Conium maculatum

Hemlock can grow to a height of 1.5 to 3 meters.

Conium maculatum is a 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.[2] Hemlock's flower is small and white; they are loosely clustered and each flower has five petals.[3] The plant looks like the wild carrot plant (Daucus carota). One can distinguish the two from each other by hemlock's smooth texture, mid-green, quite vivid, color and typical height of large clumps being least 1.5 metres, twice the maximum of wild carrot. Carrots have hairy stems that lack the purple blotches.[4] It can be confused with harmless cow parsley (Anthriscus sylvestris).

The hemlock plant is native to Europe and the Mediterranean region.[5]

It exists in some woodland (and elsewhere) in most British Isles counties;[6] in Ulster these are particularly Down, Antrim and Londonderry.[7]

It has become naturalised in Asia, North America, Australia and New Zealand.[8][9][10] It is introduced in 12 U.S. states.[11] It is sometimes encountered around rivers in southeast Australia and Tasmania.

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[8] Conium maculatum grows in quite damp soil,[12] but also on drier rough grassland, roadsides and disturbed ground. It is used as a food plant by the larvae of some lepidoptera, including silver-ground carpet moths and particularly the poison hemlock moth (Agonopterix alstroemeriana). The latter has been widely used as a biological control agent for the plant.[13] Poison hemlock grows in the spring, when much undergrowth is not in flower and may not be in leaf. All plant parts are poisonous.

Vernacular names in the English language are poison hemlock, poison parsley, spotted corobane (rarer forms), carrot fern (Australian Eng.), devil's bread or devil's porridge (Irish Eng.)[10]

Conium comes from the Ancient Greek κώνειον – kṓneion: "hemlock". This may be related to konas (meaning to whirl), in reference to vertigo, one of the symptoms of ingesting the plant.[14]

The plant should not be visually confused with the North American-native Tsuga, a coniferous tree sometimes called the hemlock, hemlock fir or hemlock spruce, from a slight similarity in the leaf smell. The ambiguous shorthand of 'hemlock' for this tree is more common in the US dialect than the plant it's actually named after.

Similarly, the plant should not be confused with Cicuta (commonly known as water hemlock).

Poison hemlock contains coniine and some similar poisonous alkaloids, and is poisonous to all mammals (and many other organisms) that eat it. Intoxication has been reported in cattle, pigs, sheep, goats, donkeys, rabbits, and horses. Ingesting less than a tenth of a gram of coniine, approximately equivalent to six to eight hemlock leaves, can be fatal for adult humans. The seeds and roots are also toxic, more so than the leaves.[15] While hemlock toxicity primarily results from consumption, poisoning can also result from inhalation, and from skin contact.[16] Farmers also need to be careful that the hay fed to animals does not contain hemlock. Poison hemlock is most poisonous in the spring when the concentration of γ-coniceine (the precursor to other toxins) is at its peak.[17][18]

Poison hemlock grows quite tall, reaching heights of up to twelve feet (3.6 meters).[19] The stalk of hemlock is green with purple spots and completely lacks hair. A biennial plant, hemlock produces leaves at its base the first year but no flowers. In its second year it produces white flowers in umbrella shaped clusters.[20] Hemlock can be confused with the wild carrot plant; however, this plant has a hairy stem without purple markings, grows less than three feet tall, and does not have clustered flowers.[16]

Alkaloids

Chemical structure of one of the two enantiomers, the (S)-(+) isomer, of coniine, where natural mixtures are considered likely racemates (equal mixtures) of this and the (R)-(–) isomer.[21]

C. maculatum is known for being extremely poisonous. Its tissues contain different alkaloids. In flower buds, the major alkaloid found is γ-coniceine. This molecule is transformed into coniine later during the fruit development.[22] The alkaloids are volatile; therefore, researchers assume that these alkaloids play an important role in attracting pollinators such as butterflies and bees.[23]

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.[8][24][25][26]

Coniine has a chemical structure and pharmacological properties similar to that of nicotine.[8][27] 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.[25] With its high potency, the ingestion of seemingly small doses can easily result in respiratory collapse and death.[28]

The alkaloid content found in C. maculatum also affects the thermoregulatory center by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves.[29] 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.[30]

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 kidney injury.[31] Coniine is toxic for the kidneys because it leads to the constriction of the urinary bladder sphincter and eventually the accumulation of urine.[32]

Conium maculatum is the plant that killed Theramenes, Socrates and Phocion.[35] 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 minds of the young men of Athens in 399 BC and his trial gave down his death sentence. He decided to take a potent infusion of hemlock. Plato described Socrates' death in the Phaedo:[36]

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.[37]

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 such poisoning.[38]

Perhaps he was murdered via an extract from an Aconitum species, such as Aconitum napellus, rather than via Conium maculatum as it too was commonly used by the Greeks as an arrow poison but can be used for other forms of poisoning; it has been hypothesized that Alexander the Great was murdered via aconite.[39] Some readers attributing a precise account to all of the somewhat sketchy and not always faithful accounts have suggested the drink was heavily dosed with opium, due to no involuntary spasms nor sign of pain he showed.[39]

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  Poison hemlock
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  Conium maculatum in Chino, California
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  Hemlock seed heads in late summer
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  The Death of Socrates, by Jacques-Louis David (1787)

• List of poisonous plants

Wikisource has the text of the 1905 New International Encyclopedia article "Hemlock".

• "Conium". Flora Europaea. Royal Botanic Garden Edinburgh.

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