Metrosideros bartlettii, commonly known as Bartlett's rÃÂtÃÂ, 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 rÃÂtÃÂ reaches a height of up to with a trunk of 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 rÃÂtÃÂ 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 rÃÂtÃÂ's range covers the northern tip of the Aupà Âuri Peninsula, in three dense forest remnants near Piwhane / Spirits Bay. Bartlett's rÃÂtàtypically 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 rÃÂtÃÂ's conservation status was assessed by the IUCN Red List in 2013 as critically endangered, and its population trend was assessed as decreasing.
Metrosideros bartlettii (Bartlett's rÃÂtÃÂ) is a tree in the family Myrtaceae, reaching a height of up to with a trunk up to 1âÂÂ1.5 m in diameter. Its bark is described as "papery" and is pale grey to whitish in colour, shedding freely, and separating into soft flakes. Its young twigs are often coloured dark red.
The leaves are (paper-like) to (leather-like) in character with laminae (leaf blades) that are 30âÂÂ50 mm long à15âÂÂ23 mm wide. Young leaves are palish-green to yellow-green and become dark green as they mature. The leaves' upper surfaces are shiny, and their lower surfaces are glossy. There are 3âÂÂ4 pairs of (very small flowers) on an inflorescence (flower cluster) with densely spreading white hairs.
Compared to other species in the genus Metrosideros, the flowering of Bartlett's rÃÂtàis unpredictable, making it unlikely that its small population can regenerate naturally. Bartlett's rÃÂtàtypically flowers in spring, from October to November; the species produces distinct white-coloured flowers with pedicels up to 3 à1 mm and a hypanthium of up to 2.5âÂÂ3 mm high à2âÂÂ2.5 mm wide. Its spreading sepals are triangle-shaped and are 1âÂÂ1.5 à1âÂÂ1.5 mm long, and its petals are to egg-shaped and are 2.5âÂÂ3 à1.8âÂÂ2 mm long. Its peduncles are 9 à1 mm long. Its stamens are 5âÂÂ9 mm long, and the styles are slightly longer at 10âÂÂ11 mm long. Its petioles are 4âÂÂ5 à1 mm long.
From March to April, Bartlett's rÃÂtàproduces small hypanthium fruits about 2.0âÂÂ2.5 mm high à2.5âÂÂ3.0 mm wide, with persistent, (bent downwards) sepals and 1.5âÂÂ2.5 mm long capsules. The pale orange-yellow seeds Bartlett's rÃÂtàproduces are 2.3âÂÂ3.0 mm long, narrowly elliptic to narrowly oval-shaped, and are straight or slightly curved.
The leaves of Bartlett's rÃÂtÃÂ have a size similar to northern rÃÂtÃÂ (M. robusta) and southern rÃÂtÃÂ (M. umbellata). The flowers of Bartlett's rÃÂtÃÂ are distinguished from those of northern rÃÂtÃÂ by their pure white colour and smaller size. Bartlett's rÃÂtÃÂ is also the only New Zealand species in the genus Metrosideros with such easily detachable and paper-like bark. Bartlett's rÃÂtÃÂ has a diploid chromosome count of 22.
Metrosideros bartlettii is categorised in the subgenus Metrosideros within the genus Metrosideros, which consists of about 58 described species across Africa, Asia, Oceania and South America. The genus consists of two main subgenera: Metrosideros (trees) and Mearnsia (vines and shrubs). There are twelve known species of Metrosideros in New Zealand; the subgenus Metrosideros comprises five tree species, M. bartlettii, M. excelsa, M. kermadecensis, M. robusta, and M. umbellata; the other superseded subgenus, Mearnsia, comprises six vine species and one shrub, M. albiflora, M. carminea, M. colensoi, M. diffusa, M. fulgens, M. perforata, and M. parkinsonii.
In 2021, a cladistic analysis from Austral Ecology of the genus Metrosideros, indicated a dispersal and radiation of the Metrosideros subgenus from New Zealand to Polynesia, Lord Howe Island and the Kermadec Islands. Their analysis, using rDNA sequencing, suggested the phylogenetic relationships within this subclade suggested a separate dispersal route into East Polynesia, including "an apparent step" from the Marquesas Islands to Hawaii. Metrosideros bartlettii and its related species are categorised in the clade (group) "Va". This clade includes two of its closest New Zealand relatives, M. excelsa and M. robusta, as well as various species from East Polynesia (including Hawaii), Lord Howe Island and the Kermadec Islands.
