''Metrosideros robusta'', the northern rātā, is a forest tree endemic to

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...

. It grows up to or taller, and usually begins its life as a

hemiepiphyte A hemiepiphyte is a plant that spends part of its life cycle as an epiphyte. The seeds of primary hemiepiphytes germinate in the canopy and initially live epiphytically. They send roots downward, and these roots eventually make contact with t ...

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 rātā will grow on the ground with a normal but short trunk.

Distribution

Northern rātā is found in the

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from Te Paki in the north to

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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

Hawkes Bay Hawke's Bay ( mi, Te Matau-a-Māui) is a local government region on the east coast of New Zealand's North Island. The region's name derives from Hawke Bay, which was named by Captain James Cook in honour of Admiral Edward Hawke. The region i ...

. In the

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasma ...

, northern rātā is common from

Nelson Nelson may refer to: Arts and entertainment * ''Nelson'' (1918 film), a historical film directed by Maurice Elvey * ''Nelson'' (1926 film), a historical film directed by Walter Summers * ''Nelson'' (opera), an opera by Lennox Berkeley to a lib ...

Greymouth Greymouth () ( Māori: ''Māwhera'') is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coas ...

and

Hokitika Hokitika is a town in the West Coast region of New Zealand's South Island, south of Greymouth, and close to the mouth of the Hokitika River. It is the seat and largest town in the Westland District. The town's estimated population is as of ...

. It reaches its southern limit near Lake Mahinapua at 42°4′ South latitude. The natural habitat is forest along the coasts and in the lowlands. In some parts of its range northern rātā occurs in montane forest. Formerly, with rimu (''

Dacrydium cupressinum ''Dacrydium cupressinum'', commonly known as rimu, is a large evergreen coniferous tree endemic to the forests of New Zealand. It is a member of the southern conifer group, the podocarps. The Māori name ''rimu'' comes from the Polynesian ...

'') it was a dominant tree in a forest type known as rimu/rātā forest.

Description

Northern rātā is a massive tree, easily distinguished from other ''Metrosideros'' species by its small, leathery, dark green leaves that are 25–50mm long by 15–25mm wide, 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 (''Freycinetia banksii'') is a densely branched, brittle, woody climber native to New Zealand. It is a member of the screwpalm family Pandanaceae. Kiekie has numerous cane-like stems up to 40 mm in diameter, which freely produce aer ...

'' (kiekie). The wood is reddish brown, and the manner of its growth results in a twisted grain.

Hemi-epiphytic growth habit

Northern rātā often 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 rātā is usually rimu. In former times, the tree was described as a 'strangler', however it may be that rātā can only establish in trees that are already in decline. Northern rātā usually occurs in hardwood, podocarp, and

southern beech ''Nothofagus'', also known as the southern beeches, is a genus of 43 species of trees and shrubs native to the Southern Hemisphere in southern South America (Chile, Argentina) and Australasia (east and southeast Australia, New Zealand, New Gu ...

forests. It is often associated with such species as rewarewa, tawa, hīnau,

kānuka ''Kunzea ericoides'', commonly known as kānuka, kanuka, white tea-tree or burgan, is a tree or shrub in the myrtle family, Myrtaceae and is endemic to New Zealand. It has white or pink flowers similar to those of ''Leptospermum'' and from i ...

, kahikatea, kāmahi,

kohekohe Kohekohe ('' Dysoxylum spectabile'') is a medium-sized tree in the Meliaceae family, native to New Zealand. It is found in lowland and coastal forests throughout most of the North Island and also occurs in the Marlborough Sounds in the nort ...

pukatea ''Laurelia novae-zelandiae'', also called pukatea, is a large evergreen tree, endemic to the forests of New Zealand. Pukatea has 'toothed' leaves and produces small flowers. It is a species in the Atherospermataceae (formerly Monimiaceae) f ...

and māhoe.

Conservation

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

pōhutukawa ''Metrosideros excelsa'', commonly known as pōhutukawa ( mi, pōhutukawa), New Zealand Christmas tree, New Zealand Christmas bush, and iron tree, is a coastal evergreen tree in the myrtle family, Myrtaceae, that produces a brilliant display o ...

is another threat to the survival of northern rātā. Pōhutukawa has naturalised in areas south of its natural range, and poses a problem in localities where the northern or southern rātā species are present. Other threats include cutting for firewood, and forest clearance for roading or construction.

Cultivation

Northern rātā 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

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...

s of northern rātā have been released. There are also known cultivars of hybrids between northern rātā and pōhutukawa (known as ''Metrosideros ×sub-tomentosa''), and between northern rātā and southern rātā. Known cultivars include: ∞ Hybrid of northern rātā and southern rātā
¤ Hybrid of northern rātā and pōhutukawa

References