What Is Hemlock?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 04 July 2014
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The common name “hemlock” is used to refer to several different trees and plants with a number of different properties. Hemlocks can be found growing naturally in many regions of the world and some are deliberately cultivated as ornamental plants. Because of the fact that this common name is applied to a range of plants, botanists tend to use scientific names when talking about hemlocks to avoid confusion.

The parsley family, Apiaceae, contains several genera which are referred to as hemlocks including Conium, Cicuta,, and Oenanthe. All of these genera contain plants which are toxic, and the hemlocks look very similar to each other. Their foliage is similar to that of carrot greens, and their flowers grow in white umbrels. Many of the hemlocks are very open and branching, and can grow quite large. Some have stems speckled with purple.


Conium is probably the most famous genus because plants from this genus were once used for executions, perhaps most notably in Ancient Greece, where hemlock was provided to the philosopher Socrates when he was condemned to death. This genus is also sometimes referred to as posion parsley, spotted hemlock, or spotted corobane. The Cicuta genus or water hemlocks, also known by names such as cowbane or poison parsnip, is also highly toxic, and several of the Oenanthe species, known as water dropworts, are also poisonous. However, some are also used for food, making it especially important to be able to distinguish between different species in this genus to avoid gathering the wrong plant for the dinner table.

Poison hemlock is usually not ingested by humans because in regions where it grows wild, people who eat wild plants are familiar with the appearance and sharp scent of hemlock and know to avoid it. However, animals sometimes eat hemlock and they can become very sick. Repeated exposure to hemlock can lead to death in grazing animals like cattle and horses. For this reason, farmers inspect their fields for hemlock and other toxic plants before setting animals loose.

A completely unrelated genus, Tsuga, is also known as hemlock. The genus contains a number of species which are grown as ornamental trees. The “hemlock” name is used for these trees because they smell somewhat like the poisonous species discussed above. However, they are not toxic, and are perfectly safe to grow as ornamentals although they can tend to steal water from neighboring plants, so they should be positioned with care in the garden.


Discuss this Article

Post 8

What about if somebody (purposely or otherwise) ate Hemlock seeds? Would they die?

Post 7

Okay, people always talk about how to identify hemlock, and the steps go something like this:

Step one: What does it look like? If the leaves look like parsley and it has little white flowers, it's likely hemlock.

Step two: Where is it growing? Can't be hemlock if you're in a region where hemlock doesn't grow, right?

Step three: Here's the kicker -- what does the crushed plant smell like? If it smells like evergreens (stinky evergreens, as aishia notes, not the good-smelling kind) and matches the other stuff above, it's almost certainly hemlock.

Now about the smell part. It's possible to know all of this stuff and still get poisoned by hemlock if you're going on the smell part. See, every bit of a hemlock plant is poisonous, but hemlock seeds don't smell when you crush them -- only the stems and leaves and roots do.

So if you're testing the crushing part on the seeds, beware -- it could still be poisonous even if the smell part doesn't match up!

Post 6

@VivAnne - I agree entirely. Somebody should start up a movement to switch misused words to their rightful usages again, and quitting calling the Tsuga tree a hemlock should be on the list.

The smell of crushed hemlock is actually pretty gross -- it smells like parsnips, kind of pungent and rank. Since the Tsuga is an evergreen, I'll bet it might smell similar to hemlock, but still smells better. Evergreen trees tend to smell nice, like Christmas tree clippings do.

Whoever started calling the Tsuga tree a hemlock, they really should have figured that calling the tree the exact same name as the weed hemlock would confuse people. Instead, maybe they ought to have name the tree the "Hemlock Tree" to emphasize that it was similar to hemlock but not the same, or something like that.

Though they're actually not related in the least, so really the person ought to have just left well enough alone... People don't expect things like nicknames to catch on sometimes, though, i guess.

Post 5

@ahain - Very interesting -- I wonder if the same treatment that is applied to Conium hemlock poisoning could be applied to mushroom neurotoxin poisoning? Perhaps not; I don't think all neurotoxins paralyze in such a neat and tidy sequence from the feet upward.

