Dangers lurk in our own backyard. Most hospital admissions from plant poisoning are young children who have eaten or touched a plant in a local garden. Most of these poisonings are non-fatal.
Many poisonous plants in New Zealand have been introduced for horticultural reasons. Only nine native plants appear on Landcare Research’s list of 93 plants and plant groups that pose a danger to children. In a study of hospital admissions from 198 to 1998 for plant poisoning, 93% of the plants identified were introduced species.
Top of the list for hospital admissions are members of the potato and nightshade family (Solanaceae). Many admissions are for suspected poisoning by deadly nightshade (Atropa belladonna), but this plant is very uncommon in New Zealand, and the cause is usually black nightshade (Solanum nigrum). This very common weed is often mistakenly called deadly nightshade, although it is much less toxic.
Jerusalem cherries (Solanum diflorum and S. pseudocapsicum) are a more common danger. One child has died and several have become ill after eating the fruit. The small shrubs have attractive bright red berries and are often planted for winter colour. Both species have been spread by birds into nearby bush.
Plants of the arum family (Araceae) are the second largest group causing hospital admissions. Included in this family are:
- calla lily (Zantedeschia aethiopica), known as arum lily in New Zealand
- Italian arum (Arum italicum)
- dumb cane (Dieffenbachia species)
- taro (Colocasia esculenta)
- elephant’s ear (Alocasia brisbanensis), also known as kape or ’ape by Pacific Islanders.
All parts of these plants are poisonous and cause severe irritation of the mouth and throat if swallowed. Most arum poisonings occur when children eat the bright fruit spikes of calla lily. This is widely grown in home gardens, and a common weed. Taro leaves and tubers can be eaten only after prolonged cooking.
Datura stramonium (thorn apple) and the related angel’s trumpet (Brugmansia candida) are two of the most dangerous plants in New Zealand. These tall shrubs have hanging, trumpet-shaped flowers and are grown as garden specimens. Datura also grows as a weed. It is sometimes eaten by people wanting to experience hallucinations, caused by the plant’s powerful alkaloid chemicals. These have other side-effects that can be lethal: they over-stimulate the heart and act as powerful muscle relaxants. In New Zealand datura has been responsible for a number of admissions to intensive care, and has indirectly caused at least two deaths from drowning.
Pretty and poisonous
The most likely plants to cause severe poisoning in New Zealand are (in alphabetical order):
- castor oil plant (Ricinus communis)
- datura or thorn apple (Datura stramonium)
- hemlock (Conium maculatum)
- Jerusalem cherry (Solanum diflorum and S. pseudocapsicum)
- laburnum (Laburnum anagyroides)
- lily of the valley (Convallaria majalis)
- yew (Taxus baccata).