Metrosideros bartlettii, commonly known as Bartlett's rātā, is a rare species of tree in the family Myrtaceae. It is endemic to the Northland Region in New Zealand's North Island. Bartlett's rātā reaches a height of up to 30 metres (100 feet) with a trunk of 1–1.5 metres (3 ft 3 in – 4 ft 11 in) in diameter. The species is classified in the subgenus Metrosideros and is known for its distinct whitish, paper-like bark and small white-coloured flowers. Bartlett's rātā was first discovered in 1975 by the New Zealand botanist and schoolteacher John Bartlett, who accidentally discovered the species while searching for liverworts near Cape Reinga. It was first described by botanist John Dawson in a 1985 article in the New Zealand Journal of Botany.

Bartlett's rātā's range covers the northern tip of the Aupōuri Peninsula, in three dense forest remnants near Piwhane / Spirits Bay. Bartlett's rātā typically begins life as an epiphyte (growing on another plant); it inhabits lowland forests and is usually found growing near wet areas. A 2018 article by the New Zealand Plant Conservation Network documented 13 adult trees in the wild, a significant decrease from another research article in 2000 that documented 31 wild adult trees. The species has a high chance of becoming extinct in the wild unless immediate conservation measures are taken to stop its ongoing decline, which has been attributed to land use changes following human settlement and the introduction of common brushtail possums, which browse its buds, flowers, and shoots. Bartlett's rātā's conservation status was assessed by the IUCN Red List in 2013 as critically endangered, and its population trend was assessed as decreasing.

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