In 1888 Sir Walter Buller opposed his fellow ornithologists in asserting that piopio belonged to a distinct evolutionary lineage. He opted to make Turnagra the type of a new family, Turnagridae.
Questions surrounding the taxonomy and evolutionary relationship of the piopio are still hotly debated, but recently:
Historically, the genus Turnagra has been placed within several different families and often as a genus ‘incertae cedis’ near the Pachycephalinae - an ancient Australo-Papuan radiation of songbirds known as the whistlers.
However, a DNA study by Christidis et al (1996) provided evidence that Turnagra was basal to the bowerbirds and suggested that it be retained in its own family and placed in sequence before the bowerbirds, Ptilonorhynchidae (Gill, 2010).
The most recent published taxonomy for the group is as arranged in Gill (2010):
†Turnagridae Buller, 1888: History of the Birds of N.Z. 2nd edition 1:30 - Type genus Turnagra Lesson, 1837
Turnagra tanagra (Schlegel, 1866) North Island Piopio
Turnagra capensis capensis (Sparrman, 1787) South Island Piopio
Turnagra capensis minor (J H Fleming, 1915) Stephens Island Piopio
Birds from the Stephens Island population are distinctive in their plumage and small size, and were thus recognised as a separate subspecies in Gill (2010) following Medway (2004).