Conium maculatum, commonly known ashemlock (British English) orpoison hemlock (in North America), is a highly poisonousflowering plant in the carrot familyApiaceae.
The plant isherbaceous, with no woody parts, and has abiennial lifecycle. Under the right conditions, the plant grows quite rapidly during the growing season and can reach heights of 2.4 metres (8 feet) with a longpenetrating root. The plant has a distinctive odour that is usually considered unpleasant and carries with the wind. The hollow stems are usually spotted dark maroon and turn dry and brown after the plant completes its biennial lifecycle.
Native to Europe andNorth Africa, hemlock is a hardy plant that can live in a variety of environments. It is widely naturalised outside its native range, including in Australia, West Asia, and North and South America, where it can become aninvasiveweed.
All parts of the plant aretoxic, particularly the seeds and roots, and especially when ingested. Hemlock is well-known as the poison that killed the philosopherSocrates afterhis trial inAncient Greece.
Conium maculatum is a herbaceousflowering plant that typically grows as abiennial, but can grow as aperennial on occasion.[2] The second year stems topped with flowers grow to between 0.5 and 3 m (1.6 and 9.8 ft) in height;[3] they are coarse and branch frequently.[4] Stems are hollow except at the joints where the leaves are attached and are generally spotted or streaked with purple.[2][5] In the first year of growth, the plant has no stems and produces a largerosette of leaves.[2] All parts of the plant areglabrous, lacking hairs, but sometimes they will have a small amount of blue-grey natural waxes on lower parts of the plant.[6] Thetaproot is long, white, has a fleshy texture, and is usually unbranched.[7]
Theleaves are one- to three-pinnate, finely divided and lacy. The leaves lower down on the plant are two-pinnate or more, while the upper leaves are one-pinnate and often only partly divided. The lower leaves are larger than those higher up.[3] They are broad with an overall triangular shape, some 30 to 60 cm (12 to 24 in) in length.[6] The leaflets are attached in pairs on opposite sides of the central veins.[4]
The poison hemlock's flowers are small and white; each flower has five petals and lackssepals.[8] The flowers have whitestamens and astyle that measures about 0.5 mm. The flowers are in umbrella shaped clusters calledumbels.[3] They measure 2 to 5 cm (0.8 to 2.0 in) in diameter and are found both at the end of stem branches and growing from theaxils, the angle created where the leaf stem joins the main stems of the plant. Eachumbel is a circular cluster of ten to twenty rays, the short stems 1 to 3.5 cm long, radiating out from its center.[9]
The fruit is aschizocarp,[8] it can easily be separated into two parts.[10] The fruits measure 2.5 to 3.5 mm long and are gray-brown with ridges and have an egg shaped outline.[9][10]
The wild carrot,Daucus carota, is often confused with poison hemlock.
Hemlock can be confused with several other species in the parsley family with potentially fatal results. Edible plants that can be confused with hemlock include cultivatedcarrots and thewild carrot (Daucus carota),parsnip (Pastinaca sativa),fennel (Foeniculum vulgare), andparsley (Petroselinum crispum).[11]
Wild carrot has a hairy stem without purple markings, and grows less than 1 m (3+1⁄2 ft) tall.[12] One can distinguish the two from each other by hemlock's smooth texture, vivid mid-green colour, purple spotting of stems and petioles, and flowering stems reaching a typical height of at least 1.5 m (5 ft)—twice the maximum for wild carrot.[13][14]
Hemlock can be confused with harmless cow parsley (Anthriscus sylvestris),[2][15] the wild herbChaerophyllum macropodum used in Turkish cheesemaking,[16] and deadly water hemlock (Cicuta).[15] Water hemlock lacks the purple spots and the disagreeable mouse like smell of hemlock and has a branchingtuber that grows sideways in the soil instead of a verticaltaproot.[17]
The generic nameConium comes from theAncient Greek κώνειονkṓneion: "hemlock". This may be related tokonas (meaning to whirl), in reference tovertigo, one of the symptoms of ingesting the plant.[18]
C. maculatum was the first species within the genusConium to be described. It was identified byCarl Linnaeus in his 1753 publication,Species Plantarum.[19]Maculatum means 'spotted', in reference to the purple blotches on the plant's stalks and is derived from the Latinmacula.[20]
InBritish,Australian, andNew Zealand English, the most prominentvernacular name is hemlock.[21][22][8] This name is derived from theOld English wordshymlice,hymlic, orhemlic, likely referring toConium. More certainly in the 1500s, it referred toConium maculatum and was used in herbalist texts. It enteredMiddle English ashemeluc,hemlok,hemlake,hemlocke,hemloc, orhemblock. In this period, it was first spelled ashemlock by William Shakespeare in his playHenry V in 1623.[23] The herbaceous plant is unrelated toconiferous trees in the genusTsuga, which are also called hemlocks and were thought to have a similar smell.[24]
InAmerican andCanadian English,[25][26] it is typically called poison hemlock, though this name is also used elsewhere.[22] This usage dates to 1757.[27] Less frequent names used in both America and Australia include spotted hemlock and poison parsley.[28][22] Other local or infrequent names in the United States include bunk, California-fern, cashes, herb-bonnet, kill-cow, Nebraska-fern, poisonroot, poison-snakeweed, poison stinkweed, St. Bennet's-herb, snakeweed, stinkweed, winter fern, and wode-whistle.[28][29] In Australia, it is occasionally called wild carrot, wild parsnip,[22] or snakeweed.[30] In Canada, is it is also known as common poison-hemlock, deadly hemlock, fool's-parsley, spotted parsley, and spotted-hemlock.[26]
