Poisonous plants like poison ivy and giant hogweed can cause irritation, pain and scarring, but there are other plants — wicked plants — that are downright deadly. Joining me this week to discuss the stories behind the world’s most dangerous plants is New York Times bestselling author Amy Stewart.
Amy lives in Portland, Oregon, where she writes nonfiction books about the natural world, including “Wicked Bugs,” “Gilding the Lily,” “The Drunken Botanist” and the subject of this week’s conversation, “Wicked Plants.” Amy also writes historical nonfiction, and her 14 books in all have sold over a million copies worldwide and have been translated into 18 languages.
“Wicked Plants” has an attention-grabbing subtitle: “The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities.” It features nearly 40 plants with sordid histories. Amy explains that the idea for “Wicked Plants” grew out of her research for a book she wrote on the global flower industry.
“I was going around in greenhouses and talking to botanists and horticulturists,” she says. “… I’d walk into somebody’s greenhouse and they would say, ‘Hey, before you leave, come over here and let me show you this thing I have growing in the corner. Now I don’t want my boss to know I have one of these, but …’”
She says it would often be a plant that is creepy, weird, poisonous, dangerous, illegal and horrifying.
“Wow, you really go over to the dark side after a while when you’ve lived with plants long enough,” she recalls thinking.
Rather than writing a guide to poisonous plants — several already existed — she was interested in writing about wicked plants’ intriguing stories.
“I just got to be very selective and only pick plants that had really interesting stories,” she explains. “Like, I didn’t care that it could kill somebody. I just wanted to know who it had killed, and so it ends up being this quirky little weird book that’s not at all comprehensive, but that’s purely entertaining.”
When she was working on the book in 2007 and 2008, she would go on Wikipedia and look up plants. “Anything that was on Wikipedia was what I didn’t want to say,” she notes. She wanted to write the stories that no one knew about. “Where can I go outside of the plant world to find stories about these plants?” she wondered.
Amy looked through 200-year-old medical journals and read obituaries in old newspapers to uncover stories that had been lost to history.
“Plants have their defense mechanisms to keep from getting eaten,” Amy points out. “Most of the plants that you encounter all day, every day, are not breakfast food for you. They are not salad ingredients. They’re not for you. They’re not about you. … If something’s green and growing in the ground, we tend to think that it’s for us and that it’s all organic and it’s plant-based, and it’s all natural. And we’ll just pop it in our mouths — and that’s a terrible idea. The plant kingdom makes some of the most deadly poisons in the world.”
Amy encourages us to have a healthy respect for plants the same way we do for other elements of nature, like wild animals or the ocean. “Plants are very powerful, and we got to respect that power and not take it for granted,” she says.
Chelsea Physic Garden
The Chelsea Physic Garden is a botanical garden in London originally founded in 1673 by the Worshipful Society of Apothecaries as the Apothecaries’ Garden. It was intended to grow plants to be used as medicines.
I made it to London for the first time a couple of years ago and visited the Chelsea Physic Garden after the annual Chelsea Flower Show. Had I read “Wicked Plants” before visiting Chelsea Physic Garden, I would have appreciated it even more.
Amy says plants are living green chemical factories. They make these chemicals for their own purposes. “They’re not thinking about us. They’re doing it for themselves,” she says.
Plants may produce chemicals to defend themselves against predators or to attract pollinators, among other reasons.
“Some of those chemicals happen to be really useful as medicines,” Amy says, though she points out that, like many medicines, they are helpful in the right dose and dangerous in the wrong dose. “There’s a very thin line between medicine and poison.”
People living in London hundreds of years ago would go to an apothecary when sick, and all the apothecary had to offer to soothe symptoms was plants, maybe dried up or soaked in alcohol to extract the chemicals and keep them shelf stable.
“You had these pharmacists who were just handing out plants to people and hoping that would work, and usually it didn’t,” Amy says.
Sometimes, the plants did work, so keeping them on hand was a priority.
“The Chelsea Physic Garden was a place where those plants could be grown and where pharmacists could look at them and identify them,” Amy explains. Back then the next best thing to seeing an actual plant was a drawing or a woodcut of that plant in a book — and books were not easy to get your hands on.
“Being able to see the real plant was extraordinarily useful for those folks, and they also kept a garden of poisonous plants,” she says, explaining that by keeping poisonous plants around to familiarize themselves with, they knew which plants to never give out.
“The Chelsea Physic Garden is still there today, and all of those things still exist inside that garden. So it is this amazing experience of time travel to go to the Chelsea Physic Garden. It also really makes me appreciate the drugstore down the street. It’s like, ‘Thank you, Walgreens. I probably don’t say it often enough. Super glad you’re there.’”
The Chelsea Physic Garden in London, England.
