The Maui Nukupuu (Hemignathus affinis Rothschild) was historically known only from the island of Maui, yet, this species or at least a very closely related one also once inhabited the neighboring island of Moloka’i – and very likely also Lana’i.:
“A fossil almost certainly of this species [Hemignathus lucidus Lichtenstein] was also recovered from sand dune deposits on Molokai.” 
Given the fact that the Amakihi (Hemignathus virens (Gmelin)) is known to have inhabited the island of Hawai’i (with the nominate form) as well as the islands of Lana’i, Maui, and Moloka’i (with another subspecies), it is quite certain that the Molokai Nukupuu was identical with the Maui species, perhaps even on subspecific level.
All species formerly known as Nukupuu are now extinct.
 Storrs Olson & Helen F. James: Nomenclature of the Hawaiian Akialoas and Nukupuus (Aves: Drepanidini). Proceedings of the Biological Society of Washington 108(3): 373-387. 1995
The drepanidine genus Hemignathus contains up to 16 species, depending on which author, which sometimes are named as ‚little green birds‘ colloquially, relating to the mainly olive green color of most of these species.
The genus is divided into four subgenera; Akialoa (large species with unusual long, downwardly bent beaks), Chlorodrepanis (small species with short, slightly bent beaks), Hemignathus (species with strongly downwardly bent beaks and the maxillary about twice the length of the mandibular beak), and Viridonia (a single species with a straight beak, actually not closely related to the other species).
The Hawaiian name Nukupu’u literally means ‚nose [formed like a] hill‘ and relates to the form of the beak; the three species named as Nukupu’u (Hemignathus affinis, Hemignathus hanapepe Wilson, Hemignathus lucidus Lichtenstein) all shared downwardly bent beaks with a maxillary about twice as long as the mandibular beak. The birds used these strange beaks to probe the crevices of tree bark for insects and insect larvae.
The Maui Nukupuu was last seen in 1967 in the Kipahulu Valley in the southeastern part of Maui – since then the species is considered extinct.
The Maui Nukupuu, respectively perhaps a subspecies of it, is known also from subfossil remains found on the island of Moloka’i, Maui’s neighbor. 
 W. E. Banko: Rediscovery of Maui Nukupuu, Hemignathus lucidus affinis, and Sighting of Maui Parrotbill, Pseudonestor xanthophrys, Kipahulu Valley, Maui, Hawaii. Condor 70: 265-266. 1968  D. Luther: Die ausgestorbenen Vögel der Welt. Westarp Wissenschaften 1986  H. D. Pratt; P. L. Bruner; D. G. Berrett: A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press 1987  E. Fuller: Extinct Birds. Penguin Books (England) 1987  S. L. Olson; H. F. James: Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part II. Passeriformes. Ornithological Monographs 45: 1-91. 1991  Storrs L. Olson; Helen F. James: A specimen of Nuku pu’u (Aves: Drepanidini: Hemignathus lucidus) from the island of Hawai’i. Pacific Science 48(4): 331-338. 1994  H. D. Pratt: The Hawaiian Honeycreepers: Drepanidinae. Oxford Univ. Pr. 2005  J. P. Hume; M. Walters: Extinct Birds. Bloomsbury Publishing Plc 2012