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Metrosideros bartlettii

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Bartlett's rātā
A New Zealand forest with Bartlett's rātā in the centre.
M. bartlettii observed by botanist Peter de Lange in 2011
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Myrtales
Family: Myrtaceae
Genus: Metrosideros
Species:
M. bartlettii
Binomial name
Metrosideros bartlettii

Metrosideros bartlettii, commonly known as the Bartlett's rātā, is a tree endemic to only a few parts of the Northland Region in New Zealand's North Island. It is one of twelve Metrosideros species in the family Myrtaceae. The Bartlett's rātā was first discovered in 1975 by New Zealand botanist and schoolteacher, John Bartlett. There are three known patches of dense native forest near Piwhane / Spirits Bay that contain Bartlett's rātā: Radar Bush, Kohuronaki Bush, and Unuwhao Bush. Bartlett's rātā has a high chance of becoming extinct unless immediate conservation measures are taken, due to its ongoing decline. As of 2018, only 13 adult trees are known to exist in the wild. Bartlett's rātā is common in cultivation, with it being found in several private and botanic gardens throughout New Zealand. Its current conservation status was assessed by the International Union for Conservation of Nature (IUCN) Red List as "Critically Endangered" and its population trend was assessed as "Decreasing".

Description

Bright green leafage of Bartlett's rātā, in Ōtari-Wilton's Bush
Foliage of Bartlett's rātā (M. bartlettii) in Ōtari-Wilton's Bush

Metrosideros bartlettii (Bartlett's rātā) is a rare tree endemic to the Northland Region of the North Island of New Zealand. It grows to a height of up to 25 m (82 ft) with a trunk up to 1 m (3 ft 3 in) in diameter, its twigs are often coloured dark red. Its bark is pale grey to whitish in colour. Its leaves are chartaceous to coriaceous in character, glossy, palish-green in colour and its lamina, being 30–50 × 15–26 mm long. There are 3–4 pairs of cymules (very small flowers) on an inflorescence (flower spike) with densely spreading white hairs.[2]

Compared to other species in the Metrosideros genus, flowering of the Barlett's rātā is unpredictable, making it unlikely the small wild population can regenerate without human assistance. Flowering generally occurs from October to November it produces white coloured pedicels of up to 3 x 1 , 2.5–3 mm high, 2–2.5 mm wide, and spreading 1–1.5 x 1–1.5 mm.[2][3][4] Fruiting occurs from March to April, producing a hypanthium fruit being 2.0–2.5 × 2.5–3.0 mm long, with persistent, deflexed sepals and 1.5–2.5 mm-long capsules. The pale orange-yellow seeds are 2.3–3.0 mm long and narrowly elliptic to narrowly oval shaped.[5]

Taxonomy

It was first discovered in 1975 by New Zealander John Bartlett, a schoolteacher and botanist from Hamilton.[6] Bartlet discovered the tree in Radar Bush, 9.5 km (5.9 mi) south east from Cape Reinga.[7][3] It was discovered by Bartlett was searching for liverworts in the Northland Region of New Zealand, untill he found a specimen growing at the base of a large tree. Bartlett realised it was a new species of rātā, but was unable to reach any branches so he instead took fragments of the bark to the Victoria University of Wellington and to botanist John Dawson, who incorrectly thought the find was northern rātā (M. robusta). Bartlett later returned to the area and was able collect a branch and later took it to Wellington.[8] Bartlett's rātā is closely related to northern rātā;[5] its leaves are of similar size and share characteristics to southern rātā (M. umbelata) and northen rātā. Bartlett's rātā's flowers are significantly smaller than those of northern rātā. M. oreomyrtus, endemic to New Caledonia, is the only other tree in the genus Metrosideros with white-coloured flowers.[9]

Etymology

The etymology of Bartlett's rātā's genus, Metrosideros, translates to English to 'iron heart'. Metrosideros derives from the Greek language; the word metra means 'core' or 'heart', and sideron means 'iron'.[5][10] The scientifical name, bartlettii, is the Latinisation after the tree's discoverer John Bartlett.[2] Bartlett's rātā is also commonly known as rātā moehau.[5]

  • An image of Bartlett's rātā's white-coloured flowers
    Close up of Bartlett's rātā's white-coloured flowers
  • The "flakey" grey to whitish bark of Bartlett's rātā
    "Flakey" bark of Bartlett's rātā
  • Recently formed buds of Bartlett's rātā
    Recently formed buds of the tree

