Imported plants can pack a punch in self-defence

For most creatures that walk, swim, waddle or flap their wings, plants are something to eat. They are nutritious, easy to find and even easier to catch since most of them can’t see you coming and don’t run away or bite back.

But plants haven’t survived for millions of years without some way of fending off the hordes of vegan predators and many have evolved complex defense mechanisms like thorns on cacti, barberry and roses, and oils on poison ivy and poison oak that are likely to give hungry herbivores and humans a poke or a nasty rash just for the fun of it.

But things get a little more serious in the defence department when it comes to some of those large tropical plants that have been adorning our local parks and gardens all summer, and if anyone is foolish enough to sample a fruit, nut or even a leaf from some of these ornamental exotics, the results can be fatal.

One of the most toxic offenders is the Castor bean (Ricinus communis), frequently planted with abandon for its huge palmate foliage and bright red spiked seed pods that appear in late summer and early fall. But the tasty-looking beans within the pods come loaded with an intense poison called ricin and it only takes a few of them to kill an adult if ingested.

Castor bean, photographed in a Toronto park. PHOTO: Steven Chadwick
Castor bean, photographed in a Toronto park.
PHOTO: Steven Chadwick

The plant is so toxic it was used to assassinate Bulgarian journalist Georgi Markov with a tiny ricin pellet that was injected ‘Bond style’ by a customized hypodermic umbrella while he was waiting for a bus in London. And castor caused a bit of panic in 2013 when postal screeners found dangerous amounts of a powdered ricin extract version in mail addressed to U.S. President Barack Obama.

Of course the plant does have some redeeming qualities. When the beans are processed into oil the toxic ricin mash is removed as waste and the product becomes Castor oil, that foul- and fishy-tasting concoction that my mother used to force feed me for minor ailments. And no wonder the stuff tasted bad – the castor oil I was gagging on was almost identical to a powerful non-petroleum-based lubricant (trademarked as Castrol) that was previously used in leaky rotary aircraft engines during the Red Baron era.

Datura (Datura stramonium) is another tropical annual with a poisonous attitude, and unlike castor, it can self-seed prolifically in our climate. It often wanders off to pop up in unlikely places like children’s playgrounds and sometimes the vegetable patch.

Datura can be dangerous in the wrong circumstances. Author Steven Chadwick photographed this example (with castor in the background) in a Toronto park two weeks ago. PHOTO: Steven Chadwick
Datura can be dangerous in the wrong circumstances. Author Steven Chadwick photographed this example (with castor in the background) in a Toronto park two weeks ago.
PHOTO: Steven Chadwick

All parts of this fast-growing sprawler are extremely toxic and hallucinogenic, especially the seeds contained in spiny golf ball-sized casings that ripen and split open at this time of the year. However, it’s an attractive annual that makes a great addition to a tropical border, with huge bell-shaped white flowers that grow upright rather than hang down like its close relative brugmansia. Fans of the plant affectionately refer to it as angel’s trumpet, but those in the know are more likely to call it devil’s horn, devil’s weed, devil’s snare, devil’s trumpet, devil’s cucumber, or the marginally devilish hell’s bells.

Oleander (Nerium oleander) might be sweet to look at and smell but don’t get your nose too close for a whiff of this elegant plant because its flowers, foliage and twigs can cause severe skin irritations and become a serious toxin if chewed or eaten in even moderate quantities.

Oleander is not planted as frequently as other tropicals but its foliage – often confused with olive – and spectacularly fragrant blossoms make it a common feature in many of the high-end formal garden parks around Toronto. Its seed pods are not as conspicuous as castor or datura so poisonings are usually confined to skin rashes from handling the plant.

Of course, it’s not just these tropical summertime beauties that use poisons to protect themselves. It’s a wild world out there and plenty of familiar native and non-natives use poisons as a defence as well. Wild parsnip, members of the nightshade family, bloodroot, and that monster that has been hogging all the press these days, giant hogweed can all bite back, so it would be wise to familiarize yourself – and especially children – with the characteristics of plants that can present a danger. If it can’t be identified, don’t touch and for heaven’s sake, don’t stop for a snack.


Steven Chadwick is a professional gardener and horticulturist, and longtime Beach resident

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