Urtica ferox

Urtica ferox
A small plant with green leaves. Each leaf has a row of white, sharp looking stinging hairs (trichomes) running up the middle of it. The leaves also have jagged edges.
Leaves and trichomes of U. ferox
Not Threatened
Not Threatened (NZ TCS)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Embryophytes
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Rosales
Family: Urticaceae
Genus: Urtica
Species:
U. ferox
Binomial name
Urtica ferox

Urtica ferox, commonly known as tree nettle and ongaonga, is a species of nettle endemic to New Zealand. A member of the Urticaceae, the plant is covered in trichomes (stinging hairs), which contain numerous toxins that are poisonous to humans. It is a large woody shrub or small tree that can grow to a height of 3 metres (10 feet). Its trichomes can cause painful stings that can last several days or weeks; the sting is strong enough to kill cattle, dogs, and horses. There are two recorded human deaths from contact with the plant.

The plant was first scientifically described by German naturalist Georg Forster in 1786. U. ferox is wind-pollinated, and its seeds are later dispersed by gravity or the wind. The plant serves as a host for several butterfly and moth species, and it is the primary source of food for the larvae of the New Zealand red admiral (Vanessa gonerilla) butterfly. Despite being a plant usually avoided by people, U. ferox has some traditional and medicinal uses for the indigenous Māori people. Its 2023 assessment in the New Zealand Threat Classification System was "Not Threatened".

Description

Close-up photo of U. ferox stinging hairs (trichomes) running up the middle of the leaf
Trichomes along the leaf mid-vein
Close-up photo of buds and developing flowers, a stem with many stinging hairs (trichomes) is on the right side of the image
Buds and developing flowers

Urtica ferox (ongaonga) is a dioecious (either male or female) shrub or small tree in the nettle family Urticaceae. It can grow to a height of 3 metres (10 feet) with the base of the stem or trunk reaching 12 cm (5 in) in thickness.[1][2] The pale green leaves are thin and membranous, and the surface of the leaves, stems, and stalks are covered in stiff trichomes (stinging hairs) that can grow up to 6 mm (0.24 in) long. These trichomes are prominent along the salient mid-vein and leaf margin. The leaves range from 3–5 cm (1.2–2.0 in) in width and 8–12 cm (3.1–4.7 in) in length. They are arranged in opposite pairs.[3][4][5] Juvenile leaves can reach up to 15 cm (5.9 in) long.[4] The leaf shape is triangular, ovate-triangular, to lanceolate-triangular with coarsely serrated leaf margins.[3][4][6]

Flowering occurs from November to March.[1] The flowers are produced in panicles (branched flower clusters), which can reach 8 cm (3.1 in) long.[6][2] Pollen grains are collected by the densely packed stigmas on the flowers.[7][8] Fruiting occurs from December to May; the fruits are found in achenes (dry one-seeded fruits), each containing a single seed, which is 1.5 mm (0.059 in) long. These seeds take about one month to germinate.[7][1][8] Burrows (1996) found that U. ferox is capable of building up large seed banks (dormant soil seeds) in the soil which may survive for several years, like European species in the genus Urtica which also show seed bank dormancy.[9] U. ferox has a diploid chromosome count of 48.[1]

Taxonomy

Urtica ferox was first scientifically described by German naturalist Georg Forster in 1786.[10][11] The plant was collected during the second voyage of James Cook.[12] As of 2026, there are 69 species of the Urtica genus accepted by the Plants of the World Online taxonomic database, which are found throughout the world.[13] Among the six species of Urtica native to New Zealand,[14] U. ferox is unique owing to it being tall and woody.[15][16] Grosse‐Veldmann et al. (2016) constructed a phylogenetic tree of the genus Urtica based on gender characteristics and genetic sequencing.[17] The tree showed that U. ferox is not closely related to the other native species and is instead the sister species to the South African U. lobulata.[18][15] It has been presumed that the distinctive morphological evolution and toxicity of U. ferox is a result of the ecological influence of browsing by the now-extinct moa – giant, flightless birds.[15][19]

