Updated 21 Jun 2012

Poison Hemlock

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Poison Hemlock

A large patch of Poison Hemlock (conium maculatum) turns up in a Bear Mead field.
Next week the grass is due to be cut for cattle feed. We must remove it by hand.....
See Wikipedia for more information about this very poisonous plant.

Poison Hemlock (conium maculatim).
3185. The tallest is 9 foot.
3188. Note the spotted stem.

Poisonous effect of Hemlock

Wikipedia says:
By far the more familiar species is Conium maculatum (Hemlock or Poison Hemlock). It is a herbaceous biennial plant which grows between 1.5–2.5 metres (5–8 ft) tall, with a smooth green stem, usually spotted or streaked with red or purple on the lower half of the stem. The leaves are finely divided and lacy, overall triangular in shape, up to 50 centimetres (20 in) long and 40 centimetres (16 in) broad. The flowers are small, white, clustered in umbels up to 10–15 centimetres (4–6 in) across. When crushed, the leaves and root emit a rank, unpleasant odour often compared to that of parsnips.

Conium maculatum grows in damp areas. It is used as a food plant by the larvae of some Lepidoptera species including Silver-ground Carpet. Poison hemlock flourishes in the spring, when most other forage is gone. All plant parts are poisonous but once the plant is dried, the poison is greatly reduced, although not gone completely.
Silver-ground Carpet
(Xanthorhoe montanata)

Conium contains the pyridine alkaloids coniine, N-methylconiine, conhydrine, pseudoconhydrine and ?-coniceine (or g-coniceďne), which is the precursor of the other hemlock alkaloids. The most important and toxic of these is coniine, which has a chemical structure similar to nicotine. Coniine is a neurotoxin, which disrupts the workings of the central nervous system and is toxic to humans and all classes of livestock. Ingestion in any quantity could result in respiratory collapse and death. Coniine causes death by blocking the neuromuscular junction in a manner similar to curare; this results in an ascending muscular paralysis with eventual paralysis of the respiratory muscles which results in death due to lack of oxygen to the heart and brain. Death can be prevented by artificial ventilation until the effects have worn off 48–72 hours later. For an adult the ingestion of more than 100 mg of coniine (approximately 6 to 8 fresh leaves, or a smaller dose of the seeds or root) may be fatal.

Effects on animals
C. maculatum is poisonous to animals. In a short time the alkaloids produce a potentially fatal neuromuscular blockage when the respiratory muscles are affected. Acute toxicity, if not lethal, may resolve in the spontaneous recovery of the affected animals provided further exposure is avoided. It has been observed that poisoned animals tend to return to feed on this plant. Chronic toxicity affects only pregnant animals. When they are poisoned by C. maculatum during the fetus's organ formation period, the offspring is born with malformations, mainly palatoschisis and multiple congenital contractures (MCC; frequently described as arthrogryposis). Chronic toxicity is irreversible and although MCC can be surgically corrected in some cases, most of the malformed animals are lost. Since no specific antidote is available, prevention is the only way to deal with the production losses caused by the plant. Control with herbicides and grazing with less susceptible animals (such as sheep) have been suggested. C. maculatum alkaloids can enter the human food chain via milk and fowl. Such losses may be underestimated, at least in some regions, because of the difficulty in associating malformations with the much earlier maternal poisoning.

In ancient Greece, hemlock was used to poison condemned prisoners. The most famous victim of hemlock poisoning is the philosopher Socrates. After being condemned to death for impiety in 399 BC, Socrates was given a potent infusion of the hemlock plant. Plato described Socrates' death in the Phaedo:
The man...laid his hands on him and after a while examined his feet and legs, then pinched his foot hard and asked if he felt it. He said "No"; then after that, his thighs; and passing upwards in this way he showed us that he was growing cold and rigid. And then again he touched him and said that when it reached his heart, he would be gone. The chill had now reached the region about the groin, and uncovering his face, which had been covered, he said – and these were his last words – "Crito, we owe a cock to Asclepius. Pay it and do not neglect it." "That," said Crito, "shall be done; but see if you have anything else to say." To this question he made no reply, but after a little while he moved; the attendant uncovered him; his eyes were fixed. And Crito when he saw it, closed his mouth and eyes.
Although many have questioned whether this is a factual account, careful attention to Plato's words, modern and ancient medicine, and other ancient Greek sources point to the above account being consistent with Conium poisoning.

Compiled, formatted, hyperlinked, encoded, and copyright © 2012, John Palmer, All Rights Reserved.