Гавайи ағашы: Коа ағашының сипаттамасы мен маңызы

Species of flowering tree endemic to the Hawaiian Islands

Acacia koa, commonly known as koa, The highest populations are on Hawaii, Maui and Oahu.

The name koa in the Hawaiian language ultimately comes from Proto Austronesian *teRas meaning "core" or "ironwood"; many names referring to certain ironwood or heartwood species in Southeast Asia and Oceania such as Vitex parviflora (tugás in Cebuano), Eusideroxylon zwageri (togas in Tombonuwo), and Intsia bijuga (dort in Palauan) descend from this root. Koa also means brave, bold, fearless, or warrior.

Koa is a large tree, typically attaining a height of and a spread of In deep volcanic ash, a koa tree can reach a height of , a circumference of , and a spread of It is one of the fastest growing Hawaiian trees, capable of reaching in five years on a good site.

Initially, bipinnately compound leaves with 12–24 pairs of leaflets grow on the koa plant, much like other members of the pea family. At about 6–9 months of age, however, thick sickle shaped "leaves" that are not compound begin to grow. These are phyllodes, blades that develop as an expansion of the leaf petiole. The vertically flattened orientation of the phyllodes allows sunlight to pass to lower levels of the tree. True leaves are entirely replaced by long, wide phyllodes on an adult tree. Flowering may be seasonal or year round depending on the location. Its ability to fix nitrogen allows it to grow in very young volcanic soils. It is also common in wet forests.

The koa's trunk was used by ancient Hawaiians to build waa (dugout outrigger canoes) and papa hee nalu (surfboards). Only paipo (bodyboards), kikoo, and alaia surfboards were made from koa, however; olo, the longest surfboards, were made from the lighter and more buoyant wiliwili (Erythrina sandwicensis). The reddish wood is very similar in strength and weight to that of Black Walnut (Juglans nigra), with a specific gravity of 0.55, often used in the construction of ukuleles, acoustic guitars, and Weissenborn style Hawaiian steel guitars. B. C. Rich used koa on some of their electric guitars as well, and still uses a koa veneered topwood on certain models. Fender made limited edition koa wood models of the Telecaster and the Stratocaster in 2006. Trey Anastasio, guitarist for the band Phish, primarily uses a koa hollowbody Languedoc guitar. Commercial silviculture of koa takes 20 to 25 years before a tree is of useful size. Taylor, Collings and Martin are few among the many other brands that use that tonewood for manufacturing acoustic guitars.

Among other Pacific Islands of volcanic (non continental) origin, only Vanuatu has native Acacia species. A. heterophylla, from distant Réunion, is very similar and has been suggested to be the closest relative of koa. Genetic sequence analysis results announced in 2014 confirmed this close relationship; the estimated time of divergence is about 1.4 million years ago. A. heterophylla sequences nest within those of the more diverse A. koa, making the latter paraphyletic.

Koa is the preferred host plant for the caterpillars of the green Hawaiian blue (Udara blackburni), which eat the flowers and fruits. Adults drink nectar from the flowers. Koa sap is eaten by the adult Kamehameha butterfly (Vanessa tameamea). The koa bug (Coleotichus blackburniae) uses its rostrum to suck the contents out of koa seeds. Koa is vulnerable to infection by koa wilt.