Etymology

The etymology of the genus name Urtica is derived from the Latin word for stinging nettles, which comes from urere, meaning 'to burn'. The specific epithet ferox means 'ferocious', 'savage', or 'wild'.[20][21] U. ferox is commonly known as tree nettle and ongaonga.[1][22] In Māori, the word ongaonga is used to describe anything 'annoying' or 'irritating'. Cognates (related words) found across different Polynesian languages, including 'hongohongo' and 'okaoka', are words typically used to describe stinging insects.[20] U. ferox has several recorded Māori names, including houhi, ongaonga, okaoka, puruhi, taraonga, and taraongaonga.[23][24]

Ecology

Clusters of pale, pinkish gall fluffy structures caused by Vittacus mansoni on the surface of a green leaf
Vittacus mansoni, a species of gall mite that induces galls on U. ferox.
A female New Zealand red admiral butterfly, a butterfly with black and brown coloured wings with red and white markings, visiting the leaves of U. ferox
A female New Zealand red admiral (Vanessa gonerilla) laying eggs on U. ferox.

Urtica ferox seeds are dispersed by gravity and the wind.[25] Like all Urtica species, U. ferox is wind-pollinated,[26][27] although bees may visit the flowers to collect nectar.[5][28] During winter in some southern localities, U. ferox can be semideciduous (losing some of its leaves) or entirely deciduous (losing all of its leaves). This characteristic is uncommon in New Zealand's native plants, only being found in about 5% of the country's native woody species.[29][30][31]

The plant is the primary host for the larvae of the endemic mainland New Zealand red admiral (Vanessa gonerilla subsp. gonerilla),[32][33] which begin laying eggs in early spring (September).[34][33] The butterflies lay their eggs on the new growth of U. ferox leaves, typically at the tip and often on the side with the trichomes.[35] After hatching, the caterpillar larvae then spend up to six weeks feeding on those leaves. During this vulnerable stage, the caterpillars use the spiny leaves for protection, wrapping the leaves around themselves like a blanket or building a small tent to hide from potential predators such as birds and insects. Populations of V. gonerilla have had a perceived decline, possibly in part because of people treating U. ferox as a weed and removing it.[34]

Several moth species feed on the plant as larvae, including Mnesictena flavidalis, Diarsia intermixta, Meterana inchoata, Pasiphila urticae, Epichorista crypsidora, two species of Pseudocoremia, and species of Udea.[5][36] A rare moth species, Pseudocoremia flava, uses U. ferox as a host plant.[37] The beetle Oemona hirta can also be found on the plant.[38] A species of gall mite, Vittacus mansoni, uses U. ferox as a host plant, and a leaf miner species of fly Liriomyza urticae.[39][40] Rust fungi of the genus Puccinia and the leaf spot Ramualria urticae can also be present on the plant.[41][42] Deer, sheep, and goats eat U. ferox's leaves in spite of the trichomes.[5][26] The fruits are also eaten by common brushtail possums.[5][43]

Toxins

U. ferox's trichomes contain the neurotransmitters histamine, serotonin, and acetylcholine.[22][44] These neurotransmitters have also been found in U. dioica and U. urens.[45] A 2022 study in the Journal of Biological Chemistry found that two peptides, Δ-Uf1a and β/δ-Uf2a, are likely responsible for the painful sensations. Δ-Uf1a is suggested to create pain by disturbing cell membranes and β/δ-Uf2a the same by modulating voltage-gated sodium channels. Stings have a painful reaction which causes hives, numbness, and itchiness. In serious cases, the stings can also cause ataxia, blurred vision, confusion, polyneuropathy, respiratory distress, and hypersalivation. These sting reactions can last for days to weeks.[22][46]

The reaction to U. ferox's sting can potentially be fatal,[6][47][22] with two recorded human deaths from contact with U. ferox. One death occurred in 1961, when a young hunter died five hours after walking through a patch of U. ferox bushes in the Ruahine Ranges.[48][1][6] In 2002, another young man's death in the Ruahine Ranges was retrospectively attributed to U. ferox by a pathologist.[49] In one self-experimenting account, the sting of U. ferox was described as producing an immediate burning sensation at the point of contact, with the pain subsiding after five minutes and being absent after 60 minutes.[50] The plant has killed cattle, dogs, and horses in the past.[5][44][6]

Distribution

A large U. ferox bush and other green plants growing right next to a stream
A large U. ferox bush growing next to a stream near Porirua

