Kleidervögel
It was dissimilar to other Hawaiian birds; evidence based on DNA analysis supports it as being the most ancient of all the Hawaiian honeycreeper lineages to survive to recent times, its lineage having split off from the rest of the Hawaiian honeycreepers during the late Miocene, about 5.7-5.8 million years ago. The Hawaiian honeycreeper lineage itself only diverged from its common ancestor with "Carpodacus" around 7.2 million years ago; this would make the divergence of the poouli chronologically closer to the initial divergence from the common ancestor with "Carpodacus" than to the divergence of most other Hawaiian honeycreeper lineages (aside from the one containing "Oreomystis" and "Paroreomyza", which diverged about a million years after "Melamprosops"'s lineage), most of which diverged after the mid-Pliocene, 3.77 mya. Around the time the poouli lineage originated, Ni'ihau and Kauai were the only two large Hawaiian islands in existence (aside from the then-larger Northwestern Hawaiian Islands), indicating that the po'ouli's lineage most have evolved there and eventually spread to Maui Nui at some point after it first arose in the early Pleistocene, with the recent poouli evolving on and/or eventually becoming restricted to Maui.