Conium maculatum

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
Conium maculatum in California
Scientific classification
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]
A 19th-century illustration of C. maculatum

Name

Conium maculatum is known by several common names. In addition to the British hemlock, the Australian carrot fern[2] 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.[3]

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 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.[4]

Description

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.[5] 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.[6]

It has been introduced and naturalised in many other areas, including Asia, North America, Australia and New Zealand.[7][8][2] 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[7] and is considered an invasive species in 12 U.S. states.[9]

Conium maculatum grows in damp areas,[10] 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.[11] 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.

Distribution

Recorded from the British Isles.[12] In Ireland this species has been recorded from Counties Down, Antrim and Londonderry.[13]

Toxicity

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
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.[14]

C. maculatum is known for its poisonous characteristic. Its 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.[15] The alkaloids are volatile; therefore, researchers assume that these alkaloids play an important role in attracting pollinators such as butterflies and bees.[16]

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.[7][17][18][19]

Coniine has a chemical structure and pharmacological properties similar to that of nicotine.[7][20] 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.[18] With its high potency, the ingestion of seemingly small doses can easily result in respiratory collapse and death.[21]

The alkaloid content found in C. maculatum also affects the thermoregulatory center by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves.[22] 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.[23]

One of the reasons poison hemlock is appealing to herbivores and other animals is its appearance. Poison hemlock leaves look similar to those of carrots or parsley; therefore, animals often mistake hemlock for common edible plants. Also, due to its abundance in early spring, at certain points of the year, poison hemlock is more accessible to animals than edible forage.

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.[24] Coniine is toxic for the kidneys because it leads to the constriction of the urinary bladder sphincter and eventually the accumulation of urine.[25]

Toxicology

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.

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.[7] 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.[26]

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.

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.[27]

Historical and cultural references
Main article: Socrates § Death

Conium maculatum is the plant that killed Theramenes, Socrates and Phocion.[28] 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:[29]

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.[30]

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, 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.[31]

It has also been hypothesized that he was murdered via an extract from an Aconitum species, such as Aconitum napellus, rather than via Conium maculatum. Aconitum was commonly used by the Greeks as an arrow poison but can be used for other forms of poisoning. For instance, it has been hypothesized that Alexander the Great was murdered via aconite.[32] It has also been suggested that his drink was heavily dosed with opium, due to the relative placidity of his expiration.[32]

