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 wilt to the Hawaiian islands. It ranges in size from 15 to greater than 50 feet with a canopy spread of 20 to 40 feet. It has a showy white flower and blooms sporadically. Mature leaves are sickle shaped. Koa wilt is typically a fatal pathogen for its host. In only a few months, a tree may lose its entire canopy and die. Trees less than fifteen years old are typically the most susceptible. Symptoms include stains in cambium, roots, and sapwood as well as chlorosis (yellowing), canopy dieback, brown and wilted leaves, oozing sap, and bark cankers. The Koa wilt