Greater koa finch below. It had a thick black bill which allowed it to break open seed pods that were found in the trees. In historical times, its range was largely confined to the Kona District of the island of Hawaii, although it was observed in the Kīlauea area in 1895. It was much more widespread prior to the arrival of humans in Hawaii, and related species lived on other islands. In Kona, it co-occurred with the closely related lesser koa finch ("Rhodocanthis flaviceps"), and the Kona grosbeak. The lesser and greater koa finches were once thought by scientists to be the minimum
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