As with many neurotoxins from the world's most poisonous creatures and plants, Conium's coniine poison has been used over the centuries for medicinal purposes as well as the more grim task of executions.

A tiny bit of a neurotoxin can temporarily numb pain and calm spasming muscles without causing any permanent damage. As ahain pointed out in their post, even a full fatal dose of Conium hemlock doesn't cause damage, it just paralyzes the body so much that it damages itself because it can't get oxygen. Used in controlled doses, it can be helpful to ease suffering.

Coniine was sometimes used by the ancient Persians and Greeks to treat arthritis, among other ailments. Because the numbing effect has an antispasmodic property, it has been used medicinally as a sort of tranquilizer, too.

It was a risky business in the stage of medical technology they had back then, though, because just a bit too much of a dose would go from helpful to fatally paralyzing. Overdosed patients would lose the ability to speak or move, followed quickly by lung paralysis and death due to oxygen deprivation.

Post 4

@Mor - The kind of hemlock that killed Socrates, which is referred to by the scientific name Conium by professionals to avoid confusion with other hemlock types, kills in much the same way as a poisonous mushroom: neurotoxin.

The neurotoxin that Conium hemlock creates is called coniine. The toxin itself isn't what causes the death, but the side effects of it are.

Coniine neurotoxin paralyzes the body in the peculiar sequence you described from Socrates' death -- from the feet upward. When it reaches around the chest area, the lungs become paralyzed, resulting in a complete cut-off of oxygen to the brain and heart.

That means that it's not damage, just paralysis of important organs, that causes death by Conium poisoning -- and that means that today, Conium poisoning is not fatal so long as the person receives proper medical attention in time.

If someone with Conium poisoning is hooked to life support equipment that artificially moves their lungs for them for two or three days until the toxins wear off, the heart and brain never suffer oxygen deprivation, and so the person can walk away from a fatal poisoning, alive and well.

Post 3

@pastanaga - I always thought of hemlock as a tree, too -- everybody who ever used the word around me was referring to an evergreen tree with cones. This perplexed me so much that I went and looked it up, and lo and behold, there is in fact a tree referred to as a hemlock as well as the Conium hemlock parsley-like one.

The article mentions these trees briefly as being called the Tsuga, but doesn't explain what they look like, so I'll elaborate here for anybody else who, like me, was curious if it was the tree they always imagined hemlocks to be.

The Tsuga tree is a species of evergreen pine tree that grows cones, so it's a conifer, too. It can grow really big -- up to nearly 60 meters tall! The pine cones it makes are pretty big, too, and when the limbs grow out to their full length, the tips tend to droop because they aren't perfectly stiff.

The Tsuga matches exactly what I've always thought a hemlock is, but as the article notes, it's only even called "hemlock" because the smell of its crushed leaves reminded somebody of the smell of actual hemlock. Whoever mentioned it must have gotten a lot of agreement, because everybody else started calling the Tsuga a hemlock, too.

Now that I know what a real hemlock plant is, I'm going to stop carrying on the chain of misunderstanding, here -- I'll call the Tsuga a pine tree called "Tsuga". That's pronounced the Japanese way, for the record: "SUE-gah".

Post 2

I always thought hemlock was a tree, but it's a plant that is about the same size as ragwort. You need to really make sure that there is none in your fields if you are putting animals out. Cows especially, because sheep are less likely to eat it.

The poison in the hemlock plant might have a drug like effect, because apparently if you have a cow that eats some and recovers, they are more likely to try it again.

I can't imagine why they would do that unless it was addictive in some way, because usually animals and people associate getting sick with the thing that got them sick and avoid it after they get better.

Post 1

The most interesting thing about Socrates being given hemlock was that he was given the chance to run away, and he refused.

He absolutely believed that people should obey the law, and even though he was accused of very vague charges (like corrupting the youth), when he was sentenced to death he accepted it.

He apparently drank the hemlock potion without resisting and described the sensations to one of his friends who was standing nearby. It felt like his body was slowing going numb, bit by bit.

I can't even imagine how awful his friend must have felt, having to watch someone he cared about die like that.

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