(Photo Credit: Joe Lamp’l)
Rosary Pea
The plant in Amy’s book that hits closest to home for me is the rosary pea (Abrus precatorius). This plant is very common in the tropics, and it is also found where I grew up, in Miami. This vine and its pods were everywhere. The peas themselves are bright cherry red with black tips — very intriguing to a child. I can’t believe my mother didn’t go and hack every rosary pea down within a block. But I must have never eaten one because here I am today to talk about them.
“I love this one because I love what they look like,” Amy says. “They’re very satisfying little creatures. These seeds, they’re quite hard and round and smooth. And they kind of remind me of little ladybugs. They’re about the size and color of a ladybug with just one black spot.”
The toxin that comes from Abrus precatorius is called abrin, and it has been used in international terrorism incidents before. “It is known as one of the most toxic plants in the world in terms of how much it would take to kill a person,”
Amy notes.
The peas are used for beads in jewelry-making
“You punch a hole in it and run a string through it, and you can make a very charming necklace, but punching that hole in it makes it easier for the poison to get into your digestive system,” Amy says.
A rosary pea copper etching by Briony Morrow-Cribbs for the book “Wicked Plants” by Amy Stewart.
Castor Bean
The poisonous plant that Amy desired to grow more than any other is the castor bean (Ricinus communis). It is a gorgeous plant with dark red leaves and flower spikes. I see it every time I visit the Georgia Botanical Garden in Athens, Georgia, and I think to myself, “If people only knew.”
The beans contain ricin.
“It would only take a few of those seeds, if they were chewed really well, to kill a person,” Amy says. “… Ricin got kind of famous in the ’70s when there was a Russian dissident named Georgi Markov who was assassinated by the KGB. He was in London and after he died, at the hospital, they found a little pellet in his leg that contained ricin.”
The pellet was shot into his leg by a modified umbrella.
No one knew then precisely how much ricin it takes to kill a person. An experiment was done on a pig that weighed the same as Markov to determine how much ricin it took to be lethal to him.
“You don’t have to run screaming away from [castor bean]. Just don’t eat it,” Amy advises.
For people concerned about their toddlers or pets eating the beans, the plants can be cut back before they go to seed.
The Brooklyn Botanic Garden hosted an exhibit about “Wicked Plants” when the book came out in 2009. “They had a lot of castor bean, and they were telling me that after 9/11, the newly formed Department of Homeland Security came around wanting to see their castor beans and wanting to document where those plants were.”
The Department of Homeland Security wanted to know where those plants were because they were a potential bioterrorism agent. The Brooklyn Botanic Garden employees had to explain to them that castor bean is for sale at garden centers everywhere and can be bought from a seed catalog.
“It’s this disconnect between how the horticulture world works and how counterterrorism works,” Amy says.
Castor bean is an attractive plant but also the source of the poison ricin. (Credit: Copper etching by Briony Morrow-Cribbs)
Monkshood
To promote the Brooklyn Botanic Gardens exhibition, Time Out New York asked Amy to write a piece on “How to Murder Your Dinner Guest.” Amy picked monkshood (Aconitum) as the right plant for such a task.
Monkshood has a taproot that resembles a parsnip or carrot. “If you weren’t looking too closely, you might make a mistake along those lines,” she says. And in her research, she found that it has actually been used to kill people at a dinner.
Hemlock
Hemlock (Conium maculatum) is the plant that was used to kill Greek philosopher Socrates in an act of capital punishment for the crime of impiety.
Hemlock is in the carrot family and looks similar to Queen Anne’s lace, only it has purple spots on the stems.
“After the book came out, I got a call from a guy who had been poisoned by hemlock, and it was so fascinating to me to get to talk to someone who’d been through it,” Amy shares.
He was growing carrots in his backyard, in the Pacific Northwest, and hemlock turned up as a weed among his carrots. He harvested some carrots to make kimchi, and he didn’t pause when some of the “carrots” he harvested came up white.
He ate a little kimchi and then got in his car to drive to a friend’s house. On the way, he noticed that his peripheral vision didn’t work. He could not move his eyes from side to side. That was the beginning of the paralysis that sets in with hemlock poison, Amy explains. It paralyzes from top to bottom.
“He was able to get right to an emergency room, but he also had the presence of mind to call a poison control center,” Amy says. “… So they were able to quickly troubleshoot, ask him the right questions, narrow it down, hit on this possibility, and they called ahead to the emergency room and said, ‘He’s coming. We suspect hemlock poisoning. Here’s what you want to look for. Here’s what you want to test for.’”
In addition to the poison control centers for people, there’s a poison control center specifically for pets sponsored by the ASPCA.
Hemlock is in the carrot family and looks similar to Queen Anne’s lace, only it has purple spots on the stems.
