It's huge, it's extremely dangerous, and it's spreading. The giant hogweed (Heracleum mantegazzianum) contains a corrosive sap that causes severe rashes, third-degree burns, and even permanent blindness if you get the photosensitive chemicals on your skin or in your eyes, Science Alert reports.

The noxious, invasive weed was just identified in Clarke County, Virginia, near the Massey Herbarium at Virginia Tech. That brings the number of states it's been spotted in to 11, including Washington, Oregon, Illinois, Michigan, North Carolina, Pennsylvania, New York, Connecticut, Massachusetts, and Maine. Beyond the U.S., it has taken root all over the world, from the UK to Iceland to Australia.

Similar to the common but slightly less dangerous cow parsnip, giant hogweed is native to Central Asia and was first brought to North America in the early 1990s as an ornamental plant, its unique shape making it popular among gardeners. But it soon became invasive: Once it’s established in an area, it can take up to five years to eradicate a colony.

Now the plant is considered a public health concern. Hogweed can cause a reaction known as phytophotodermatitis when it comes into contact with skin that is subsequently exposed to UV rays—but the effects of hogweed are much more severe. A painful blister can develop within hours and last for months; the exposed skin can remain sensitive to sunlight for years even after the blisters heal.

Hogweed can be difficult to distinguish from the cow parsnip, and the plant is often misidentified. First, check for height: Hogweeds are typically taller than 8 feet, while cow parsnip tends to be 5 to 8 feet tall. Hogweed stems are green with purple specks and coarse white hairs, while parsnip stems are green with fine white hairs. For more tips and photos, check out the New York Department of Environmental Conservation’s guide.

If you see a plant you think might be a giant hogweed, take a few photos and send them to your state's department of agriculture to identify—and whatever you do, don't touch it.

[h/t Science Alert]