Conium maculatum

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Conium maculatum
Conium.jpg
Conium maculatum in California
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Apiales
Family: Apiaceae
Genus: Conium
Species:
C. maculatum
Binomial name
Conium maculatum
L., 1753
Synonyms[1]
List
  • Cicuta major Lam.
  • Cicuta officinalis Crantz
  • Conium ceretanum Sennen
  • Conium cicuta (Crantz) Neck.
  • Conium croaticum Waldst. & Kit. ex Willd.
  • Conium divaricatum Boiss. & Orph.
  • Conium leiocarpum (Boiss.) Stapf
  • Conium maculosum Pall.
  • Conium nodosum Fisch. ex Steud.
  • Conium pyrenaicum Sennen & Elias
  • Conium sibiricum Steud.
  • Conium strictum Tratt.
  • Conium tenuifolium Mill.
  • Coriandrum cicuta Crantz
  • Coriandrum maculatum (L.) Roth
  • Selinum conium (Vest) E.L. Krause
  • Sium conium Vest
A 19th-century illustration of C. maculatum

Conium maculatum, the hemlock, poison hemlock or wild 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 Australia, West Asia, and North and South America, to which it has been introduced. It is capable of spreading and thereby becoming an invasive weed.

All parts of the plant are toxic, especially the seeds and roots, and especially when ingested. Under the right conditions the plant grows quite rapidly during the growing season and can reach heights of 8 feet (2.4 m), with a long penetrating root. The plant has a distinctive odor usually considered unpleasant that carries with the wind. The hollow stems are usually spotted with a dark maroon color before the plant dies and becomes dry and brown after completing its biennial lifecycle.

Taxonomy[edit]

The genus name "Conium" references the Greek koneios word for 'spin' or 'whirl', alluding to the dizzying effects of the plant's poison after ingestion. In the vernacular, "hemlock" most commonly refers to the species C. maculatum. 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.[2]

C. maculatum, also known as poison hemlock, was the first species within the genus to be described. It was identified by Carl Linnaeus in his 1753 publication, Species Plantarum. Maculatum means 'spotted', referencing the purple blotches characteristic of the stalks of this species.[3]

Names and similar plants[edit]

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.)[4]

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 is actually named after.[citation needed]

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

Wild poison hemlock also can be confused for Queen Anne's lace, which is wild or feral carrot plants and sometimes gathered and eaten as an edible wildflower. The authentic, edible plant lacks the purple mottling of hemlock on its stems, which in the case of Queen Anne's lace are also more hairy.[5]

Description[edit]

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.[6] Hemlock's flower is small and white; they are loosely clustered and each flower has five petals.[7] 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.[8] It can be confused with harmless cow parsley (Anthriscus sylvestris).[citation needed]

Distribution[edit]

The hemlock plant is native to Europe and the Mediterranean region.[9]

It exists in some woodland (and elsewhere) in most British Isles counties;[10] in Ulster these are particularly Down, Antrim and Londonderry.[11]

It has become naturalised in Asia, North America, Australia and New Zealand.[12][13][4] It is sometimes encountered around rivers in southeast Australia and Tasmania.[citation needed]

In the U.S., it is an introduced species found in nearly every state.[14]

Ecology[edit]

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[12] Conium maculatum grows in quite damp soil,[15] 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.[16] Poison hemlock grows in the spring, when much undergrowth is not in flower and may not be in leaf. All plant parts are poisonous.[citation needed]

Toxicity[edit]

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 more than 150–300 mg of coniine, approximately equivalent to six to eight hemlock leaves, can be fatal for adult humans.[17] The seeds and roots are also toxic, more so than the leaves.[18] While hemlock toxicity primarily results from consumption, poisoning can also result from inhalation, and from skin contact.[19][better source needed] 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.[20][21]

Poison hemlock grows quite tall, reaching heights of up to twelve feet (3.6 meters).[22] 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.[23] Hemlock can be confused with the wild carrot plant; however, the wild carrot plant has a hairy stem without purple markings, grows less than three feet tall, and does not have clustered flowers.[19]

Alkaloids[edit]

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.[24]

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.[25] The alkaloids are volatile; therefore, researchers assume that these alkaloids play an important role in attracting pollinators such as butterflies and bees.[26]

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.[12][27][28][29]

