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
Oʻahu ʻamakihi assigned to "Chlorodrepanis" based on the phylogenetic analysis of mitochondrial and nuclear DNA sequences. It tends to stay in the wetter southern area of Oahu, and in the valley near Wahiawa and Mililani. It can easily be spotted in two major parks, the Honouliuli Preserve, and the Wa'ahila Ridge State Recreation Area. It tends to stay in forest, but has - at least to some extent - adapted to non-native forest types. It will nest and forage in wooded urban areas, but prefers native habitats where koa ("Acacia koa") dominates. It mainly occurs at altitudes above , but in some