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In the roadsides and ditches of New York state lurks a plant straight out of your worst nightmare. It’s a relative of the carrot, but this carrot can grow to be over 4 meters tall, and if you’re not careful, it could send you to the hospital with third-degree burns.

Not only is it dangerous to humans, it’s also really good at crowding out native species. It’s called giant hogweed, and it’s one plant you don’t want to mess with. Giant hogweed is native to the Caucasus Mountains in western Asia.

It was introduced to Europe in the late nineteenth century and to the U. S. early in the twentieth century, because people thought it would look cool in their garden. It can get really tall, has leaf arrays that are up to 1.5 meters wide, and white flower heads that can be as big as three-quarters of a meter across, so yeah, I guess you could say it’s pretty remarkable looking.

But, inevitably, it busted out of people’s backyard garden plots and started to grow wild, usually along streams and roadsides. Today, it’s established in parts of Europe, southern Canada, and the US. It’s especially widespread in New York, but it’s been spotted in about a dozen states, including all the way across the country in rainy Washington.

What makes giant hogweed so dangerous is its sap, which can get on you if you break the stems or leaves, or even just brush up against the bristles on its stems. The sap contains organic compounds called furanocoumarins that can penetrate your skin cells, getting right up into the nuclei alongside the cells’ DNA. If these compounds are then hit by ultraviolet radiation, you know, like sunlight, they can absorb some of the light’s energy and trigger two of the nucleotides in DNA, thymine and cytosine, to form cross-links in your DNA strands that really shouldn’t be there.

Enough of these unwelcome disruptions, and the cells stop working. Hogweed’s relatives actually produce these nasty compounds, too, but usually at lower levels. Though people have reported burns similar to hogweed from contact with carrots, celery, or parsnips as well as some citrus fruits and figs that also make furanocoumarins.

And that’s because regardless of where they come from, you experience this DNA damage as a condition called phytophotodermatitis. That’s phyto, for plant, photo, for light, and dermatitis, for skin problem. In response to light, your skin turns red and can develop nasty blisters and burns, which can last for months.

You can also end up with dark patches because your skin tries to compensate for the light-induced damage by producing the pigment melanin to absorb some of the rays. Even after the initial burns heal, the affected skin can be sensitive to light for years. And if all that’s not awful enough, giant hogweed isn’t just bad news for us.

It can spell trouble for native plant communities, too. Each plant produces more than 20,000 seeds when it flowers, which it does just once. That’s a lot of potential baby hogweed plants.

As they grow, they can form tightly-packed stands. And once established, giant hogweed lives up to its name, hogging all the resources for itself. Its huge size and giant leaves allow it to shade out and eventually eliminate its neighbors.

And studies suggest it may even poison neighboring plants by sending toxins through the soil. If so, that means it engages in chemical warfare on multiple fronts, but the evidence is mixed. Given all this, it might be hard to understand why gardeners brought such a horrific plant around the world in the first place.

But not all non-native plants become giant hogweed-level menaces, so they probably didn’t see all this coming. Scientists are still figuring out why some non-native plants become invasive, meaning they cause serious harm ecologically, economically, or to human health, when others don’t. Giant hogweed has some characteristics that are often considered typical of aggressively invasive plant species, like it produces a lot of seeds and grows really fast.

But it lacks others, like that those seeds aren’t readily dispersed long distances by birds and such. Of course, no one plant has every characteristic that makes it a good invader, and multiple strategies can lead to success in a new ecosystem. So by studying species like giant hogweed, researchers can better predict what garden favorites will wreak havoc.

In the meantime, if you spot something you think might be giant hogweed, take some photos and send them to your local environmental authorities. In the US, many states have invasive species task forces for this kind of thing, or if nothing else, you can talk to someone at the nearest National or State Park or National. Wildlife Refuge.

And other countries usually have similar people you can inform. Whatever you do, don’t try to get rid of it yourself. Really.

Just don’t. Trust us. Thanks for watching this episode of SciShow!

If you want to learn more about some truly terrifying plants, you might like our episode on 10 plants that could kill you. [♪ OUTRO].