AO Wants to Know is an ongoing interview series where we ask experts in extraordinary subjects to share their knowledge with us.
The inability to notice plants as living parts of the environment is an unfortunately common state of mind that botanists call “plant blindness.” “People just see plants as green,” says plant toxicologist Liz Dauncey. In their minds, plants “don’t do anything. They just sit around. They’re boring.”
Dauncey considers part of her work to be “chipping away at that plant blindness one person at a time.” For botanists, plants are not just a backdrop: They’re every bit as engaging and exciting as animals. Like animals, plants are locked in a constant battle to survive and reproduce. And like animals, some plants are armed with formidable defenses. This doesn’t mean we can’t appreciate them, but it may require some extra caution, thanks to what Dauncey calls an “absolutely remarkable set of compounds”: plant toxins.
Dauncey’s work on poisonous plants began in 1992, when she was enlisted by the Royal Botanic Gardens, Kew, in London and the local branch of the U.K.’s National Poisons Information Service to help develop a manual for poisoning treatment centers. In the 1990s, Dauncey explains, “We didn’t have the internet like we do now. People were reliant on a few books that they might have in the hospital. You couldn’t just Google a plant image or something and get an identification. So we were trying to fill a gap.”
From there, Dauncey got involved in other projects to help reduce poisoning incidents and keep people informed. Another information gap was a lack of warnings for toxic garden plants. “If you bought bleach, for example, it would have a warning on it,” says Dauncey. “But you could go into a garden center and pick up a quite poisonous plant, and not have any warning.” With the U.K. Horticultural Trades Association, she helped develop a downloadable system of warning labels, now in widespread use. Dauncey has also authored books including Plants That Kill, a guide to the world’s deadliest flora, with coauthor Sonny Larsson in 2018.
Dauncey spoke with Atlas Obscura about her work on improving public safety knowledge and what people ought to realize about poisonous plants.
What are some of the most common ways that plant poisons work?
They quite often affect your gastrointestinal system. Initially, they’ll make you sick. There’ll be nausea, vomiting, pain, and diarrhea, because your body will just try and get rid of it as quickly as it can. If it gets into the bloodstream, then it can affect the heart, either speed it up, slow it down, or make it become irregular. A lot of things affect the nervous system. They can give you seizures or paralysis, or bring on confusion or visual hallucinations.
Cyanide affects every cell in your body that it comes into contact with, such as in the digestive system. It stops the mitochondria from working, so you no longer have oxygen available in your cell. [Where toxins are] destroying the liver cells or the kidneys, those tend to be the long-acting things; you need multiple exposures for those.
This is probably hard to quantify, but, is there a plant that is considered the most poisonous?
That’s an intellectual rabbit hole! I know some people will answer that, but I would say it really depends on so many factors. If you want speed of death [as a factor], that just depends on the amount that you take. We all know from the whodunits that cyanide can kill you quite quickly. And all the things that we use as arrow poisons [Strychnos and Strophanthus species, and many more], they kill pretty quickly, because you’re getting it directly into the bloodstream.
There are a lot of plants that are much more poisonous if they’re injected directly into the bloodstream than if they’re eaten. Castor beans—if you chew them, you can be poisoned, but it’s very rarely fatal, especially if you get treatment. If you inject [the toxin] into the bloodstream, it’s not good. But that’s such an unusual route of exposure.
What are some of the most dangerous plants that people regularly come in contact with?
In the U.K., the most common is probably foxglove. It’s in a lot of people’s gardens. And we’ve got quite a few [toxic] houseplants in the arum family [Araceae] that you might know, such as dumb cane (Dieffenbachia), peace lily (Spathiphyllum), and Alocasia or Colocasia [elephant ear]. People might not realize that the sap from Euphorbias is potentially quite caustic. It’s a chemical irritant, and it’s particularly nasty if you get the sap in your eyes.
They’re the most common in the garden and house, but around the world, it will vary. In warmer countries, they’ll be growing oleanders and things like that.