Ecology

Bartlett's ratā is often observered to be utilised by birds and insects (such as bees and flies), which may help spread pollen from other Metrosideros species.[11] New Zealand species of Metrosideros are pollinated by nectar-feeding birds, such as the tūī (Prosthemadera novaeseelandiae) which are known to forage over distances of 15 km (9.3 mi).[12] Wind and rain may cause self-pollination but the likelihood of producing viable seeds is low or nonexistent. A 2022 study by the Pacific Conservation Biology revealed cross-pollination is the only method that produces viable Barlett's rātā seeds that can be utilised in other augmented wild populations.[11][13]

A 2021 study by the New Zealand Journal of Botany conducted scintifical analyses of Bartlett's rātā at Ōtari-Wilton's Bush (in Wellington) which confirmed the self-incompatibility of Bartlett's rātā individuals depend on pollen from unrelated individuals to set its fruit. Recent and historical genetical research has confirmed hybridisation and introgression are possible between closely related species in the Metrosideros genus. The average germination of the seeds from Bartlett's rātā's controlled pollination, was usually low, which is consistent with other species in the family Myrtaceae, such as pōhutukawa (Metrosideros excelsa) and mānuka (Leptospermum scoparium).[14]

Distribution

Bartlett's rātā is endemic to New Zealand's North Island to the Northland Region. It is only known to be located in Te Paki, in three patches of forest remnants near Piwhane / Spirits Bay. These being; Kohuronaki Bush, Radar Bush, and Unuwhao Bush.[5][12] It is usually found growing near bodies of water (such as streams) and in swamplands.[15] An article from Molecular Ecology, published in 2000, documented 31 adult trees.[7] A 2018 study by the New Zealand Journal of Botany has since documented only 13 adult trees,[16] and most of these trees are located on private land.[17] Bartlett's rātā was likely never a common tree. A number of surveys were conducted in the 1990s which revealed individuals were only present in three populations.[18] Bartlett's rātā was likely restricted to New Zealand's far north during the Pleistocene era, and it remained there throughout the Holocene era's warming.[11]

Conservation

An image of a common bush tail possum. Bartlett's rātā's decline is largely due to their introduction into New Zealand.
Bartlett's rātā historical decline is largely due to land use changes following settlement, and the introduction of bushtail possums.

Its current conservation status was assessed by the IUCN Red List in 2013 as "Critically Endangered" and its population trend was assessed as "Decreasing".[1] The historical decline of Bartlett's rātā is largely due to land use changes following settlement, and the introduction of brushtail possums (an invasive species in New Zealand).[13][19] Although Bartlett's rātā is uncommon in the wild, it is common in cultivation, with it being found in several private and botanic gardens throughout the country (such as Ōtari-Wilton's Bush).[16]

Bartlett's rātā habitat disturbance began with the arrival of the Polynesian settlers. Many forests were later cleared when the European (Pākehā) settlers arrived later, starting in the early 1800s. Its habitat retreated into the steeper valleys, especially those under intense fire shadows. It was not until the late 1960s that the far north's native forest area began to decline. Although the forests in Northland are gradually recovering, the population of Bartlett's rātā remains low and widely scattered.[12]

Bartlett's rātā has a high chance of becoming extinct, unless immediate conservation measures are taken, due to its ongoing decline, population size, and reproductive failure. Bartlett's rātā breeding strategy favours cross-pollination, and has little inbreeding. Bartlett's rātā under cultivation has low levels of genetic variety, which might restrict its ability to contribute to the its overall conservation.[20]

See also

References

Citations

  1. ^ a b De Lange 2014.
  2. ^ a b c Dawson 1985, p. 1.
  3. ^ a b Bercusson & Torrence 1998, p. 67.
  4. ^ Nadarajan et al. 2021, p. 3.
  5. ^ a b c d e De Lange 2024.
  6. ^ Galloway & Edgar 1987, p. 2.
  7. ^ a b Drummond et al. 2000, p. 1.
  8. ^ Judd 2000.
  9. ^ Dawson 1985, p. 3.
  10. ^ Bylsma, Clarkson & Efford 2014, p. 4.
  11. ^ a b c Nadarajan et al. 2021, p. 8.
  12. ^ a b c Drummond et al. 2000, p. 8.
  13. ^ a b Van der Walt, Alderton-Moss & Lehnebach 2022, p. 2.
  14. ^ Nadarajan et al. 2021, p. 14.
  15. ^ Dawson 1985, p. 2.
  16. ^ a b Nadarajan et al. 2021, pp. 2–3.
  17. ^ Stowell 2017.
  18. ^ Nadarajan et al. 2021, p. 1.
  19. ^ Pattabiraman et al. 2022, p. 3.
  20. ^ Van der Walt, Alderton-Moss & Lehnebach 2022, p. 9.

Works cited

Journals

Miscellaneous

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