Coniine has a chemical structure and pharmacological properties similar to that of nicotine.[12][30] 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.[28] With its high potency, the ingestion of seemingly small doses can easily result in respiratory collapse and death.[31]

The alkaloid content found in C. maculatum also affects the thermoregulatory center by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves.[32] 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.[33]

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.[34] Coniine is toxic for the kidneys because it leads to the constriction of the urinary bladder sphincter and eventually the accumulation of urine.[35]

Toxicology[edit]

A short time after ingestion, the alkaloids produce potentially fatal neuromuscular dysfunction due to failure of the respiratory muscles. Acute toxicity, if not lethal, may resolve in spontaneous recovery, provided further exposure is avoided. Death can be prevented by artificial ventilation until the effects have worn off 48–72 hours later.[12] 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. Narcotic-like effects can be observed as soon as 30 minutes after ingestion of green leaf matter of the plant, with victims falling asleep and unconsciousness gradually deepening until death a few hours later.[36]

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.[37]

It has been observed that poisoned animals return to feed on the plant after initial poisoning. Chronic toxicity affects only pregnant animals when they are poisoned at low levels by C. maculatum during the fetus' organ-formation period, the offspring is born with malformations, mainly palatoschisis and multiple congenital contractures (arthrogryposis). The damage to the fetus due to 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.[citation needed]

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, and scientific studies have disproven these claims.[38]

Historical and cultural references[edit]

Conium maculatum is the plant that killed Theramenes, Socrates and Phocion.[39] 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:[40]

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.[41]

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.[42]

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.[43] 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.[43]

See also[edit]

References[edit]

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  15. ^ Online Atlas of the British and Irish Flora: Conium maculatum
  16. ^ Castells, Eva; Berenbaum, May R. (June 2006). "Laboratory Rearing of Agonopterix alstroemeriana, the Defoliating Poison Hemlock (Conium maculatum L.) Moth, and Effects of Piperidine Alkaloids on Preference and Performance". Environmental Entomology. 35 (3): 607–615. doi:10.1603/0046-225x-35.3.607. S2CID 45478867.
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  23. ^ "Poison Hemlock" (PDF). store.msuextension.org. Montana State University. Retrieved 3 May 2015.
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  37. ^ "Conium maculatum L." Inchem. IPCS (International Programme on Chemical Safety). Retrieved 2012-07-06.
  38. ^ Frank, A. A.; Reed, W.M. (April 1990). "Comparative Toxicity of Coniine, an Alkaloid of Conium maculatum (Poison Hemlock), in Chickens, Quails, and Turkeys". Avian Diseases. 34 (2): 433–437. doi:10.2307/1591432. JSTOR 1591432. PMID 2369382.
  39. ^ Blamey, M.; Fitter, R.; Fitter, A. (2003). Wild flowers of Britain and Ireland: The Complete Guide to the British and Irish Flora. London: A & C Black. ISBN 978-1408179505.
  40. ^ "Plato, Euthyphro, Apology, Crito, Phaedo". Archived from the original on 2012-07-20. Retrieved 2012-07-06.
  41. ^ Plato, Phaedo 117e–118a. Translated by Loeb Classical Library (1990 ed.). Cambridge, Massachusetts: Harvard University Press. pp. 401–3.
  42. ^ Bloch, E. (March 2001). "Hemlock Poisoning and the Death of Socrates: Did Plato Tell the Truth?". Journal of the International Plato Society. Archived from the original on 2017-04-07.
    – An expanded version of this article was also printed in Bloch, E. (2002). Brickhouse, Thomas C.; Smith, Nicholas D. (eds.). The Trial and Execution of Socrates: Sources and Controversies. New York: Oxford University Press. ISBN 978-0-19-511980-0.
  43. ^ a b Hayes, Antoinette; Gilbert, Stephen (2009). "Historical milestones and discoveries that shaped the toxicology sciences". In Luch, A. (ed.). Molecular, Clinical and Environmental Toxicology. Volume 1: Molecular Toxicology. Experientia Supplementum. 99. Switzerland: Birkhäuser Verlag. pp. 6–7. doi:10.1007/978-3-7643-8336-7_1. ISBN 978-3-7643-8335-0. PMID 19157056. Retrieved 11 February 2020.

External links[edit]

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