Ontario's natural landscape is bursting with vibrant flora, but beneath the beauty can lurk hidden dangers. Many common plants harbour toxins that can cause everything from mild irritation to serious health problems.
Whether you're an avid gardener or a nature enthusiast, familiarizing yourself with these botanical bad boys is essential. Here's a list of some of the most common poisonous plants found in Ontario:
Poison Ivy (Toxicodendron Radicans):
The infamous "leaves of three, let it be" saying serves as a warning against this dreaded plant, poison ivy. It is widespread throughout southern Ontario and reaches north approximately as far as Cochrane and Kenora. It is found most abundantly, however, south of a line from the north shore of Lake Huron through North Bay. Its glossy green leaves, arranged alternately, consist of three leaflets, with the middle one sporting a notably longer stalk. The leaf edges can be smooth or toothed. Poison ivy thrives along forest edges, in meadows, forest openings, and trails. However, despite its innocuous appearance, it packs a potent punch with urushiol, a strong antigen triggering allergic contact dermatitis in 60 to 80% of those exposed. This oil resin can linger on objects like clothing, shoes, or pet fur, transferring the allergen to the skin upon contact.
Stinging Nettle (Urtica dioica L., Urticaceae):
Stinging nettle thrives during the summer and fall, often reaching heights of up to one metre. Recognizable by its heart-shaped leaves and pink-and-yellow flowers, the plant is covered in fine hairs that can irritate the skin. You’ll often find it growing in floodplains, old pastures, woodlands, and along stream banks. Though long valued as an herbal remedy, stinging nettle can cause a temporary rash if touched. If contact occurs, rinse the area right away with cold water and soap, remove any remaining hairs, and keep the skin clean to ease the discomfort.
Giant Hogweed (Heracleum Mantegazzianum):
Reaching towering heights of 4 to 5 meters, giant hogweed boasts a reddish-purple stem with a diameter ranging from 5 to 10 centimetres. Its flowering period spans from June to September, showcasing impressive clusters of flowers up to 1.1 meters wide, each cluster bearing 30 to 20 flowers. This invasive species proliferates along roadsides, trails, and stream banks. However, contact with giant hogweed can lead to severe skin burns. Its sap contains furocoumarins, triggering serious skin inflammation upon sun exposure, causing significant discomfort and potential long-term damage.
Wild Parsnip (Pastinaca Sativa):
Wild parsnip, standing tall between 50 and 150 centimetres, boasts compound leaves arranged alternately along its stem, with mitten-shaped leaflets. Its yellow flowers form a flat-topped umbrella-like cluster, visible from late May through early fall, exuding a distinct parsnip fragrance. Similar to giant hogweed, wild parsnip harbours a toxic sap that triggers phytophotodermatitis upon skin contact followed by sunlight exposure, leading to painful burns, blisters, and skin discoloration.
Pokeweed (Phytolacca americana L.):
Pokeweed, found in meadows, woodland edges, and waste areas across Southwestern Ontario, features a distinctive red trunk-like stem that hollows out as the plant matures. Its large egg-shaped leaves, measuring up to 25 centimetres long, are dark green and alternate along the stem, each attached by a red stalk. The flowers range from green to white, while the fruit starts green and darkens to a deep purple or black when ripe. However, despite its aesthetic appeal, pokeweed poses significant risks as it's poisonous to both humans and animals. Ingesting pokeweed can lead to symptoms such as sweating, blurred vision, abdominal pains, weakness, vomiting, and even unconsciousness.
Spotted Water Hemlock (Cicuta Maculata):
The spotted water hemlock, reaching heights of up to 2.2 meters, showcases small white flowers resembling inverted umbrellas that bloom between July and August. Its stout green stem, speckled with purple spots, oozes a yellow oily liquid when cut. This plant's habitat spans marshes, swamps, stream banks, ditches, moist thickets, and meadows throughout Ontario. However, despite its picturesque appearance, it harbours cicutoxin, a toxic alcohol targeting the central nervous system. Ingesting this toxin leads to rapid onset of symptoms such as excessive salivation, violent convulsions, severe abdominal pain, and delirium. Within 30 minutes to eight hours, affected individuals may progress to coma and respiratory failure.
Common Moonseed (Menispermum Canadense):
Common moonseed, also known as Canada moonseed or Menispermum canadense, is a poisonous, woody vine native to much of eastern North America, including Ontario. All parts of the plant are toxic—especially the fruit—and ingestion can cause serious symptoms such as convulsions. It is often mistaken for wild grapes due to its similar-looking fruit. The key difference lies in the seeds: moonseed berries contain a single, crescent-shaped seed, while grape seeds are small and round. Common moonseed can be identified by its broad, palmately lobed leaves and its habit of twining up trees, fences, and other structures.
As you venture into Ontario's great outdoors, keep this list in mind to ensure a safe and enjoyable experience. Remember, when in doubt, it's best to admire these plants from a distance and avoid direct contact to protect yourself from their harmful effects.
