Of the vast menagerie of dangers in Yellowstone National Park, one of the most lethal appears as an innocent and potentially appetizing plant to the uninformed. But nobody should eat these “poisonous parsnips," which are considered the deadliest plant in North America.
Of 1,491 native plants in Yellowstone, only two are lethal enough to kill a human, even when ingested in small quantities. The deadlier of the two, at least in terms of confirmed human fatalities, is Cicuta maculata — spotted water hemlock.
You don’t have to go to Yellowstone to find this deadly plant. Any Wyomingite might find it innocuously growing in their neighborhood.
“I've seen it growing in alleys in Cheyenne and in places where kids or adults with bad information might pick it,” said Shane Smith, the former director of the Cheyenne Botanic Gardens. “We're surrounded by poisonous plants all over the natural world, but they don’t all look like something we're used to eating. That’s what makes water hemlock particularly scary.”
The Devil’s Parsley
Spotted water hemlock is deceptively dangerous because it’s a black sheep in a good family of well-known edible plants. It’s in the Apiaceae family, which includes savory root plants like carrots, celery, parsnips, and parsley.
That’s what Shane finds so frightening about spotted water hemlock. It can easily fool someone foraging for edible plants, as its succulent roots are very similar to wild carrots and parsnips, which also grow throughout Wyoming.
“People get a little bit of plant knowledge, and they think they know how to recognize parsley or carrots, and water hemlock is related to parsley and carrots,” he said. “They grab this stuff for salad and get incredibly sick.”
Ingestion of spotted water hemlock can cause abdominal pain, convulsions, delirium, nausea, seizures, and vomiting within an hour. Smith said it’s been known to cause respiratory failure in extreme cases and death in most cases.
“I had a friend who got a large blister just by touching it,” Shane said. “I’ve touched it before with no problem, so that side effect is not as ubiquitous among everyone, but I’d still put on gloves if I had to touch it.”
Even the stems of water hemlock, which vary in color from purple to green, are highly toxic. In his book, Whittlesey noted that there are documented cases of children fatally poisoned after using the hollow stems of water hemlock as whistles.
The poisonous compound contained in water hemlock is cicutoxin. It can be found throughout the plant but is most densely concentrated in the roots, adding to its lethality.
“Cicutoxin is a highly poisonous unsaturated alcohol that acts as a gamma-aminobutyric acid (GABA)antagonist in the central nervous system,” said Ted Smith, Horticulture Program Coordinator with the University of Wyoming Extension in Park County. “A GABA antagonist blocks or inhibits the action of the neurotransmitters in the brain, effectively reducing its inhibitory effects on neuronal activity.”
One mouthful of water hemlock root can kill an adult, and Shane said it would take only 100 grams of its leaves to kill a cow within 15 minutes. One of the plant’s many common names, including “Beaver poison” and “spotted parsley,” is “spotted cowbane.”
“It’s not something you want to mess around with,” he said.
Phillips Caldron
There’s an established tradition in Yellowstone: thermal features aren’t named after people. Phillips Caldron is an exception to that rule, named for the victim of the first confirmed death by water hemlock in the park.
Charles Phillips was a naturalist working in Yellowstone during the winter of 1927. On the night of April 11, he ate two raw water hemlock roots he had misidentified as roots of a different edible plant.
According to Lee Whittlesey’s book “Death in Yellowstone,” Phillips was found dead on the floor of his cabin near Old Faithful on the evening of April 12. Investigators said his body showed classic signs of hemlock poisoning and believed he died only a few hours after eating the roots.
Two other people, the Bauers, ate a small portion of the same hemlock roots eaten by Phillips. They were violently ill within a few hours of eating the roots but survived.
Phillips was a well-educated and well-liked figure in Yellowstone. Phillips Caldron, a thermal feature in the Norris Geyser Basin, was named in his honor.
This was the first of three possible deaths from water hemlock in Yellowstone, but the poisonous plant's lethal history goes back much further. In 399 A.D., Socrates, the famous Greek philosopher, was sentenced to death by drinking a cup of hemlock juice.
“There was an assisted suicide advocacy group called the Hemlock Society inspired by Socrates,” Shane said. “It was his choice to accept death (by consuming hemlock) rather than dying by another way. It's that easy to die from it.”
The Devil In The Details
Since spotted water hemlock is in the same family as carrots, celery, and parsnips, the plant looks superficially similar to them. Because of its white tuberous roots, it can easily be mistaken for wild parsnips – that’s the last mistake anyone wants to make.
Thankfully, Smith said spotted water hemlock has an obvious giveaway that tells everything to stay away - it’s in the name.
“It’s the small purple spots on the hollow stem,” he said. “We’re blessed with the fact that it has this distinctive trait. You don’t have to be much of a scientist to identify spotted water hemlock — it has its own warning label.”
