Acacia koa for up to 25 years. Scarification is needed before "A. koa" seeds will germinate. Koa is endemic to the islands of Hawaii, Molokai, Maui, Lānai, Oahu, and Kauai, where it grows at elevations of . It requires of annual rainfall. Acidic to neutral soils (pH of 4-7.4) that are either an Inceptisol derived from volcanic ash or a well-drained histosol are preferred. Its ability to fix nitrogen allows it to grow in very young volcanic soils. Koa and ōhia lehua ("Metrosideros polymorpha") dominate the canopy of mixed mesic forests. It is also common in wet forests. The koa's trunk was
Koa people as the centre, they extended north as far as Kynuna. Their western boundary lay around Middleton Creek, wshile to the east, their frontier was at Winton and Sesbania. Their southern limits were around Cork. Neither circumcision nor subincision played any part in the Koa's initiatory rites into manhood. At least one Koa Bora ground, a gibber clearing threaded with portoluca, used to exist close to the homestead on Carisbrooke Station, southwest of Winton. Comparatively little is known of the Koa, and, in one modern tradition of whites in the area, they just 'melted away' when Europeans began to settle in