(Photo Credit: Amy Prentice)
Sago Palm
Sago palm (Cycas revoluta) is a cycad houseplant that can also be grown outdoors in warm climates. Dogs may chew on them or eat a leaf that has dropped off.
“It’s very toxic to dogs, and unfortunately, after the book came out, I have heard from so many people whose dogs were poisoned by sago palm,” Amy says.
Plants don’t come with warning labels, so if you have a pet who gets into anything, research plants before you bring them into your home or grow them in your yard.
Sago palm is a cycad houseplant that is very toxic to dogs. (Credit: Copper etching by Briony Morrow-Cribbs)
Lilies
The lilies (LilIum) growing in your garden or displayed in a vase in your home are poisonous to cats. They can cause kidney failure in cats, and there is not much that can be done about it, Amy says.
Lilies are poisonous to cats, leading to kidney failure.
Oleander
Oleander (Nerium oleander) is a ubiquitous Southern shrub or small tree. It contains cardiac glycosides that can stop the heart. The flowers are candy-colored, red and pink, making them attractive to toddlers.
Amy adds that when poisonous plants are added to compost, the poisons that remain in the composted organic material cannot transfer to other plants, like tomatoes, so using the compost in an edible garden is not a concern.
Oleander contains cardiac glycosides that can stop the heart. (Credit: Copper etching by Briony Morrow-Cribbs)
Jimsonweed
Jimsonweed (Datura stramonium) is a nightshade with trumpet-shaped flowers. It is also known as devil’s trumpet.
“You can buy them at the garden center. They’re beautiful in containers. I love them,” Amy says. However, she adds that they can interfere with heart rate and breathing and cause a lot of dizziness. At high levels, the poison can cause hallucinations and can kill.
“And one of the interesting things about Datura is you can get a little of the poison through your skin,” she noted.
If kids just roll around in jimsonwood, they can get poisoned. The symptoms to watch out for, Amy says, are a red and flushed face, babbling, not making any sense, and having trouble breathing.
Mala Mujer
Amy shares a story of a young woman who went for a hike and came back with a rash on her back in the shape of a handprint. How could this happen? Amy surmises that the woman’s boyfriend had handled maja mujer during the hike, then put his hand on her back.
Mala mujer (Cnidoscolus) grows in Mexico and in the Southwest United States. It has a phototoxic, very irritating sap.
Blue-Green Algae
Blue-green algae, also known as cyanobacteria, is not actually a plant and not even an algae. It is a toxic bacteria, but it made the cut for “Wicked Plants” anyway.
Cyanobacteria can build up in our waterways, leading to toxic algae blooms and warnings not to swim in the water or let kids or pets near it.
In the early 1960s, in Santas Cruz, California, people woke up in the middle of the night to the sound of seagulls crashing into houses and cars. People went outside with flashlights to see what was going on, and the flashlights disoriented the birds, causing them to fly into people. What caused this phenomenon? An outbreak of toxic blue-green algae was occurring in Monterey Bay. The fish ate the algae and the fish got sick, and then the birds ate the fish. and the birds got sick.
“They kind of all came crashing down to the ground all at once as a result of this poisoning,” Amy explains,
When filmmaker Alfred Hitchcock wondered how he could adapt Daphne du Maurier’s short story “The Birds” into a movie, he took inspiration from the accounts of the seagull event.
Ergot
Ergot (Claviceps purpurea) is a fungus that grows on cereal crops like rye and other grains.
“Ergot contains precursors to LSD,” Amy says. “… You can get crazy and very unpleasant, frightening hallucinations from consuming rye grains that have been infested with ergot. And the really tricky thing about this is that it survives the process of being baked into bread or brewed into beer. So, going back, at least as far as the Middle Ages, we have records of these outbreaks happening sometimes in a little village. The whole village kind of goes crazy all at once.”
Ergot can also explain the Salem witch trials. Girls went crazy all at once, and their behavior was attributed to them being bewitched.
“If you look back, it turns out that the conditions were right for ergot poisoning that year. It had been a very wet winter and so forth. It kind of could have been a year for that, and while Europeans were starting to figure out that all you gotta do is rinse the grains with a saltwater solution, and that knocks it out. They didn’t know that yet in the Americas.”
Rye infected with ergot. Ergot is a fungus that grows on cereal crops. (Credit: Copper etching by Briony Morrow-Cribbs)
Deadly Nightshade
The nightshade family (Solanaceae) includes crops we eat such as tomatoes, peppers and eggplants but also tobacco and deadly nightshade (Atropa belladonna).
Deadly nightshade is a low-growing herbaceous plant with little purple berries. Amy found a medical journal article about an elderly woman who would go on a walk every day and pop little berries off a shrub and eat them. She got more and more delirious, which was attributed to her age, but the delirium was seasonal. She was only ill in late summer or fall when the deadly nightshade was fruiting.
