The Hawaiian wood commonly known as Koa is known to botanists and other scientists as Acacia koa.
The range of A. koa extends from longitude 154° to 160° W; its latitude ranges from 19° to 22° N. It is found on all six of the major islands of the Hawai’ian chain: Hawaiʻi, Molokaʻi, Maui, Lānaʻi, Oʻahu, and Kauaʻi, while the largest populations are found on Hawaiʻi, Maui, and Oʻahu.
A. koa trees are found nowhere else in the world outside of these six geographically isolated islands.
A closely related species Acacia koaia is found in dry areas of the Hawai’ian Islands, but as it has been much more heavily impacted and damaged by the cattle industry, it is now rare. The most significant remaining stocks of this rare tree can be seen in the remote North Kohala region found on the far northeast coast of the main island, Hawai’i. The wood of A. koaia is denser, harder, and more finely grained than A. koa wood.
The only other Pacific islands that support an endemic Acacia species are the islands of the nation of Vanuatu, formerly known as the New Hebrides while under the joint rule of France and the United Kingdom.
The species most closely related to A. koa is A. heterophylla, from the incredible distant island of Réunion located in the southern Indian Ocean, relatively close to the mega-island of Madagascar.
Acacia species are most common in Australia and it is believed that both A. koa and A. heterophylla are descended from Acacia melanoxylon, commonly known as Australian Blackwood.
The incredibly wide dispersal range is believed to be the result of seed carrying by long distance flying ocean birds such as the petrel. Both A. koa and A. heterophylla prosper in similar environments, which are very different from the environment favored by the presumed parent species A. melanoxylon.
A. koa is a nitrogen fixing plant and as such it is one of earliest colonizers of lava flow areas as it thrives in this hard and acidic soil, promoting the breakdown of the lava into fertile soils through the addition of nitrogen which makes it a vital component of the ecology of volcanic islands.
A very detailed analysis of Koa ecology is available at no charge from the Pacific Southwest Research Station of the Forest Service under the auspices of the United States Department of Agriculture.
For the sake of simplicity and common understanding, from this point forward I will refer to A. koa by its common name of Koa. Some sources refer to Koa by the redundant Hawai’ian Koa but I will use the simpler form.
The color of Koa wood is quite variable but in general most samples tend to be of a medium golden or reddish brown color. Many people consider the color to be similar to true Mahogany of the Swietenia sp, most of which is heavily over-exploited and vigorously protected.
One reason for the wide appeal of Koa is due to the common presence of contrasting bands of color in the growth rings which create a very attractive and unusual visual appearance when compared to woods of similar color. An even more desirable color characteristic is the appearance, again not uncommonly, of boards with distinctive ribbons or streaks of color.
But the most desirable and therefore the most potentially astronomically expensive pieces of Koa are those with pronounced wavy and/or curly grain patterns. These patterns in Koa in particular are not especially rare but as overall supplies of Koa are limited, those pieces with pronounced figure are especially prized by users for many different purposes, but especially for use as tonewoods in very high-end stringed instruments ranging from guitars to ukuleles.