Acacia koa is the largest of the native Hawaiian trees. It is found only on the Hawaiian islands (endemic). The bark is mottled reddish and gray. Small yellow flowers cluster in balls and are found in the axils of the leaves (where the leaves meet the branch). Young Acacia koa trees have leaves with 12-24 oval-shaped leaflets. Mature trees have long (3-10 in), sickle-shaped, flattened leaf stalks that look like leaves, called phyllodes, that are not true leaves. The combination of the long phyllodes and the pale yellow flowers distinguish Acacia koa from other aiian trees.
Acacia koa is a very important tree for Hawaiians. Historically, these trees were used for creating canoes and the wood is used for timber, furniture and other uses. It is one of the most expensive woods in the world. The tree is often found in pastures and agricultural lands but is not as abundant as it once was. Efforts are underway to plant more of these trees on the islands. Acacia koa trees are also important for creating habitat for birds and insects.