Urtica ferox is endemic to New Zealand where it is found throughout the North and South Islands.[1] Otago was thought to be the species' southern limit by botanist Thomas Cheeseman;[51] however, a 2011 book of New Zealand flora suggests that the plant occurs as far south as Stewart Island.[52] The plant varies in abundance throughout its distribution area, being especially common near Wellington and Christchurch,[5] whilst they are uncommon or absent north of Auckland (as noted by botanist Lucy Moore in 1978).[53] The 2023 assessment of U. ferox in the New Zealand Threat Classification System was "Not Threatened",[54] but in the Northland Region, it has been assessed as "Regionally Critical" with an estimated 250 mature U. ferox plants in the region.[55]

Habitat

Urtica ferox is typically found in coastal to lowland environments.[1] It is common in forest margins and shrublands, and it occurs from sea level to 800–1,000 m (2,600–3,300 ft) above sea level.[5][48] U. ferox grows on a variety of soil types but prefers fertile, basaltic soils. It also occurs on inland basaltic formations, including in the Canterbury Region on the Harper Hills near Glentunnel. The plant can be found on alluvial soils in the Taramakau Valley of Westland District, within Arthurs Pass National Park.[26] U. ferox can also be found growing on the bases of fallen trees and streambeds.[26][56]

Uses

Urtica ferox is a plant usually avoided by people, but it did have some traditional and medicinal uses for the indigenous Māori people.[57] In rongoā (traditional medicinal practices), the bark of U. ferox and the leaves of kawakawa (Piper excelsum), boiled together, were used to treat eczema and sexually transmitted infections.[20] The plant was also a traditional Māori food source. The inner stems were consumed after the leaves and outer bark had been removed. The thin film that makes up the inner bark was also eaten raw and is said to have a sweet taste.[34][24] In Māori mythology, the plant was placed in forests to prevent people moving freely and to irritate people. The Polynesian explorer Kupe was said to have placed several obstacles, including this plant, to slow down those chasing him.[44]

References

  1. 1 2 3 4 5 6 7 8 De Lange 2026.
  2. 1 2 Salmon 1986, p. 224.
  3. 1 2 Metcalf 2009, p. 106.
  4. 1 2 3 Allan 1961, p. 403.
  5. 1 2 3 4 5 6 7 8 Crowe 2009, p. 36.
  6. 1 2 3 4 5 Connor 1977, p. 182.
  7. 1 2 Burrows 1996, pp. 1–2.
  8. 1 2 Eagle 2006, p. 416.
  9. ↑ Burrows 1996, pp. 7–8.
  10. ↑ Forster & Dietrich 1786, p. 66.
  11. ↑ IPNI 2026.
  12. ↑ Nicolson & Fosberg 2004, p. 682.
  13. ↑ POWO 2026.
  14. ↑ Grosse-Veldmann, Conn & Weigend 2016, p. 1.
  15. 1 2 3 Grosse-Veldmann et al. 2016, pp. 9–10.
  16. ↑ Grosse-Veldmann, Conn & Weigend 2016, p. 3.
  17. ↑ Grosse‐Veldmann & Weigend 2018, p. 3.
  18. ↑ Grosse‐Veldmann & Weigend 2018, p. 16.
  19. ↑ Xie et al. 2022, p. 8.
  20. 1 2 3 Vennell 2019, p. 180.
  21. ↑ Marrassini et al. 2010, p. 1.
  22. 1 2 3 4 Xie et al. 2022, p. 1.
  23. ↑ Manaaki Whenua 2021.
  24. 1 2 Best 1902, p. 60.
  25. ↑ Burrows 1994, p. 5.
  26. 1 2 3 4 Burrows 1999, p. 1.
  27. ↑ Friis 1993, p. 5.
  28. ↑ Butz Huryn 1995, pp. 10–11.
  29. ↑ Burrows 1996, p. 2.
  30. ↑ McGlone et al. 2004, pp. 1, 7.
  31. ↑ Wardle 1978, p. 2.
  32. ↑ Sanger, Lord & Jandt 2025, pp. 1–2.
  33. 1 2 Barron, Barlow & Wratten 2003, p. 2.
  34. 1 2 3 Vennell 2019, p. 181.
  35. ↑ Gibbs 1980, p. 112.
  36. ↑ Patrick 2021, p. 4.
  37. ↑ Chambers 1977, p. 1.
  38. ↑ Sopow & Bain 2017, pp. 10–12.
  39. ↑ Xue, Song & Hong 2005, p. 1.
  40. ↑ Spencer 1976, pp. 25, 57.
  41. ↑ McKenzie, Pennycook & Padamsee 2024, p. 4.
  42. ↑ Braun & Hill 2004, p. 10.
  43. ↑ Cowan 1990, p. 1.
  44. 1 2 3 Vennell 2019, p. 179.
  45. ↑ Connor 1977, p. 184.
  46. ↑ Hammond‐Tooke et al. 2007, p. 1.
  47. ↑ Kanzaki et al. 2010, p. 1.
  48. 1 2 Wassilieff 2009.
  49. ↑ The New Zealand Herald 2020.
  50. ↑ Parry & Buenz 2018, p. 1.
  51. ↑ Cheeseman 1906, p. 634.
  52. ↑ Dawson et al. 2019, p. 540.
  53. ↑ Moore 1978, p. 82.
  54. ↑ New Zealand Threat Classification System.
  55. ↑ Ford et al. 2026, pp. 19, 24.
  56. ↑ Cranwell & Moore 1935, p. 6.
  57. ↑ Vennell 2019, p. 179–181.

