ʻApapane gray with small black eyes with a brown outline. The back of its wings and its tail are colored black, while back bottom is a grayish-white. Apapane are found in mesic and wet forests dominated by "ōhia lehua" ("Metrosideros polymorpha") and "koa" ("Acacia koa") trees. The best habitat also contains "kōlea lau nui" (" Myrsine lessertiana"), "naio" ("Myoporum sandwicense"), and "hapuu" ("Cibotium" spp.) tree ferns, while "māmane" ("Sophora chrysophylla") is a common species in high elevation foraging habitat. Most apapane are found at an elevation above , keeping the birds away from mosquitoes. It lives on the islands of Hawaii,
Acacia koa confirmed this close relationship; the estimated time of divergence is about 1.4 million years ago. "A. heterophylla" sequences nest within those of the more diverse "A. koa", making the latter paraphyletic. Both species are thought to be descended from an ancestral species in Australia, presumably their sister species, "Acacia melanoxylon". Dispersals most likely occurred via seed-carrying by birds such as petrels. Both species have very similar ecological niches, which differ from that of "A. melanoxylon". A closely related species, koaia or koaie ("A. koaia"), is found in dry areas. It is most easily distinguished by having smaller seeds that are