Dangerous plants

We don’t often think of our beautiful gardens or parks as posing a risk for our health. But plants that are pleasing to the eye can also be dangerous — or in some cases, even deadly.

Experts warn to be on the watch for giant hogweed (heracleum mantegazzianum) — which can burn the skin, pose a risk for cancer and birth defects and cause temporary or even permanent blindness.

According to media reports, hogweed has been spotted in Newfoundland, New Brunswick, Quebec, southwestern Ontario, Alberta and British Columbia. Although the plant — which originates in parts of Eastern Europe and Central Asia — has been in Canada for many years, most provinces have not authorized an official policy to destroy it because it does not encroach on agriculture.

But the weed’s clear, watery sap can be very dangerous for humans.

“What it does to you is pretty ugly,” Jeff Muzzi, an Ontario forestry manager and weed inspector, told the National Post. “It causes blisters. Large blisters and permanent scarring. What’s left over looks like a scar from a chemical burn or fire.”

And it only takes a tiny trace of sap to damage the cornea of the eye, causing temporary or even permanent blindness. The sap, which is all over the plant, also contains carcinogenic and teratogenic chemicals (furocoumarins) that can cause cancer and birth defects. The plant’s toxicity is especially potent during the daytime, since sunlight helps to bond the sap to the skin.

Often confused with other native plants

True to its name, giant hogweed can reach a towering height of 4-5 metres (13-17 feet). Its stem, which is purple-reddish in colour or has purple spots, has a diameter of 5-10 centimetres (2-4 inches). The plant is known for its small white flowers that form an umbrella-like head — in fact, a single plant can contain more than 80,000 flowers. When young, however, it can be much shorter and without flowers.

Giant hogweed is often confused with other native plants such as cow parsnip or Queen Anne’s lace — which also have umbrella-like flowers — but are smaller and do not pose the same health risks.

Native to Caucasus Region and Central Asia, hogweed was brought to Europe and North America in the 19th and 20th centuries as an ornamental plant. Experts say it probably arrived in Ontario in 1949.

If you believe you have spotted a giant hogweed either in a public natural area or your own garden, experts warn not to touch the plant, but to notify the appropriate authorities or professionals for removal. Also be sure to keep children and pets away from the plant. If you should inadvertently touch a giant hogweed, wash the affected area immediately with soap and cool water. Avoid sunlight and seek medical attention.


Other garden and woodland hazards

Giant hogwood is certainly not the only plant that can cause pain or discomfort — or worse — if you happen to stumble across it. From thistle and stinging nettle to poisonous native weeds, some plants can be more than a nuisance — they can be downright dangerous.

Water hemlock, for example, is considered by the Centers For Disease Control and Prevention (CDC) to be one of the world’s most poisonous plants. Commonly found in the wild, it is often mistaken for a type of parsley. Eating even a small amount of the plant can be deadly — but you may not need to actually eat it to become very sick. Poison hemlock was reportedly responsible for sending a woman from Washington to the hospital after simply touching the plant and breathing in its pollen while digging in her garden, according to media reports.

Even some of the most beautiful and commonly used garden plants are poisonous and can cause harm to people and animals if ingested. Some of the plants — which should be admired but not eaten — include Lily of the valley, daffodils, wisteria, azaleas, rhodendrons, foxglove, delphiniums and hyacinths. (See a listing of poisonous plants and noxious weeds found in Canada.)

Additional sources: Centers for Disease Control and Prevention; The National Post; weeds.ca; kval.com; Wikipedia; LiveScience.com

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