|Conium maculatum in California|
Conium maculatum, the hemlock or poison hemlock, is a highly poisonous biennial herbaceous flowering plant in the carrot family Apiaceae, native to Europe and North Africa. A hardy plant capable of living in a variety of environments, hemlock is widely naturalized in locations outside its native range, such as parts of North and South America, Australia and West Asia to which it has been introduced.
Conium maculatum is known by several common names. In addition to the British hemlock, the Australian carrot fern and the Irish devil's bread or devil's porridge, the following names are also used: poison parsley, spotted corobane, spotted hemlock, and poison hemlock. The dried stems are sometimes called kecksies or kex.
The plant should not be confused with the coniferous tree Tsuga, also known by the common name hemlock, even though the two plants are quite different. Similarly, the plant should not be confused with Cicuta (commonly known as water hemlock).
Conium maculatum is an herbaceous biennial flowering plant that grows to 1.5–2.5 m (5–8 ft) tall, with a smooth, green, hollow stem, usually spotted or streaked with red or purple on the lower half of the stem. All parts of the plant are hairless (glabrous); the leaves are two- to four-pinnate, finely divided and lacy, overall triangular in shape, up to 50 cm (20 in) long and 40 cm (16 in) broad. Although it looks like a carrot plant, poison hemlock can be distinguished by the smooth texture and light green color it possesses. The poison hemlock's flower is small and white. The flowers are loosely clustered and each flower has five petals.
It has been introduced and naturalised in many other areas, including Asia, North America, Australia and New Zealand. The plant is often found in poorly drained soil, particularly near streams, ditches and other watery surfaces. It also appears on roadsides, edges of cultivated fields and waste areas and is considered an invasive species in 12 U.S. states.
Conium maculatum grows in damp areas, but also on drier rough grassland, roadsides and disturbed ground. It is used as a food plant by the larvae of some Lepidoptera species, including silver-ground carpet. The poison hemlock moth (Agonopterix alstroemeriana) feeds on the plant during its larval stage. A. alstroemeriana has been widely used as a biological control agent for C. maculatum. 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.
The plant is poisonous to animals that graze on it. Studies have reported cases of intoxication in cattle, pigs, sheep, goats, donkeys, rabbits, and horses.
Conium and other alkaloid toxins
C. maculatum is known for its poisonous characteristic. Their tissues contain different amount of alkaloids. In flower buds, the major alkaloid found is γ-coniceine. However, this molecule is transformed into coniine later during the fruit development. The alkaloids are volatile; therefore, researchers assume that these alkaloids play an important role in attracting pollinators such as butterflies and bees.
Conium contains the piperidine alkaloids coniine, N-methylconiine, conhydrine, pseudoconhydrine and gamma-coniceine (or g-coniceïne), which is the precursor of the other hemlock alkaloids.
Coniine has a chemical structure and pharmacological properties similar to that of nicotine. Coniine acts directly on the central nervous system through inhibitory action on nicotinic acetylcholine receptors. In high enough concentrations, coniine can be dangerous to humans and livestock. With its high potency, the ingestion of seemingly small doses can easily result in respiratory collapse and death.
The alkaloid content found in C. maculatum also affects the thermoregulatory center by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves. In addition, alkaloid was also found to stimulate the sympathetic ganglia and reduce the influence of the parasympathetic ganglia in rats and rabbits, causing an increased heart rate. One of the reasons that poison hemlock is appealing to herbivores and animals, in general, is because of its appearance. Poison hemlock leaves look similar to those of carrots; therefore, animals often mistake this plant to carrots. Besides, due to its abundance, poison hemlock is more accessible to animals more than some edible plants. As a result, it is not surprising to observe poisonous cases caused by poison hemlock.
Coniine also has significant toxic effects on the kidneys. The presence of rhabdomyolysis and acute tubular necrosis has been shown in patients who died from hemlock poisoning. A fraction of these patients were also found to have acute renal failure. Coniine is toxic for the kidneys because it leads to the constriction of the urinary bladder sphincter and eventually the accumulation of urine.
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.
The onset of symptoms is similar to that caused by curare, with an ascending muscular paralysis leading to paralysis of the respiratory muscles, causing death from oxygen deprivation. 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 (0.1 gram) of coniine (about six to eight fresh leaves, or a smaller dose of the seeds or root) may be fatal.
It has been observed that poisoned animals tend to return to feed on the plant. Chronic toxicity affects only pregnant animals; when they are poisoned by C. maculatum during the fetus' organ-formation period, the offspring is born with malformations, mainly palatoschisis and multiple congenital contractures (arthrogryposis). Chronic toxicity is irreversible; though arthrogryposis may be surgically corrected in some cases, most of the malformed animals die. Such losses may be underestimated, at least in some regions, because of the difficulty in associating malformations with the much earlier maternal poisoning.
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. It is a common myth that C. maculatum alkaloids can enter the human food chain via milk and fowl, but scientific studies have disproven these claims.
Historical and cultural references
Conium maculatum is the plant that killed Theramenes, Socrates and Phocion. In ancient Greece, hemlock was used to poison condemned prisoners. Socrates, the most famous victim of hemlock poisoning, was accused of impiety and corrupting the young men of Athens in 399 BC, and his trial resulted in a death sentence. Although Socrates could have avoided death, he decided to take 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.
Socrates showed no fear drinking the poison given to him in a cup. He died after drinking it.
Although many have questioned whether this is a factual account,[who?] it is the perspective of Bloch that careful attention to Plato's words, modern and ancient medicine and other ancient Greek sources point to this account being consistent with Conium poisoning.
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|Wikisource has the text of the 1905 New International Encyclopedia article Hemlock.|
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