While the present genus does indeed belong to the Gallirallus group in tribe Rallini of subfamily Rallinae, it stands apart from the numerous more basal lineages therein, and constitutes a well-distinct clade of smallish to mid-sized species distributed from Sahul far into the Pacific – across a range of at least 9,000 by 8,000 km (almost 6,000 by 5,000 miles).

Like their larger more ancestral relatives, they readily evolve into flightless island endemics in the absence of terrestrial predators; however, their smaller bulk makes it easier for them to get airborne, and more prone to be swept away by strong winds.

It has been suggested to be an aberrant individual of H. philippensis which it certainly resembles much in size, shape, and some plumage details; unpublished DNA data also indicates it belongs to this species.

Even so, the Chatham rail is very closely related to the Hypotaenidia clade, and analyses are hampered by the lack of data from the extinct and little-known species.

[2][3][6][7] Also, many Pacific rails died out before they could be studied alive by scientists, and are not even attested by skin specimens, but only from fragmentary evidence such as subfossil bones or brief reports in travellers' accounts.