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

See also
  • List of poisonous plants

References
  1. Allkin, R.; Magill, R.; et al., eds. (2013). "Conium maculatum L." The Plant List (online database). 1.1. Retrieved January 23, 2017.
  2. Atlas of Living Australia, Conium maculatum L., Carrot Fern
  3. "Kex". EtymOnline.
  4. "Conium maculatum". Northwestern Arizona University. Retrieved 2012-07-06.
  5. Altervista Flora Italiana, Cicuta maggiore, Conium maculatum L. includes photos and European distribution map
  6. Holm, LeRoy G. (1997). World weeds: natural histories and distribution. New York: Wiley. ISBN 0471047015.
  7. Schep, L. J.; Slaughter, R. J.; Beasley, D. M. (2009). "Nicotinic Plant Poisoning". Clinical Toxicology. 47 (8): 771–781. doi:10.1080/15563650903252186. PMID 19778187.
  8. Zehui, Pan & Watson, Mark F. "31. Conium Linnaeus, Sp. Pl. 1: 243. 1753". Flora of China. Retrieved January 23, 2017. See also the substituent page: "1. Conium maculatum Linnaeus, Sp. Pl. 1: 243. 1753". Flora of China. Retrieved January 23, 2017.
  9. "Poison hemlock, spotted hemlock – Conium maculatum". Map, where regarded invasive. National Park Service. Retrieved 2009-01-14.
  10. Online Atlast of the British and Irish Flora: Conium maculatum
  11. 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.
  12. Clapham, A.R.; Tutin, T.G.; Warburg, E.F. (1968). Excursion Flora of the British Isles (2nd ed.). ISBN 0521-04656-4.
  13. Hackney, P., ed. (1992). Stewart & Corry's Flora of the North-east of Ireland. Institute of Irish Studies and The Queen's University of Belfast. ISBN 0-85389-446-9.
  14. Stephen T. Lee; Benedict T. Green; Kevin D. Welch; James A. Pfister; Kip E. Panter (2008). "Stereoselective potencies and relative toxicities of coniine enantiomers". Chemical Research in Toxicology. 21 (10): 2061–2064. doi:10.1021/tx800229w. PMID 18763813.
  15. Cromwell, B. T. (October 1956). "The separation, micro-estimation and distribution of the alkaloids of hemlock (Conium maculatum L.)". Biochemical Journal. 64 (2): 259–266. doi:10.1042/bj0640259. ISSN 0264-6021. PMC 1199726. PMID 13363836.
  16. Roberts, Margaret F. (1998), "Enzymology of Alkaloid Biosynthesis", Alkaloids, Springer US, pp. 109–146, doi:10.1007/978-1-4757-2905-4_5, ISBN 9781441932631
  17. Reynolds, T. (June 2005). "Hemlock Alkaloids from Socrates to Poison Aloes". Phytochemistry. 66 (12): 1399–1406. doi:10.1016/j.phytochem.2005.04.039. PMID 15955542.
  18. Vetter, J. (September 2004). "Poison Hemlock (Conium maculatum L.)". Food and Chemical Toxicology. 42 (9): 1373–1382. doi:10.1016/j.fct.2004.04.009. PMID 15234067.
  19. "Conium maculatum TOXINZ - Poisons Information". www.toxinz.com. Retrieved 2017-05-29.
  20. Brooks, D. E. (2010-06-28). "Plant Poisoning, Hemlock". MedScape. eMedicine. Retrieved 2012-03-02.
  21. Tilford, Gregory L. (1997). Edible and Medicinal Plants of the West. ISBN 978-0-87842-359-0.
  22. López, T.A.; Cid, M.S.; Bianchini, M.L. (June 1999). "Biochemistry of hemlock (Conium maculatum L.) alkaloids and their acute and chronic toxicity in livestock. A review". Toxicon. 37 (6): 841–865. doi:10.1016/s0041-0101(98)00204-9. ISSN 0041-0101. PMID 10340826.
  23. Forsyth, Carol S.; Frank, Anthony A. (July 1993). "Evaluation of developmental toxicity of coniine to rats and rabbits". Teratology. 48 (1): 59–64. doi:10.1002/tera.1420480110. ISSN 0040-3709. PMID 8351649.
  24. Note:acute tubular necrosis causes acute kidney injury. Rizzi, D; Basile, C; Di Maggio, A; et al. (1991). "Clinical spectrum of accidental hemlock poisoning: neurotoxic manifestations, rhabdomyolysis and acute tubular necrosis". Nephrol. Dial. Transplant. 6 (12): 939–43. doi:10.1093/ndt/6.12.939. PMID 1798593.
  25. Barceloux, Donald G. (2008), "Poison Hemlock (Conium maculatum L.)", Medical Toxicology of Natural Substances: Foods, Fungi, Medicinal Herbs, Plants, and Venomous Animals, John Wiley & Sons, Inc., pp. 796–799, doi:10.1002/9780470330319.ch131, ISBN 9780470330319
  26. "Conium maculatum L." Inchem. IPCS (International Programme on Chemical Safety). Retrieved 2012-07-06.
  27. 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.
  28. 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.
  29. "Plato, Euthyphro, Apology, Crito, Phaedo". Archived from the original on 2012-07-20. Retrieved 2012-07-06.
  30. Plato, Phaedo 117e–118a. Translated by Loeb Classical Library (1990 ed.). Cambridge, Massachusetts: Harvard University Press. pp. 401–3.
  31. 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.
  32. 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. Retrieved 11 February 2020.
  • "Conium". Flora Europaea. Royal Botanic Garden Edinburgh.
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