Works cited

Books

  • Allan, Harry Howard (1961). Flora of New Zealand. Vol. 1. P D Hasselberg Government Printer Publications. ISBN 978-0-477-01056-6 – via the Internet Archive.{{cite book}}: CS1 maint: ignored ISBN errors (link)
  • Cheeseman, Thomas Frederick (1906). Manual of the New Zealand flora (1 ed.). Wellington, New Zealand: New Zealand Board of Science and Art – via the Internet Archive.
  • Connor, Henry Eamonn (1977). The Poisonous Plants in New Zealand. New Zealand Department of Scientific and Industrial Research.
  • Crowe, Andrew (2009). Which Native Forest Plant?. Auckland, New Zealand: Penguin Books. ISBN 978-0-14-300901-6.
  • Dawson, John; Lucas, Rob; Connor, Jane; Brownsey, P. J. (2019) [2011]. New Zealand's Native Trees. Nelson, New Zealand: Potton & Burton. ISBN 978-1-877517-01-3.
  • Eagle, Audrey (2006). Eagle's Complete Trees and Shrubs of New Zealand. Vol. 1. Wellington, New Zealand: Te Papa Press. ISBN 0-909010-08-0.
  • Forster, Georg; Dietrich, Joann. Christian. (1786). Florulae Insularum Australium: Prodromus Auctore Georgio Forster (in Latin). Gottingae [Göttingen, Germany]: Joann. Christian Dietrich. doi:10.5962/bhl.title.10725.
  • Friis, Ib (1993). "Urticaceae". Flowering Plants · Dicotyledons. Berlin, Heidelberg: Springer Berlin Heidelberg. doi:10.1007/978-3-662-02899-5_76. ISBN 978-3-642-08141-5.
  • Gibbs, George W. (1980). New Zealand Butterflies: Identification and Natural History. Auckland, New Zealand: HarperCollins. ISBN 978-0-00-216955-4 – via the Internet Archive.
  • Metcalf, Lawrie (2009). Know Your New Zealand Native Plants. Auckland, New Zealand: White Cloud Books. ISBN 978-1-77694-036-3.
  • Moore, Lucy Beatrice (1978). The Oxford Book of New Zealand Plants. Oxford University Press. ISBN 978-0-19-558035-8 – via the Internet Archive.
  • Nicolson, Dan Henry; Fosberg, Francis Raymond (2004). The Forsters and the Botany of the Second Cook Expedition: 1772–1775. A.R.G. Gantner Verl. ISBN 3-906166-02-3.
  • Salmon, John Tenison (1986). The Native Trees of New Zealand. Auckland, New Zealand: Raupo. ISBN 978-0-7900-0104-3 – via the Internet Archive.
  • Vennell, Robert (2019). The Meaning of Trees. Auckland, New Zealand: HarperCollins. ISBN 978-1-77554-130-1.

Journals

Websites

  • Wikimedia Commons logo Media related to Urtica ferox at Wikimedia Commons
  • Urtica ferox discussed on Critter of the Week, 28 April 2023
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