Acacia koa aka Koa

Acacia koa, or koa, is an evergreen Hawaiian tree. It belongs to the pea family, Fabaceae. Its native range covers six of the larger Hawaiian islands. It grows in mountain forests, both alone and with other trees. These include native ohia and mamane. Koa forms part of the forest canopy across varied habitats. Useful Tropical Plants reports its conservation status as Least Concern.

Koa grows fast and forms a broad, dense crown. Garden trees reach about 50–80 feet (15.2–24.4 metres) tall. Their spread can reach 40 feet (12.2 metres). Some trees reach 100 feet (30.5 metres). Useful Tropical Plants reports extremes of about 115 feet (35 metres). Other populations stay smaller and take a shrub-like form. Trees grown in open ground spread widely. The trunk may grow crooked rather than straight. Young bark starts smooth and reddish brown. With age, it gains ridges, furrows, and pale scales.

Young foliage has twice-divided leaves with many small leaflets. Mature trees bear stiff, dull green phyllodes instead. These flat leaf stalks take on the work of leaves. They curve like a sickle and have parallel veins. Some still carry divided leaflets. Slender twigs zigzag and change from green to gray-brown. They lack thorns and spines. Small, round flower heads range from yellow to white. Flowers appear year-round, with the main flush in late winter. Bees pollinate them, and the tree can self-fertilise. Flat pods turn from green to dark brown as they ripen. Each pod holds six to twelve seeds. Pods can ripen throughout the year.

Koa needs full sun and soil that drains well. It grows best in medium to strongly acid soil. It does well where rainfall is high. Garden guidance gives it a medium water need. Missouri Botanical Garden lists USDA hardiness zones 10–11. Growers usually raise new trees from seed. Its broad crown suits large landscapes in subtropical areas. Gardeners have also grown it in parts of California. Its flowers attract butterflies, while evergreen foliage adds winter interest.

Koa provides timber for furniture, veneer, and crafts. Plantings also restore native tree cover on damaged land. Missouri Botanical Garden reports few major pest or disease problems. Yet koa moth can cause serious damage. Twig borers, fungi, and koa wilt also need watching.