by Dan Scheider and Peter Pautler
A terrible story in the Schneider household goes back to the 1800s. Two young boys, on their way to bring in the cows, mistook the roots of water hemlock for tasty wild parsnip and enjoyed a snack. Some time later, one boy was found dead on the doorstep, the other in the kitchen.
Why are some plants poisonous? What evolutionary purpose does toxicity serve? After all, many plants depend on insects and other animals to disperse their seeds and pollen. Yet plants must also protect life-giving leaves, stems and roots from a host of hungry herbivores. To this end, some plants have thorns, while others have evolved a chemical defence.
Brush against a nettle, and stinging toxins are injected into your skin. Touch the sap of poison ivy, and, if you are allergic to it, you will be driven to distraction by a rash that defines the word itchy. Chew a jack-in-the-pulpit, and your mouth feels like it is on fire as needle-like crystals penetrate tender tissue.
Some animals have a tolerance for poisonous plants and may even benefit from their toxins. By ingesting and concentrating the toxin from milkweed, for example, monarch butterflies and other insects acquire a bad taste. The monarch’s orange-and-black coloration serves as a warning to insectivores.
Humans also benefit from certain poisonous plants, since their toxins may have important medicinal uses. Mayapple, for instance, provides us with an anti-cancer medication, and foxglove, a widely planted European flower, is the source of digitalis, a treatment for heart ailments.
Ontario’s many poisonous plants vary widely in toxicity, from merely annoying to extremely dangerous if eaten. Some grow wild, while others are common house and garden plants, such as American yew and poinsettia. Distinguishing poisonous from harmless plants is difficult, although their names – bittersweet, dogbane and poison ivy, among them – can be a clue to their nature. Your best defence against accidental poisoning is to familiarize yourself with the plants in your area. Take note: poisonings occur most often in autumn when berries and mushrooms are abundant.
Dan Schneider and Peter Pautler are resource interpreters with the Grand River Conservation Authority.