Don’t let these poisonous plants bewitch you
Iceland poppy, larkspur, lily of the valley and daphne: all so pretty, but along with dozens of other plants found in our gardens, all toxic to both people and animals. Eating daphne can cause anything from drooling, vomiting, and inflamed kidneys to arrhythmia, seizures, coma and even death. As with daphne, all parts of the Iceland poppy are toxic, tragically for two local horses who died after eating a rather large portion last century.
Sometimes it is just part of a plant that is toxic, often it is all. Some toxins must be eaten to have an effect, others are contained within the sap or the thorn and only released on contact. The National Poisons Centre, based in Dunedin, released the following list of poisonous plants most enquired about by parents over 10 years in the early 2000s. The appearance and position of a plant on the list more likely reflect its prevalence and reputation rather than its toxicity.
What are some of the most poisonous plants in New Zealand?
1. Black Nightshade
Topping the list was black nightshade, often confused with deadly nightshade. While the latter lives up to its name, it is extremely rare in New Zealand. Black nightshade, on the other hand, is common and only moderately toxic; its berries when ripe and black are not toxic at all. Other poisonous members of this solanum family include poroporo, whose berries are to be avoided when green or yellow but are fine when fully ripe, and potatoes. While the potato tuber itself contains glycoalkaloids, the highest concentrations of the toxins are in the leaves, flowers, eyes, sprouts and greened skin. Numerous cases of mass poisoning and death around the globe over the years have been traced back to eating green potatoes.
Black nightshade is common and only moderately toxic; its berries when ripe and black are not toxic at all.
2. Arum Lily
Like its cousins in the zantedeschia family, which includes calla lilies, every part of the arum lily is toxic. When ingested it can cause burning all the way down the digestive system, breathing difficulties, shock and death.
When ingested the arum lily can cause shock and death.
3. Kowhai Tree
Only the seeds of the kōwhai are poisonous – though highly so. And only if they are crushed or ground before eating. Otherwise, they pass through the body intact to continue their natural cycle of germination.
The kowhai seeds need to be consumed in large quantities to effectively poison a person.
The milky sap of euphorbia is a skin irritant and if even a tiny amount gets into an eye, extreme pain, blurred vision and temporary blindness can follow. One euphorbia, the pencil cactus, is a popular houseplant – despite having the dubious honour of possessing the most irritating plant substance known.
5. Peace Lily
The peace lily entered our offices and homes in great numbers in the 1990s, propelled by its reputation as an air purifier. Unfortunately, awareness of its toxicity did not accompany its arrival. Along with fellow houseplants dieffenbachia, alocasia and philodendron, the lily contains tiny crystals that cause immediate irritation to the mouth and beyond. Possibly because of their size, cats are more severely affected, with death not uncommon.
Because of their size, cats are more severely affected by the peace lily crystals.
Agapanthus are another very common garden plant, and all parts of which contain saponin, which can cause gastrointestinal irritation but rarely severe toxicity or death in humans.
Agapanthus can cause gastrointestinal irritation.
7. Stinking Iris
While specifically the stinking iris with its bright orange berries so attractive to children was the seventh most common cause of concern for parents, almost all members of the iris family are poisonous, causing vomiting and worse.
Almost all members of the iris family are poisonous.
Both rhubarb stalks and leaves contain oxalic acid, but in much higher levels in the leaves making them toxic. The acid can build up in the organs and lead to kidney stones and kidney failure.
As rhubarb leaves are high in oxalic acid, be careful not to eat too many.
Another edible with a will to kill is taro. All parts of it are poisonous unless cooked properly. Even eaten partially cooked will burn the throat.
All parts of taro are poisonous unless cooked properly.
Oleander is classified as extremely toxic to humans and animals, with a single leaf being enough to kill an adult. Its main toxin paralyses the vagus nerve, resulting in rapid death. Stock are particularly vulnerable.
A single leaf of oleander is enough to kill an adult.
In Japan, between 2009 and 2019, 195 people died from daffodil poisoning, many after mistaking them for onions. The effect is almost immediate with vomiting, nausea and, of course, death in extreme cases. Other toxic bulbs include autumn crocus, hyacinth, gladioli, snowdrop, snowflake, tulips, nerine, crinum and amaryllis.
Ingesting daffodils can cause death, in the most extreme cases.
The most famous death from hemlock was the suicide of Greek philosopher Socrates, nearly 2500 years ago; and it is still rated as one of the world’s most poisonous plants. Quite common throughout New Zealand, the easiest way to distinguish it from parsley is its foul smell and purple markings on the stem.
Hemlock is considered one of the world’s deadliest plants.
13. Karaka berries
The fleshy outer part of karaka berries is not poisonous; it is the hard kernel that must be shunned unless detoxified by a long and complicated method perfected by Māori.
Karaka berries are a favourite of native birds, especially the Kererū, but the kernels inside the berries are toxic to humans.
The same cardiac glycosides found throughout a foxglove plant and used to make heart stimulant drugs are those that make it so poisonous; the seeds especially so. Main poisonings overseas appear to occur through confusion with comfrey leaves.
The cardiac glycosides found in foxgloves can result in severe poisoning.
Ongaonga is New Zealand’s most famous poisonous plant, and the only native known to have killed anyone. Its needle-like hairs impart intense localised pain and inflammation as they release triffydin into the body, enough of it and loss of motor movement, paralysis, drop in blood pressure, convulsions, blurred vision, confusion and even death may result.
Ongaonga is the only New Zealand native known to have killed anyone.
Six houseplants toxic to pets:
Although indoor plants do a great job at livening up a room, if you have pets at home they could potentially do more harm than good.
Aloe vera can cause vomiting, diarrhoea and tremors.
Ficus can cause oral irritation, drooling, vomiting and difficulty swallowing.
Jade plants (aka money plant) can cause vomiting, depression and incoordination.
Monstera deliciosa can cause intense burning and mouth irritation.
Sago palm can cause abdominal pain, seizures, coma and liver failure.
Snake plants (aka mother-in-law’s tongue) can cause nausea, vomiting and diarrhoea if ingested.
Other common toxic plants:
- Bleeding heart
- Morning glory
- Lily of the Valley
Seven non-toxic houseplants that also purify the air:
Indoor plants not only drastically improve air quality in your home or office, but they can reduce stress and make you happier.
- Boston fern
- Dendrobium orchid
- Moth orchid
- Rubber plant
- Spider plant
- Sword fern.
Text Mary Lovell-Smith