Plant that May Strike You Blind Found in Michigan

Giant hogweed, a member of the carrot family, resembles Queen Anne’s lace and cow parsnips, both benign plants. Hogweed is anything but that. (Photo by Fritz Geller-Grimm via Wikimedia/Creative Commons)

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It turns out that running into a Michigan black bear might be the least scary thing that can happen during a hike in the woods.

What you really want to beware of is Heracleum mantegazzianum, commonly known as giant hogweed, a dangerous plant that can cause permanent blindness. It was discovered recently in Pennfield Township near Battle Creek, the Detroit Free Press reports.

Giant hogweed, a biennial which can grow up to 12 feet tall and whose pretty white umbrella-shaped blossoms resemble the benign Queen Anne’s lace and cow parsnip, is nothing to mess with.

Hogweed’s sap causes what is called phytophotodermatitis. And if the prospect of weeping blisters and long-lasting scars isn’t enough to scare you back into civilization, the sap can also cause blindness if it comes in contact with the eyes.

The noxious weed has been removed from the site where it was discovered in south central Michigan. Still, that’s no guarantee the plant known for its hardiness won’t show up again, the Calhoun County Public Health Department warns. The site will be monitored for several years.

If you think you’ve brushed up against giant hogweed, wash off your skin with soapy water, immediately flush your eyes with water and seek medical attention right away, health officials advise. The tricky thing about the weed is that it could take up to 48 hours for the symptoms to appear.

“Giant Hogweed is a public health hazard that ranks up there higher than poison ivy, poison oak and poison sumac in respect to its potential to harm humans,” the Michigan Department of Agriculture & Rural Development says on its website.

The plant, native to the Caucasus Region and Central Asia, was introduced to Britain as an ornamental plant in the 19th century. Its first appearance in the United States was about a century ago when it was imported as by gardeners attracted to its sweeping stature.

The hardy seeds can float miles downstream for three days and germinate anywhere in sunny, damp soils along waterways, and they’re easily spread by wind, animals and gardeners oblivious to the plant’s toxicity who have shared the seeds.

Large colonies of hogweed can form from a single plant and, once established, it can take up to five years to completely eradicate due to regrowth from seeds and roots. The U.S. Forest Service lists giant hogweed as a noxious weed, and the Michigan Department of Resources adopted a search-and destroy policy in 1998 to stop the spread of the goliath plant.

Hogweed has been found in more than a dozen U.S. states, mostly in the Northeast, but also as far west as Washington and Oregon and as far south as North Carolina. It was discovered in Michigan in 1991, when the closest source of contamination was in Ontario.

There’s some good news. It’s still relatively rare in the state, according to Michigan State University Extension.

MSU Extension offers the following tips for recognizing giant hogweed:

• Giant hogweed is a biennial or perennial herb capable of reaching 6 to 12 feet in height in Michigan. The best time to identify giant hogweed is during flowering. Plants sprout in early spring from seed or tuberous rootstocks. Plants can quickly form a solid canopy and displace native vegetation.
• Stems are 2 to 4 inches in diameter, hollow, stout and ridged with purple blotches and coarse, white hairs. Stems may approach 12 feet in height in Michigan.
• Leaf petioles (leaf stems) are hollow, purple-blotched and sometimes nearly solid purple near the base. Coarse, white hairs are especially prominent circling the stem at the bases of the petioles.
• Leaves are very large – up to 5 feet across. Lower leaves are compound with three large, deeply cut leaflets. Each leaflet has deep, irregular lobes and coarse, sharp teeth on the margins. Upper leaves are similar in shape, smaller, often not divided but simply deeply three-lobed. Hairs on the underside are stiff, stubby and approximately 0.25 mm long, and they may not be visible to the naked eye. The leaf underside looks smooth and scaly.
• Flowers are white, clustered into a large, compound umbel with a flat bottom and gently rounded top. Umbels can be 2.5 feet wide. The plant flowers from June to August in Michigan.

Click here for some tips on distinguishing hogweed from its look-alikes.

If you think you have found giant hogweed, send photos to Michigan State University via e-mail at [email protected], or call MDARD at (800) 292-3939.