Bartlett's rÃÂtÃÂ was accidentally discovered in 1975 by the New Zealand botanist and schoolteacher John Bartlett while searching for liverworts near Cape Reinga. He came across the species growing at the base of a large tree in Radar Bush, near Cape Reinga. Bartlett realised it was a new species of rÃÂtÃÂ but was unable to reach any of the branches, so he instead took fragments of the bark to botanist John Dawson of the Victoria University of Wellington. Dawson thought the find was northern rÃÂtÃÂ, but Bartlett believed it was a new species, so he later returned to the area where he found the species and was able to collect a branch by shooting one off with his rifle. He then took the branch back to Wellington.
Dawson described the new species in a 1985 article in the New Zealand Journal of Botany, noting it had a "distinct whitish, spongy bark and small white flowers" and when flowers of Bartlett's rÃÂtÃÂ were first collected in 1984, it was clear to him that "a new species was involved". The examined type material for the article was collected in July 1978 by John Bartlett in Radar Bush and the isotype was collected in November 1984 by Nigel Culnie near Spirits Bay Road.
The etymology (word origin) of Bartlett's rÃÂtÃÂ's genus Metrosideros translates to English from Greek as 'iron-heart': the word means 'core' or 'heart', and means 'iron', alluding to the timber's iron-like strength. The specific epithet (second part of the scientific name), bartlettii, is named after the species' discoverer, John Bartlett. The species is commonly known as 'Bartlett's rÃÂtÃÂ' and 'rÃÂtàMoehau'; a name originating from the MÃÂori language. Bartlett's rÃÂtÃÂ's MÃÂori name was given by NgÃÂti Kurë elders in 1975 in honour of Moehau, an important ancestor for the NgÃÂti Kurë iwi (tribe).
The flowers of Bartlett's rÃÂtÃÂ are observed to be frequently visited by birds and insects (such as bees and flies), which may help spread pollen to Bartlett's rÃÂtÃÂ from other nearby Metrosideros individuals. Despite this, it is unclear what the primary pollinators of Bartlett's rÃÂtÃÂ are. Introduced species are known to visit Metrosideros in a manner similar to native species. This could be due to the inherent vulnerability of biotas on isolated oceanic islands to disruption by introduced species.
In 2018, two New Zealand botanists, Carlos Lehnebach and Karin van der Walt, examined the pollination and the flower development of Bartlett's rÃÂtÃÂ. In their study, published in the New Zealand Plant Conservation Network, they found that Bartlett's rÃÂtàis a self-incompatible tree, meaning that its flowers will only seed if it is pollinated by pollen from a genetically distinct tree. In 2021, the New Zealand Journal of Botany published a similar study in which researchers and scientists analysed the ex situ conservation of Bartlett's rÃÂtàindividuals at à Âtari-Wilton's Bush. Their analyses confirmed the self-incompatibility of Bartlett's rÃÂtÃÂ, which is consistent with other species within the genus Metrosideros. Although it was speculated that self-incompatibility occurred in Bartlett's rÃÂtÃÂ, it had never been experimentally confirmed until these two studies. In their 2021 analyses, hand-pollination of Bartlett's rÃÂtàindividuals produced seeds with generally low germination rates; this biological finding is consistent with other species in the family Myrtaceae, such as pà Âhutukawa and mÃÂnuka (Leptospermum scoparium). Their analyses also confirmed that hybridisation between Bartlett's rÃÂtàand pà Âhutukawa resulted in capsule formations; however, the seeds from their analyses had "very low" viability.
A 2022 research article on the cross-pollination of cultivated Bartlett's rÃÂtÃÂ individuals, published in the Pacific Conservation Biology, revealed that cross-pollination is the only viable method that produces seeds that can be used in naturalised populations. The research article also revealed that the flower development of Bartlett's rÃÂtÃÂ is characterised by dichogamy, which is a method to prevent self-pollination by having stigma receptivity and release of pollen occur sequentially, i.e., not at the same time. Their study found that Bartlett's rÃÂtÃÂ's breeding strategy favours cross-pollination and has very little inbreeding.
