Poison Parsley

Poison parsley is another name for hemlock. Hemlock originally attained notoriety around 2500 years ago when it was used to poison the Ancient Greek philosopher, Socrates. He was executed because his teachings were highly critical of the Athenian state and he was a thorn in the side of various high ranking Athenians. And in those days that tended to limit ones life expectancy.

Hemlock – Conium maculatum

I hadn’t knowingly encountered hemlock until a couple of weekends ago when I was strolling around the RSPB reserve at Fen Drayton, where it was lining the hedgrows in some profusion. It is an imposing plant that was growing taller than me, up to around 2m, it has dark green feathery leaves and white flowers that resemble the hogweeds.


This plant was growing amongst hogweed and cow parsley, and it can appear fairly similar to both, to the uneducated eye.

A variable damselfy (Coenagrium pulchellum) warming itself in the early morning sunshine perched on a hemlock frond

The hogweeds used to provide fodder for pigs, hence the name, but giant hogweed is toxic to humans due to its sap which contains a type of chemical called a ‘furanocoumarin‘ that causes the skin to become sensitive to ultraviolet light. That can result in extremely unpleasant blistering of the skin and blindness if it gets in the eyes. Derivatives of furanocoumarins have been developed as drugs for the treatment of psoriasis.

But the hemlock toxin works in a different way. It is called ‘coniine‘ and the chemical name is 2-propylpiperidine:

I think this compound is remarkable because it is very small for a molecule which has such a specific and catastrophic effect. It exerts its effect by blocking a receptor for a neurotransmitter, acetylcholine, which resides on the membrane on the far side of nerve synapses. This results in a condition called ‘flaccid paralysis‘. Basically, the nerves which facilitate muscle contraction get blocked and stop firing. It starts in the feet and travels upwards, the muscles go floppy and that’s ultimately fatal when the effect reaches the heart and lungs. Socrates’ death was described by Plato and his last words were to his friend, Crito:

“Crito, we owe a rooster to Asclepius. Please, don’t forget to pay the debt.”

The smooth stem of the hemlock plant

The purple spots on the stem of the hemlock are diagnostic, other similar plants don’t have this, so if you see it, admire it, but don’t touch it! All parts of the plant are toxic and it doesn’t take much to have an effect.

The flower head just before the white flowers emerge

Hemlock has a number of names according the the Royal Horticultural Society: California fern, cashes, herb bennet, Nebraska fern, poison hemlock, St Benedict’s herb, snakeweed, spotted hemlock, spotted parsley and winter fern. Also according to the RHS, its range is Europe only, but it has been introduced to the United States, hence the two names which include U.S. states.

Hemlock grows in damp poorly drained soils and is fed on by various insects including caterpillars and occurs in field borders and roadside verges aswell as along the lakes and ditches where I found it at Fen Drayton.

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22 responses to “Poison Parsley

  1. I regularly deal with giant hogweed at work. Think I may have strimmed through some recently after getting some nasty blistering on my neck! Wasn’t aware of the effects of hemlock until reading this post, I will be looking out for this in my area…

    • That blistering sounds mighty unpleasant. I was warned not to go near giant hogweed when I was a kid but it was so uncommon it was’t a problem. But hemlock is fascinating stuff, look out the purple blotches on the smooth stem – they’re diagnostic for hemlock. It’s a splendid plant, especially when it’s at its maximum height.

  2. Fascinating post, Finn!

  3. We have a lot of hemlock around here. I didn’t know what it was until just recently when I went out with the San Diego Beginning Birders and one of our guides told us what the tall, beautiful plants were.

  4. We have hemlock growing as an alien species in Texas, including along the Colorado River that flows across the middle of Austin. Thanks for the explanation of why the plant is poisonous, even though the toxic molecule is so relatively simple.

    Steve Schwartzman
    http://portraitsofwildflowers.wordpress.com

  5. Delightful plant. Apparently in older legends, the purple streaks on the stem of water hemlock are the marks put on Cain’s brow when he murdered his brother!

    • Hello Theresa, it is an amazing plant and spectacular too, especially when there is a stand of it over 2m tall. Thanks for the legend too, I didn’t know that, and it’s a great story. I think legends like that are important because they reinforce the link between us humans and our surrounding nature.

  6. Luckuly we don’t have this, but there are some few in southern Norway..

  7. Pingback: Not in my back yard, thankfully | Back Yard Biology

  8. So very interesting. Thanks!

  9. I’m surprised to hear it called herb bennet, I thought that was a completely different plant, with little five-petalled yellow flowers (aka wood avens). Hemlock is a pretty nasty piece of work for rather an attractive plant, isn’t it? I wonder if I’ve been blithely enjoying what I thought was cow parsley when actually it was the killer, hemlock. I’ll have to check the stems more carefully from now on, just by eye of course. Your dragonfly photo is exquisite.

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