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.

If Poisoning Occurs

To find out what to do if you or someone you know has come in contact with a poisonous plant, call the Ontario Regional Poison Information Centre (1-800-268-9017 or 416-813-5900); it is open seven days a week, 24 hours a day.

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.

Climbing or Bittersweet Nightshade

[Solanum dulcamara]

[Solanaceae/Nightshade family]

Description: A woody vine up to 3 m tall. Small, purple flowers curl backward, exposing a “cone” of projecting yellow stamens from May to June. Green berries ripen to a translucent red in late August to October.

Where: Thickets, clearings, roadsides, neighbourhood parks and yards throughout south, central and eastern Ontario, west to east shore of Lake Superior

Toxicity: The leaves and unripened fruit of bittersweet nightshade contain steroidal alkaloids, although ripened fruit seldom has traceable amounts. Reports of the toxicity of this plant vary, some saying that eating as few as 10 berries can cause a fatality, while others put the number at 200.

White Baneberry

[Actaea pachypoda]

[Ranunculaceae/Buttercup family]

Description: Smooth-stemmed, attractive perennial 30 to 80 cm tall. The fruit – brilliant white berries with a black dot at their tips – gives the plant its nickname, doll’s eyes. Sharp-toothed leaflets about 10 cm long are arranged in groups of three.

Where: Rich forests in southern, central and western Ontario, north to the southern limits of the boreal forest

Toxicity: All parts of the baneberry, like other buttercups, possess the glycoside ranunculin, which is converted to the irritant protoanemonin when ingested. It causes distress to the mouth and throat, stomach cramps and vomiting.


[Arisaema triphyllum]

[Araceae/Arum family]

Description: Scarlet berries form a dense club-shaped cluster in late summer and autumn. Small, hidden flowers are borne on a spike-like spadix (the jack) surrounded and hooded by a green to purple striped spathe (the pulpit) located beneath the leaves.

Where: Moist woods and thickets in south, central and western Ontario, north to the southern limits of the boreal forest region

Toxicity: Children are often attracted to the scarlet berries that, like the rest of the plant, including its stem and roots, contain needle-like crystals of calcium oxalate that cause a severe burning sensation in the mouth, throat and mucous membranes.

Poison Ivy

[Rhus radicans/Toxicodendron radicans]

[Anacardiaceae/Cashew family]

Description: A creeping plant up to 30 cm tall, sometimes with aerial roots climbing high into the trees or onto walls. Alternate compound leaves with three leaflets and small, inconspicuous flowers that bloom from June to early July. Hard, berry-like fruit turns white in late summer and remains on the stalks into winter.

Where:  Throughout southern Ontario; less common in northern and northwestern regions of the province

Toxicity: Effects of direct contact with poison ivy can range from mild skin irritation and redness to oozing blisters, severe itchiness and even fever. The allergen responsible is urushiol, an oily mixture found in the sap throughout the plant. Beware: even indirect contact with poison ivy can produce these effects, as urushiol sticks to clothing, footwear, garden tools and pet hair.


[Sanguinaria canadensis]

[Papaveraceae/Poppy family]

Description: Single stem from 5 to 15 cm in height. Single white flower blooms from April to early May; pale, lobed green leaf doubles in size after blooming.

Where: Rich forests of southern and central Ontario, north and west of the Great Lakes to the limits of the boreal forest

Toxicity: Long used by First Nations people as a skin dye, bloodroot contains alkaloid substances similar to the opium poppy. Sanguinarine is one of the more potent toxic ingredients. Ingestion results in tunnel vision, vomiting, diarrhea, irritated mucous membranes, fainting and possibly coma. Scientists are now studying sanguinarine as a possible anti-cancer agent.


[Podophyllum peltatum]

[Berberidaceae/Barberry family]

Description: Umbrella-like in configuration and about 45 cm tall. A single, nodding flower, hidden by leaves, composed of five to nine waxy white petals and many stamens; blooms from May to June. Large yellow berries, 2 to 5 cm long, follow in mid-August to September.

Where: Often in large colonies in rich forests in southern Ontario to north Georgian Bay region eastward to Ottawa–St. Lawrence rivers region

Toxicity: First Nations peoples and pioneers used mayapple roots to alleviate a variety of aliments. Currently, podophyllotoxin, the primary toxin of mayapple, affects cell division. It is now used as an anti-cancer agent in chemotherapy.


[Cicuta maculata]

[Apiaceae (Umbelliferae)/Parsley family]

Description: Up to 2.2 m tall. Small, white flowers shaped like an inside-out umbrella, in bloom from July to August. Alternating, coarsely toothed leaves and a stout, green stem spotted with purple that exudes a yellow, oily liquid when cut.

Where: Wet habitats – marshes, swamps, stream banks, ditches, moist thickets and meadows – throughout Ontario

Toxicity: Water-hemlock is North America’s most deadly plant, poisonous to livestock and humans. One bite can kill an adult human. All parts of the plant contain cicutoxin, a toxic alcohol that attacks the central nervous system. Symptoms, which appear within 15 minutes of ingestion, include extreme salivation, violent convulsions, intense abdominal pain and delirium. Coma and respiratory failure follow from 30 minutes to eight hours later. Water-hemlock closely resembles wild edibles in the parsley family, especially wild parsnip and wild carrot.

Black Cherry

[Prunus serotina]

[Rosaceae/Rose family]

Description: Bark resembles burnt corn flakes with nearly black squarish scales curving outwards at the edges (young bark is smooth with horizontal streaks called lenticels). Blooms in May and June when loose clusters of white, five-petalled flowers appear amid oval leaves. Drooping clusters of dark-coloured, fleshy berries appear in late August to September.

Where: River valleys, dry to moist woods in a variety of soils in the Carolinian and mixed forest regions of southern, central and eastern Ontario

Toxicity: The seeds, leaves, twigs and bark of black cherry contain chemical compounds called cyanogenic glycosides. When ingested, these chemicals are transformed into hydrocyanic acid (HCN ), a fastacting, deadly toxin. On average, 100 g of black cherry leaves contains 212 mg of HCN . A lethal dose for cattle is 2 mg per kilogram of body weight. For humans, a smaller amount is fatal – 0.5 mg per kilogram of body weight. Symptoms, which appear swiftly and with little warning, include loss of voice, muscle spasms, respiratory failure, coma and death.

White Snakeroot

[Eupatorium rugosum]

[Asteraceae/Aster or composite, family]

Description: One to 1.5 m tall. Flower head composed of 10 to 30 tiny bright white flowers that bloom in July through to October. Smooth leaves sprout from slender stalks that are slightly heart-shaped at the base, long-pointed at the tip and coarsely toothed.

Where: Moist woods, thickets and fields throughout Ontario south of the Canadian Shield

Toxicity: So-called milk sickness, a condition brought about by drinking milk from cows suffering the “trembles,” caused thousands of deaths in the 1800s. The source of trembles and milk sickness remained unknown until 1928 when an aromatic alcohol – tremetol – was found in the leaves and stem of white snakeroot. People who drank tainted milk suffered tremetol poisoning – muscle tremors and weakness, irregular heartbeat, red-brown urine, coma and death. Improved animal husbandry, along with pooling milk from many producers, has eliminated the risk of milk sickness.


Field guide

Steven Foster and Roger Caras. Venomous Animals and Poisonous Plants. Peterson Field Guide Series. Boston: Houghton Mifflin Company, 1994


Canadian Poison Plants Information System []

Ontario Regional Poison Information Centre []

Dan Schneider and Peter Pautler are resource interpreters with the Grand River Conservation Authority.