Metrosideros robusta, commonly known as the northern rÃÂtÃÂ, is a forest tree endemic to New Zealand. It grows up to or taller, and usually begins its life as a hemiepiphyte high in the branches of a mature forest tree; over centuries the young tree sends descending and girdling roots down and around the trunk of its host, eventually forming a massive, frequently hollow pseudotrunk composed of fused roots. In disturbed ground, or where there are gaps in the forest cover, northern rÃÂtÃÂ will grow on the ground with a normal but short trunk.
Northern rÃÂtàis found in the North Island from Te Paki in the north to Wellington in the south. Formerly widespread, it is now uncommon over large parts of its former range, and is apparently absent from all but the south-east of Hawke's Bay. In the South Island, northern rÃÂtàis common from Nelson to Greymouth and Hokitika. It reaches its southern limit near Lake Mahinapua at 42ð4â² South latitude. The natural habitat is forest along the coasts and in the lowlands. In some parts of its range northern rÃÂtàoccurs in montane forest. Formerly, with rimu (Dacrydium cupressinum) it was a dominant tree in a forest type known as rimu/rÃÂtàforest.
In 2024 an unusual 105 feet (32 meters) tall northern rÃÂtÃÂ near Karamea on the west coast of South Island, nicknamed the "walking tree" because of its pair of leg-like trunks resembling legs walking across a field, won the New Zealand Arboricultural Association's (NZ Arb)'s Tree of the Year Award with 42% of the public vote.
Northern rÃÂtÃÂ is a massive tree, easily distinguished from other Metrosideros species by its small, leathery, dark green leaves that are long, and have a distinct notch at the tip. Young growth is generally pink and covered in fine rust-coloured hairs that are gradually shed as the foliage ages but tend to persist at the midrib and in the vicinity of the leaf base. The flowers, borne in sprays on the tips of branches, are a mass of dark scarlet stamens. Flowering peaks between November and January, and seeds take a year or slightly more to ripen. The bark is usually brown or grey-brown and rather corky and provides an ideal stratum for the roots of epiphytic plants such as Astelia species and Freycinetia banksii (kiekie). The wood is reddish brown, and the manner of its growth results in a twisted grain.
Northern rÃÂtàoften begins life as hemi-epiphyte, and the resultant tree has a hollow trunk up to 4 m in diameter made up of interlocking roots that enclose the space left by the former host tree. The host tree of epiphytic northern rÃÂtàis usually rimu. In former times, the tree was described as a 'strangler', however it may be that rÃÂtàcan only establish in trees that are already in decline. Northern rÃÂtàusually occurs in hardwood, podocarp, and southern beech forests. It is often associated with such species as rewarewa, tawa, hënau, kÃÂnuka, kahikatea, kÃÂmahi, kohekohe, pukatea and mÃÂhoe.
The greatest threat to northern rata is browsing by introduced possums (Trichosurus vulpecula), which cause severe damage by eating the leaves, buds, flowers and young shoots of the tree. In severe cases this can lead to the death of the tree within two years. In some districts, this has resulted in the local loss of the species. The situation of the species has been improved through the efforts of Project Crimson. Hybridisation with pà Âhutukawa is another threat to the survival of northern rÃÂtÃÂ. Pà Âhutukawa has naturalised in areas south of its natural range, and poses a problem in localities where the northern or southern rÃÂtàspecies are present. Other threats include cutting for firewood, and forest clearance for roading or construction.
Northern rÃÂtÃÂ may be propagated readily from fresh seed. Viability of the seed drops quickly after a few weeks or if it is allowed to dry out. Cuttings do not strike readily, but better results can be obtained from using water shoots.
At least three cultivars of northern rÃÂtàhave been released. There are also known cultivars of hybrids between northern rÃÂtàand pà Âhutukawa (known as Metrosideros ÃÂsub-tomentosa), and between northern rÃÂtàand southern rÃÂtÃÂ. Known cultivars include:
â Hybrid of northern rÃÂtàand southern rÃÂtÃÂ<br> ä Hybrid of northern rÃÂtàand pà Âhutukawa