Other traits that can be used to identify spotted water hemlock are the veins in the leaves that end in serrated notches and its white flower umbels. It tends to grow in wet areas like meadows, marshes, swamps, and the edges of ponds and ditches.
Ted said water hemlock can also be confused with Queen Anne’s lace, the edible “wild carrot.” Once again, the differences in their stems safely distinguish the two.
“Queen Anne’s lace has a hairy stem, which is green and can sometimes have a slightly purplish hue at the base, but lacks significant blotching,” he said. “The distinctive purple of reddish-brown blotches (on water hemlock) are a telltale sign of its toxic nature.”
Better-Off-Dead Bulb
The other deadly plant in Yellowstone National Park is Toxicoscordion venenosum, the meadow death camas. This bulb plant is common throughout western North America and is commonly mistaken for other edible plants like blue camas and wild onions.
“It can resemble a wild onion to untrained eyes,” Smith said. “If you squish the stem of a wild onion, it smells like an onion. If you squish the stem of a death camas, it smells like green stuff. But I wouldn't go squishing anything I'm not familiar with.”
Like the spotted water hemlock, the entire death camas plant is toxic. It contains zygacine, a neurotoxic alkaloid that can stay stable and lethal for up to two decades after being dried and stored. Even its nectar is toxic, leading to it being primarily pollinated by the death camas miner bee.
Symptoms of death camas poisoning include gastrointestinal issues, irregular heartbeat, difficulty breathing, and several others, with extreme cases resulting in a coma and possibly death.
Nevertheless, human poisonings from death camas are rare, and deaths are even rarer. There are no documented cases of either in Yellowstone, but Smith knows of at least one lethal case of death camas poisoning.
“I had a friend who was on a picnic in a park outside of Cheyenne with a guy who thought he knew a lot about wild plants,” he said. “He picked and ate death camas thinking it was wild onion, and died right then and there. He was trying to show off that he knew something about wild plants, and he didn't.
Perennial Poisonous Parsnip
Spotted water hemlock isn't the only water hemlock to look out for in Wyoming. Other species can also be found in certain sections of Yellowstone and Grand Teton National Parks.
Cicuta douglasii, western water hemlock, is more commonly found growing between the Rocky Mountains and the Pacific Ocean and from as far south as California to as far north as Alaska. Western water hemlock isn't as widespread as spotted water hemlock but can be found throughout western Wyoming.
"It's a little less distributed but equally poisonous," Shane said. "Thankfully, they have the spots on the stem, too."
Cicuta bulbifera, the bulblet-bearing water hemlock, is more common in the Pacific Northwest and Canada but has been found on the Yellowstone Plateau in the southernmost extent of Yellowstone.
Botanists might argue over the differences between these species and where they can or can't be found, but their lethality is beyond question. Someone could potentially find all three water hemlock species during a Yellowstone visit, and a small quantity of any of them is enough to kill if consumed.
Just don't go parsnip picking in Yellowstone.
Foraging Without Fear
One doesn’t have to go to Yellowstone to find spotted water hemlock. The plant is widespread throughout North America, including the lower 48 states and Alaska.
“It’s not very common as a whole (in Wyoming, but) it can be found in 15 counties and is a county-declared weed in Big Horn, Campbell, Lincoln, Platte, Sheridan, and Teton Counties,” Ted said.
Thankfully, even death by water hemlock can be prevented as long as anyone ingests it receives prompt medical treatment. It’s an increasingly rare cause of death in Wyoming, but that doesn’t negate its potency.
“A grizzly bear attack and death may be more common than death by water hemlock,” Ted said.
Shane said water hemlock and death camas are easy enough to avoid, but they can potentially be found growing anywhere in Wyoming. When it’s found, he recommends swift action.
“I would do everything I could to get rid of it every time you see it sprout up,” he said. “It could be germinating near your home right now, and it's just not something you want to have around.”
According to Shane, foraging for edible plants in Wyoming’s wilderness has come and gone as “a fad” over the decades. It can be safely done, provided the foragers are well-informed and don’t bite into anything unless they’re certain it’s safe.
“Foraging for edibles has been a thing for certain people,” he said. “You can come across wild strawberries and raspberries at higher altitudes, and that's a fun treat, but I’ve seen people walk down alleys and forage for edible plants. People just need to be careful.”
Shane recommended the books “Edible Native Plants of the Rocky Mountains” by H.D. Harrington and “A Guide to Rocky Mountain Plants” by Roger L. Willams, which are “great books” for Wyoming’s foragers, hikers, and outdoors enthusiasts.
Some plants can be processed to remove toxins and safely eaten and enjoyed. Spotted water hemlock – Yellowstone’s poisonous parsnips - is not one of them.
“There are several plants that fit that bill, but not this one,” Shane said.
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