Deadly nightshade can cause a wide range of symptoms and, when consumed in a great enough quantity, death.
The plant was also used by women to dilate their pupils as a beauty technique, but this could lead to blindness.
Deadly nightshade may look like an edible fruit but is poisonous. (Credit: Copper etching by Briony Morrow-Cribbs)
Elderberry
Before they are ripe, the fruit of elderberry (Sambucus) contains some cyanide. This is to deter birds from eating the berries before they are ripe and the seeds are mature. The cyanide level goes down when the berries are fully ripe.
“People will make elderberry wine, but you should not drink raw unprocessed elderberry juice because there could still be enough cyanide in there to cause you problems,” Amy says. “But the process of making it into wine or jam or something like that, you lose the cyanide at that point.”
Angel’s Trumpet
Also in the nightshade family is angel’s trumpet (Brugmansia). Amy has an acquaintance who pruned angel’s trumpet with her bare hands and then rubbed her eye. This caused her pupil to dilate. She went to the emergency room, where the doctors determined she had gardener’s mydriasis, or gardener’s pupil.
Brugmansia, Datura and other plants that contain atropine can all cause gardener’s mydriasis when handled improperly.
The Stinging Tree
In Australia, there is a plant found in rainforest areas known as the stinging tree (Dendrocnide moroides).
“The most painful plant in the world is this giant stinging tree in southern Australia, which looks like peach fuzz on the leaves,” Amy says. “They’re these tiny little needles — they’re called trichomes — so small that you can barely see them. But every one contains a very tiny dose of a potent neurotoxin.”
The trichomes get under the skin very easily if touched. Sometimes, they’ll break off and float around in the wind, and in the right conditions, you could accidentally breathe some in or get them in your eyes or your mouth, Amy says. “And it’s said to be the worst pain that a plant can inflict. And if you really got thrown into one of these bushes and got it all over you, it can be such a shocking amount of pain that people have had heart attacks from just the pain. And the pain can last up to a year, and it can be reactivated by heat or sunlight or cold.”
A hair removal strip can get the tricomes out of the skin — but it’s so painful, take a shot of whiskey first, Amy advises.
Stinging tree is found in the rainforests of Australia. Its trichomes get under the skin very easily if touched. (Credit: Copper etching by Briony Morrow-Cribbs)
Snakeroot
When grazing cows eat snakeroot (Ageratina), not only do the cows get sick, but anyone who drinks their milk also gets sick, perhaps fatally.
“This was called milk sickness, and no one knew what caused it for a long time,” Amy says.
Abraham Lincoln’s mother, Nancy Hanks Lincoln, died of milk sickness when Lincoln was only 9 years old, along with his aunt and uncle.
“So people knew that milk sometimes could make you very sick, but people were living off the land. They kind of had to eat and drink what they had, and it didn’t happen all the time,” Amy says.
When some parts of the country learned what caused milk sickness before others, the U.S. Department of Agriculture spread the word via the Farmers’ Bulletin. “That was how news got out to farmers about how to grow food safely and economically, and it was sort of like the social media of the day,” Amy says.
“These plants are fascinating,” Amy says. “I enjoyed growing them. I had a little poison garden for a while at my house, which was a lot of fun because some of these plants are hard to come by.”
She made a spooky goth garden with tombstones and skeletons. “I had a lot of fun with it, but it was not super practical because, you know, how many people are you really gonna poison? Probably not too many.”
She has since replaced it with a cocktail garden.
I hope you enjoyed my conversation with Amy Stewart on wicked plants. If you haven’t listened to the podcast yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you have an experience with wicked plants? Let us know how in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 120: Poison Ivy: What You Need to Know to Minimize Its Impact on You and Your Landscape
Episode 382: The Tree Collectors: Amy Stewart’s Tales of Arboreal Obsessions
Amy Stewart on Instagram | @amystewart
Amy Stewart on X | @amy_stewart
“The Tree Collectors: Tales of Arboreal Obsession” by Amy Stewart
“The Drunken Botanist: The Plants that Create the World’s Great Drinks” by Amy Stewart
“Wicked Plants: The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities” by Amy Stewart
“Wicked Bugs: The Louse That Conquered Napoleon’s Army & Other Diabolical Insects” by Amy Stewart
“Gilding the Lily” by Amy Stewart
“Flower Confidential: The Good, the Bad, and the Beautiful in the Business of Flowers” by Amy Stewart
“The Earth Moved: On the Remarkable Achievements of Earthworms” by Amy Stewart
“From the Ground Up: The Story of a First Garden” by Amy Stewart
“Taming the Garden” film trailer
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