicensis grows best in a site with full sunlight in a variety of soils (i.e., coralline, lava/cinder, clay, organic-dominant), provided there is good drainage. Plant your wiliwili seedling in the ground when you see bark developing on its trunk; green-trunk seedlings are more vulnerable to attacks by snails, slugs, insects, fungi, etc. Water the new planting initially once a week for a month or two, and then stop. Your wiliwili should then be watered only occasionally, if at all. Remember, this is a dry forest tree, and if you water it too often, you’re likely to kill it by encouraging fungal or bacterial diseases to attack its roots and trunk. Young potted plants before planting will grow better with low doses of a water-soluble organic or inorganic fertilizer applied regularly; avoid fertilizing during the summer months when the plant goes partially dormant. However, once in the ground, no additional fertilizer is needed for these nitrogen-fixing trees.

In the ground, wiliwili often grow fast and can reach six feet (2 m) in height in less than a year. However, they normally take several years to mature, so don’t expect to see flowers until about the fifth year in the ground. It is normal for wiliwili to lose all or most of its leaves during the dry summer months; the natural rest permits the tree to eliminate any pests that may be attacking its leaves. However, if you just can’t bear to see your tree without leaves, you can (sparingly) water it during these dry months, tricking the plant into retaining at least some of its leaves.

Pests and Diseases

With its discovery on Oʻahu in April 2005, the tiny alien Erythrina gall wasp (Quadrastichus erythrinae) became a serious pest, greatly affecting (i.e., killing or preventing flowering and leafing) many populations of wiliwili and other non-native Erythrina species throughout the State. In November 2008, the State, after carefully testing, released a few thousand Tanzanian parasitoid wasps (Eurytoma erthrinae), which specifically attack the Erythrina gall wasp, on most of the main Hawaiian Islands with the hope of saving these beautiful trees. Most recent reports indicate these efforts have been successful, and today the two insects live in a predator-prey balance [DLNR;HISC]. Also, check out the animated educational video, produced by the Coordinated Group and Alien Pest Species (CGAPS) and the Department of Land and Natural Resources (DLNR), entitled Wiliwili Trees in Hawaiʻi: A Biocontrol Success Story at BiocontrolHawaii.org, or on YouTube or vimeo.

Even though we now have an ally in the fight against the Erythrina gall wasp, that doesn’t mean it has disappeared. The first damage normally appears near the growing tips. If you cannot wait for the parasitoid wasps to show up, you can try to minimize the damage by treating your wiliwili with a systemic insecticide.

Four other wiliwili pests worth noting are the Chinese rose beetle, cottony cushion scale, spider mites, and powdery mildew (a fungus). Rose beetles chew holes in the leaves while spider mites and powdery mildew cover the leaves with a white webbing or powder, respectively, that eventually kills the leaf. Cottony cushion scale infests stems and leaves, sucking sap from the tree. All of these pests make a tree unsightly, but normally do not kill it. Refer to the Pests & Diseases page for ways to deal with each of these pests.

Uses

Ancient Hawaiian

The lightweight wood of wiliwili was the preferred choice for surfboards (papa heʻe nalu), both long (alaia) and short (olo). However, since large straight trees suitable for longboards may have been difficult to find, they were likely reserved for nobility. The wood was also typically used on outrigger canoes (waʻa) for the float (ama), for net floats, and for fishing gear containers which would float if the canoe was upset [Buck 1957; Neal 1965; Abbott 1992]. Seeds were strung into permanent lei, while flowers were used for temporary lei [Abbott 1992; McDonald & Weissich 2003]. According to Kaʻaiakamanu & Akina [1922], flowers or pounded bark were used to treat various venereal or genital diseases.

Modern

Today, wiliwili seeds and flowers are still used to make lei [McDonald & Weissich 2003].

Special Features and Information

General

The Pea family (Fabaceae) is a large (i.e., third-largest behind Orchidaceae and Asteraceae) and agriculturally important plant family with about 20,000 species within 765 genera. Members display a wide variety of growth forms (i.e., trees, shrubs, herbs, vines, lianas) with many species hosting nitrogen-fixing bacteria within root nodules [WikipediA;Fabaceae].

Wiliwili is the only native member of Erythrina in Hawai‘i, a genus of about 130 species worldwide, collectively known as coral trees [Wikipedia;Erythrina].

There are many mo‘olelo (stories) and sayings (‘ōlelo no‘eau) concerning wiliwili. Here is one of each:

Four sisters once lived in Ka‘u on the Big Island. The first, whose name was Moholani, was very beautiful. Unfortunately, the second sister was bald, the third was humpbacked, and the fourth had ragged, wind-tossed hair.

Beautiful Moholani married and had a son who was given to the gods to raise. One day Moholani’s husband was lured out to sea by some pretty sirens. Frantically, Moholani asked her sisters to help find her errant husband. But they refused, calling him worthless. This aroused the wrath of Moholani’s son who sent lightning to transform the sisters into wiliwili trees. The bald sister became a wiliwili with few leaves, the humpbacked sister a gnarled wiliwili and the wind-tossed sister a wiliwili with leaves that flutter in the breeze. Thus chastened, Moholani’s husband returned, never to stray again. That, according to Hawaiian legend, is how the wiliwili tree came to be. [Taken from Majesty The Exceptional Trees of Hawaii, published by The Outdoor Circle, 1982.]

Pua ka wiliwili nanahu ka manō; pua ka wahine u‘i nanahu ke kānāwai. (When the wiliwili tree blooms, the sharks bite; when a pretty woman blossoms, the law bites.) [Taken from ‘Ōleleo No‘eau Hawaiian Proverbs & Poetical Sayings by Mary Kawena Pukui, 1983.]

Good advice for both young men competing for a beautiful woman and surfers who need to know how to tell the difference between the true Hawaiian wiliwili and the introduced Erythrina, often incorrectly called wiliwili. The true wiliwili flowers in late summer and early fall when the ocean is warm and the sharks are mating (and aggressive). In contrast, the most commonly introduced Erythrina, Erythrina variegata, flowers during the winter months.

Hawaiian Name

Wili translates as "to twist, screw or wind," while wiliwili means "very twisted" or "repeatedly twisted," referring to the ripe seed pods that twist, split open, and expose the brightly colored seeds [Pukui & Elbert 1986].

Etymology

Erythrina is from the Greek word erythros, meaning "red," in reference to the flower color of many species [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 to honor John Montagu (The fourth Earl of Sandwich) for supporting Cook's voyages [Gledhill 2008].

BPK