Koa (Acacia koa) is a tropical hardwood that is native to the Hawaiian Islands and the only place it grows in quantity. Koa seems to have no preference as to soil or climate, because it grows from the beaches to volcanic peaks in Hawaii. Koa is one of Hawaii's largest trees, which grow to 120 foot tall and up to 10 feet in diameter at maturity, and has often been called "King of the Hawaiian Woods.” The straight trunk of the Koa has a flaky, fissured bark that appears gray in color.

The branches, which may be as far as 80 feet from the ground, exhibit small light-green, pointed leaves in clusters. Koa leaves are unusual in that the juvenile plants immature leaves, or first leaves, are not only different but are also compound leaves look totally different than the crescent shape leaves of a mature plant, which are not compound. The mature Koa leaves are flat and strong. Because dry Koa leaves tend to resist water, they can be very slippery to walk on.

The flowers of the Koa are small yellow and puffball like. 

For centuries, natives of Hawaii hollowed out huge outrigger canoes from the Koa logs, which, are resistant to salt water, making them perfect for boat building. They used these canoes to travel hundreds of miles from island to island for war or trade. They honored this sea-worthy wood with the name Koa-ka, which means Valiant Soldier.  The English shortened the name to Koa.

            Missionaries returning to the U.S. ports, bought items made of Koa in the late 1800's, which created demand for logs by craftsmen who were furniture makers, coachbuilders and even architects, but no one sang praises of the Koa’s gorgeous wood as loud as the Hawaiian’s did. Hawaiian craftsmen created ukuleles from Koa, an instrument introduced by the Portuguese sailors.

            Early in the 1970's Koa was easy to acquire, in the U.S. mainland, but then nearly disappeared from the markets due to Hawaii’s main Koa mill closing. Since then, small mills have made the beautiful Koa wood available again.

            Today, the Koa tree is a protected tree in Hawai'i. You can find Koa all over the Big Island, but huge stands of Koa are easy to find in the Volcano area, including Bird Park and the National Park itself. Because the wood is so prized for all sorts of uses, some of which include gunstocks, fine furniture, sculptures, musical instruments, boat trim, and wood turnings such as handmade wood pens and toys, it is now illegal to kill any living Koa tree, and only dead trees may be used for any type of woodworking.

In Ancient Hawaiian Medicine, Both the bark and the crescent leaves of the Koa were used in various medicinal preparations including birth control.