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''Urtica ferox'', commonly known by its Maori name ongaonga, is a nettle that is endemic to New Zealand. It is sometimes known as the "tree nettle", "Taraonga", "Taraongaonga" or "Okaoka". Unlike other herbaceous species in the ''Urtica'' genus, ongaonga is a large woody shrub. It has woody stems and unusually large stinging spines that can result in a painful sting that lasts several days. The shrub can grow to a height of with the base of the stem reaching in thickness. The pale green leaves are very thin like a membrane, the surface of the leaf, stems and stalks are covered in stiff stinging hairs can grow up to long. These spines are prominent along the salient mid-vein and leaf margin. The leaves range from in width and in length, these are oppositely arranged and there are two stipules per node. The leaf shape is ovulate-triangulate with a serrated leaf margin each bearing a spine of up to . The spines covering the leaf surface, stem and stalk are generally no larger than in length, the spines on the older darker bark are smaller and softer, these don't cause a sting. This nettle is winter deciduous in cold climates, evergreen in mild climates and can lose its leaves in drought conditions if it is growing in shallow soils. The toxin present in the spines is triffydin (or tryfydin). This toxin contains histamine, serotonin and acetylcholine, the last of which causes powerful stimulation of the parasympathetic nerve system. Multiple stingings can have a very painful reaction which causes inflammation, a rash, itching, and in high concentrations loss of motor movement, paralysis, drop in blood pressure, convulsions, blurred vision and confusion. The toxin from 5 spines are enough to kill a guinea pig. There has been one recorded human death from contact—a lightly clad hunter who died five hours after walking through a dense patch.〔(''Poisonous native plants'' ), Te Ara Encyclopedia of New Zealand〕 Acute polyneuropathy can occur due to ''U. ferox'' stings.〔Kanzaki M, Tsuchihara T, McMorran D, Taylor P, Hammond-Tooke GD.,"A rat model of Urtica ferox neuropathy." ''Neurotoxicology''. 2010 Dec;31(6):709-14〕 In Maori folklore, Kupe was said to have placed several obstacles to hinder pursuers whose wives he had stolen, one of which was the ongaonga. Ongaonga is the main food plant for larvae of the New Zealand red admiral butterfly or kahukura, ''Vanessa gonerilla''. ==Distribution== The tree nettle is an endemic species to New Zealand which inhabits sub-tropical and temperate regions, the plant is very common in the North Island but limited in the South. In the South it's commonly found on the West Coast and on Banks Peninsula, the plant is not commonly found east of Otago where the climate is much drier. The tree nettle can also be found on Stewart Island. The shrub commonly inhabits coastal and lowland areas at altitudes between sea level and 600m above sea level. It can be found on its own or in dense thickets and is often found growing along forest margins. It prefers well lit environments so suits stock damaged bush, in tree fall gaps and on steep and unstable slopes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Urtica ferox」の詳細全文を読む スポンサード リンク
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