The endemic liverwort species Frullania wairua and Siphonolejeunea raharahanehemiae, both at risk of extinction, are known to be hosted by Bartlett's rÃÂtÃÂ. Anthracophyllum archeri, a species of fungus in the family Omphalotaceae and other fungi in the genus Cladobotryum, were also observed to be growing on the bark and the fallen twigs of Bartlett's rÃÂtÃÂ in native forest in Te Paki, Northland.
Bartlett's rÃÂtàis endemic to the Northland Region in New Zealand's North Island. Its range covers the northern tip of the Aupà Âuri Peninsula, in three patches of dense forest remnants near Piwhane / Spirits Bay, these being: Kohuronaki Bush, Radar Bush, and Unuwhao Bush. At the time of the original species description in 1985, only seven naturalised adult individuals were known to be located at two of the sites. Later in the mid-1990s, New Zealand's Department of Conservation recorded nineteen adult individuals. Then, a 2000 research article of Bartlett's rÃÂtÃÂ, published in Molecular Ecology, revealed an additional twelve adult individuals, bringing the known species count of Bartlett's rÃÂtàto thirty-one in the year 2000.
Before a DNA profiling test of Bartlett's rÃÂtàindividuals was conducted in 2015, the Department of Conservation was unaware that three of the five genotypes required to grow genetically suitable trees were located within the tribal territories of the NgÃÂti Kurë and Te Aupà Âuri iwi. At most, five of the fourteen trees in 2015 possessed the unique genotypes required for the genetic diversity, which is essential to the species' existence. New Zealand botanist and science advisor Peter de Lange stated that without intervention "the future was bleak" for Bartlett's rÃÂtÃÂ. The 2018 article by Lehnebach and Van der Walt, published by the New Zealand Plant Conservation Network, has since reported only thirteen adult trees in the wild.
Bartlett's rÃÂtàis usually found growing near bodies of water, such as streams and swamps. Bartlett's rÃÂtÃÂ's habitat favours dense lowland forests; the plant usually germinates and begins life as an epiphyte (growing on another plant), specimens have been observed growing on: pà «riri (Vitex lucens), rewarewa (Knightia excelsa), taraire (Beilschmiedia tarairi), and tree ferns (Cyathea). Bartlett's rÃÂtàhave occasionally been observed growing on boulders, cliff sides, and rock outcrops.
Bartlett's rÃÂtÃÂ is one of New Zealand's most threatened and rarest trees. Its conservation status was assessed by the IUCN Red List in 2013 as critically endangered, and its population trend was evaluated as decreasing. Its assessment in the New Zealand Threat Classification System was evaluated in 2023 as nationally critical. The decline of Bartlett's rÃÂtÃÂ is attributed to land use changes following human settlement and the introduction of common brushtail possums, an invasive species in New Zealand, which browse its buds, flowers, and shoots. Another threat to Bartlett's rÃÂtÃÂ is myrtle rust, a type of plant disease that infects many species in the family Myrtaceae, including Bartlett's rÃÂtÃÂ. Although Bartlett's rÃÂtÃÂ is uncommon in the wild, it is common in and is found in several private and botanic gardens across the country.
The habitat disturbance of Bartlett's rÃÂtàbegan with the arrival of the first human settlers from East Polynesia in 1250 â 1300 CE. Later in the 1800s, New Zealand experienced the arrival of European settlers, who cleared many forests, contributing to the habitat disturbance of Bartlett's rÃÂtÃÂ. Although the forests in Northland are gradually recovering, the population of Bartlett's rÃÂtàremains low and is scattered between three known locations near Piwhane / Spirits Bay.
Unless immediate conservation measures are taken, Bartlett's rÃÂtàhas a high chance of becoming extinct due to its ongoing decline, small population size, and reproductive failure. In 2020, the NgÃÂti Kurë iwi established a planting programme in collaboration with Manaaki Whenua â Landcare Research with the aim of increasing and protecting the number of Bartlett's rÃÂtàtrees remaining in the wild. , there has been over five hundred new plantings of Bartlett's rÃÂtàin Cape Reinga. The programme aims to increase the number of individuals to four thousand.
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