The koaia or koaie (Acacia koaia; Family Fabaceae) is a small tree endemic to the Hawaiian Islands. It is closely related to the koa, and is sometimes considered to be the same species. The koaia is usually distinguished by growing as a short, broad, knarled tree; having the seeds longitudinally arranged in the pod; shorter, straighter phyllodes; and much denser wood. A population on the northern coast of Kauai may be intermediate, but the relationships have not been worked out. Koaia wood is claimed to be very different from that of koa, and this may be the best character to separate them.
Koaia is highly adapted to dry habitats, and is capable of forming dense forests in areas with very little rainfall. It was formerly found widely in dry forest on the islands of Hawaii, Maui, Molokai, and Lānai, and Oahu. However, it has been devastated by cattle and other ungulates and is now rare. It can be seen on ranch land in North Kohala, and at a small fenced exclosure outside of Waimea known as the koaia sanctuary.