What do regulations around poisonous plants look like in the U.K.? Is there a point at which a plant is considered too dangerous to be sold as a garden plant?
The only plants they regulate are the potentially invasive ones, and that’s quite a small list. The only way that poisonous plants are regulated in the U.K. is if you want to use them medicinally. Our Medicines and Healthcare Products Regulatory Agency has got a list of plants that can only be dispensed by a qualified pharmacist. But you can grow anything, except for a few not allowed ones, like cannabis or coca. You can grow opium poppy, but you could be prosecuted for extracting the latex [juice].
Besides ingestion of the plant, what are some ways that plants can poison people that might be less obvious?
I mentioned skin, the chemical irritants, but there’s also phototoxic reactions. If you get the sap of giant hogweed on your skin, and you expose the skin to bright UV light, you get blistering, which can last for a couple of weeks. And that patch of skin can be sensitive to sunlight for six months or more.
But I suppose the oddest and most unusual way is inhalation. There is a published case report of a family in India that was poisoned by inhaling smoke from burning oleander in an open fire in their dwelling. The mother was the most seriously affected because she was tending the fire and cooking, but it produced the cardiac symptoms that you would expect from ingesting oleander [an irregular heartbeat]. And in the U.K., we’ve had a couple of anecdotal reports of inhalation of cyanide from people who have pruned a cherry laurel hedge. If you take the prunings into your garage and shred them, and you’re in a confined space, it releases cyanide. But the gas has to be concentrated for that route of exposure.
There was a case where [the person] had bagged up their cherry laurel clippings and popped them into the car, and then they’d gone and had a cup of tea or something. And when they were driving to dispose of the clippings at the local council site, they became dizzy. It was [only] a mild poisoning, but an unusual route.
What should a person do if they suspect that they’ve been poisoned by a plant?
If you have come into contact with a potentially harmful plant, you should wash the area immediately with warm, soapy water and keep it out of direct sunlight. And if you think you’ve ingested something poisonous, don’t make yourself sick. You can have a little drink of water or even milk, or if you’ve got an irritated throat, you can have a little bit of vanilla ice cream. And then, if you are [still] concerned, seek medical attention.
Are there a lot of common misconceptions about poisonous plants?
I don’t like to generalize about what people think, but the media has certain misconceptions, and perhaps people get their information from there. When people overestimate the toxicity of something, it’s almost like the plant is a problem just for existing. They forget that in order to be poisoned, you have to interact in some way.
If I look at a specific case, about 10 years or so ago, there was a gardener who died, unfortunately. His family went around the garden that he’d been working in, and there was Aconitum growing there. Aconitum is monkshood or wolfsbane. They looked it up and found that Aconitum was poisonous, and that was put forward as a cause of death.
With the inquest [for the death], it was shown that it was highly unlikely that it was the Aconitum. The man had hardly touched it that day, and it’s not poisonous to that degree. But people still think that Aconitum is very poisonous if you touch it. If you strip the leaves, you can absorb enough toxin through your hands to be dizzy, you may get palpitations; but that’s it, and that is someone who’s handling it a lot. I garden with Aconitum, and it’s not a problem. The simple rule is, if you’re going to be handling a lot of plant material and getting sap on your hands, wear gloves, and then it’s perfectly fine.
Why do some poisonous plants become really infamous for being dangerous, while others remain under the radar?
I think it’s because of the stories that go along with them that a few of these plants become notorious. People would have got it in the past from say, Shakespeare; he had a lot of plants in his plays. And I’m sure Homer did as well. Nowadays people get the stories from things like Harry Potter. He’s introduced people to wolfsbane and mandrake. Teen Wolf also had wolfsbane featured in it quite prominently. I have to say that they were using a yellow Delphinium sometimes, and not a wolfsbane, but, you know, that’s a hazard of being a botanist watching these things.
This interview has been edited and condensed for length and clarity.
