Story: Poisonous plants and fungi
Page 1 – Poisonous native plants
Few people in New Zealand have died from plant and fungal poisoning, but each year about 75 people need hospital treatment. Reports of mushroom poisoning in New Zealand have been increasing since the early 1990s.
Why are some plants and fungi poisonous?
Plants and fungi make a wide array of chemicals to ward off bacteria, other fungi, insects and browsing mammals, and to protect their patch from competitors. Some of these chemicals are toxic to humans or animals.
In case of poisoning
If someone shows signs of poisoning, and you think they have eaten a poisonous plant, dial 111 for an ambulance. Keep any parts of the plant or fungus for an expert to identify.
Tree tutu and ongaonga or tree nettle are the only New Zealand native plants known to have killed humans by poisoning.
The small tree tutu (Coriaria arborea) is found throughout the country, especially on bush margins and alongside streams. Except for its swollen petals, all parts of the plant are poisonous.
Around 1900, New Zealand chemists identified tutin as the poison. This acts on the central nervous system, causing convulsions and breathing problems that may lead to death. There have been few cases of human poisoning by tutu since 1900, although one man died in 1989.
Tree nettle (ongaonga)
Also known by its botanical name, Urtica ferox, this killer plant is well-documented. Like all nettles, it is covered in stinging hairs that put poison into the skin of a person or animal that brushes against it. The plant grows in coastal and regenerating shrublands up to 600 metres above sea level, where it may form dense thickets up to 2 metres tall.
On Boxing Day 1961 two young men hunting in the Ruahine Range stumbled through a patch of tree nettle and received a number of stings on their limbs. Within an hour one of them had difficulty in walking and breathing, and then lost his sight. He died five hours later in hospital. His friend had similar symptoms, but recovered. Although this is the only fatal incident on record, a number of people have been very ill for two to three days after being stung.
Other poisonous natives
Some other native plants are poisonous:
- Kōwhai (Sophora species) – its yellow seeds are poisonous if chewed.
- Tītoki (Alectryon excelsus) – contains cyanide-producing poisons.
- Ngaio (Myoporum species) – has poisonous leaves.
- Karaka (Corynocarpus laevigatus) – has a poisonous seed in its fleshy orange fruit.
- Poroporo (Solanum aviculare, S. laciniatum) – their unripe green berries are poisonous. The early European settlers made jam from the ripe orange berries.
- Tūrutu, blueberry lily (Dianella nigra) – their violet-coloured berries were implicated in the death of an infant in the late 1800s.
It is most unlikely that someone would eat enough of these plants to die or become seriously ill.