Story: Poisonous plants and fungi
Page 2 – Poisonous plants used for food
Māori used some poisonous plants for food, processing them to make them safe. Usually the plant was cooked for a long time, and then soaked in water.
Raw kernels of karaka fruit are poisonous and may cause paralysis. However, Māori gathered karaka berries as one of their staple foods. They would bake and soak them before making them into a floury cake that was safe to eat.
One of New Zealand’s early chemists, William Skey, isolated a bitter compound (karakin) from the kernels. He suspected this was the poison that caused convulsions and paralysis. It was later confirmed that karakin was toxic to birds, bees and mammals, but was destroyed when heated for an hour at 100°C.
The Polynesian ancestors of Māori brought taro (Colocasia esculenta) to New Zealand. All parts of the plant are poisonous when raw or partly cooked, and cause severe irritation of the mouth, tongue and throat. The leaves and tubers are safe after prolonged cooking.
Bracken (Pteridium esculentum) is known to be carcinogenic (cancer-causing). This common fern causes cancers in animals, and is thought to cause throat and stomach cancers in Japanese people, who eat the young fronds.
The rhizomes (underground plant stems) of this widespread fern were an important food for Māori. They soaked then roasted the rhizomes, and beat the baked product to produce a starchy flour.
Maori made an alcoholic drink (tutu beer or tutu wine) and a pudding from the fruit of the tutu tree. They were careful to strain out the toxic seeds. Not so knowledgeable were four French sailors, who died in the mid-1830s after eating tutu berry pudding.
Tutu wine packed a fair punch. In the early days of European settlement, two reverend gentlemen, Canon J. W. Stack and Bishop H. J. C. Harper, took a little drink of tutu wine. Stack later reported that they soon lost all feeling in their extremities and could hardly keep their balance. Their vision became impaired, and they felt they were being poisoned. But then the strange sensations passed, and feeling came back in their limbs.
Honeydew is secreted from the rear end of tiny sap-sucking insects (passion-vine hoppers, Scolypopa australis) that feed on the poisonous tutu plant. Toxic honey is produced by bees that feed on this honeydew. The honey contains tutin and hyenanchin (a related toxin), and is extremely dangerous.
Outbreaks of honey poisoning have been documented since the early 1900s. The main areas are the Coromandel, eastern Bay of Plenty and Marlborough Sounds. Honey is most likely to be contaminated during hot dry summers, when vine hopper numbers are high. Beekeepers remove their hives from risk areas when toxic honeydew is abundant.
Rhubarb and potato
Parts of some common food plants are poisonous. Rhubarb (Rheum rhabarbarum) stems are edible when cooked, but the leaves are poisonous. Green and sprouting tubers of potato (Solanum tuberosum) contain toxic alkaloids and should not be eaten. Potatoes are normally stored in the dark to reduce their exposure to sunlight (which causes greening). In New Zealand one person has died after eating potato berries, the green fruit that grows on the potato stem after it flowers.