The hemlock plant is native to Europe,Central Asia, and theMediterranean region.[31] It occurs in manyBritish Isles counties,[32] including in Northern Ireland.[33] It has become naturalised in Asia, North America, Australia, and New Zealand.[34][35][22] It is sometimes encountered around rivers insoutheast Australia andTasmania, where it has been considered aninvasive species.[36] Infestations and human contact with the plant are sometimes newsworthy events in the U.S. due to its toxicity.[37][38] It spreads rapidly by seed, and is hard to eradicate as the seeds can lie dormant for up to 6 years.[39]
The plant is often found in poorly drained soil, particularly near streams, ditches, and other watery surfaces. It grows on roadsides, at the edges of cultivated fields and in waste areas.[34] It grows in quite damp soil,[21] but also on drier rough grassland, roadsides, anddisturbed ground. It is used as a food plant by thelarvae of someLepidoptera, includingsilver-ground carpet moths and the poison hemlock moth (Agonopterix alstroemeriana). The latter has been widely used as a biological control agent for the plant.[40]
It is a food source for caterpillars of the North Americanblack swallowtail butterfly, though they have greater success on two other introduced plants, wild carrots and parsnips.[41] Similarly, theanise swallowtail (Papilio zelicaon) in western North America depends largely on non-native plants like hemlock and fennel in urban and suburban areas of California.[42]
Poison hemlock was introduced to the US from Europe in the 1800s as an ornamental garden plant called "winter fern".[43] With it came the poison hemlock moth, which has spread across most of the US, but its efficacy at destroying the plant has been limited. The plant may be adapting to its predators by becoming more toxic.[44]
All parts of the plant can be poisonous, but the total amount of poisonousalkaloids varies significantly with the age of the plant and between parts.[45] The roots of young, first year plants contain only traces of poison or none at all.[46][47] The leaves ofseedlings have lower levels of poison than slightly older plants. In the spring of the second year the leaves are highly toxic, though not as poisonous as the flowers or seeds later in the season.[46] The hollow stems remain deadly for up to three years after the plant has died.[48] However, drying causes the plant to lose a large part of its toxic compounds.[7] Plants which have grown in sunny conditions can be twice as poisonous as plants that grew in wet and cloudy conditions.[7]
The main toxic alkaloids areconiine and γ-coniceine,[16] also called gamma-coniceine.[49] Intoxication is reported in diverse groups of animals including pigs, bovids, turkeys, equines, rabbits,[16][50] cats, and dogs.[51] However,songbirds are less sensitive and have reportedly become toxic from absorbing the coniine from hemlock.[16] Ingesting more than 150–300 milligrams of coniine, approximately equivalent to six to eight hemlock leaves, can be fatal for adult humans.[50]
Grazing animals are most likely to be poisoned in the spring when otherforage is unavailable.[16] However, they may also be poisoned when hemlock has become mixed into grain,hay, orsilage.[49] Poison hemlock ingestion typically induces intense and fatal seizures in cattle. Even very small quantities have been shown to cause birth defects when ingested within 40-100 days of gestation.[52]
Hemlock was one of many plants suggested by medieval writers as a possible cause ofcoturnism, a disease caused by eatingcommon quail in certain seasons. Modern research focuses onannual woundwort (Stachys annua) as the most likely source of the toxin, though the cause is still unknown.[53]
The major alkaloid found in flower buds is γ-coniceine. This molecule is transformed into coniine during the later stages of fruit development.[58] The alkaloids are volatile; as such, researchers assume that these alkaloids play an important role in attractingpollinators, such as butterflies and bees.[59]
In laboratory experiments on mice, γ-coniceine was lethal at just 0.14 the equivalent dose of coninne while N-methylconiine took 1.5 times the equivalent dose of coniine when injected. Oral administration of coniine required about five times as much for a lethal dose. Comparied to coniine by oral administration γ-coniceine required 0.12 times as much and N-methylconiine required 2.0 times as much.[62]
Coniine has significant toxic effects on the kidneys. The presence ofrhabdomyolysis andacute tubular necrosis has been demonstrated in patients who died from hemlock poisoning. Some of these patients hadacute kidney injury.[65] Contact of the leaves with bare skin can result in rash and persistent blisters throughphototoxicity, the sensitisation of the skin to sunlight.[66]
Shortly after ingestion, the alkaloids induce neuromuscular dysfunction that is potentially fatal due to failure of therespiratory muscles.Acute toxicity, if not lethal, may be followed by spontaneous recovery, provided further exposure is avoided. Death can be prevented byartificial ventilation until the effects wear off after 48–72 hours.[34] 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.Narcosis-like effects can be observed as soon as 30 minutes after ingestion of green leaves of the plant, with victims falling asleep and gradually becoming unconscious until death occurs a few hours later.[67] The onset of symptoms is similar to that caused bycurare, with an ascending muscular paralysis leading to paralysis of the respiratory muscles and ultimately death by oxygen deprivation.[68]
The English physician and botanistJohn Harley worked with a preparation of hemlock calledsuccus conii, testing it on himself and recording the effects in his bookThe Old Vegetable Neurotics published in 1869.[69]
An hour and a quarter after taking the dose, I first felt decided weakness in my legs. The giddiness and diminution of motor power continued to increase for the next fifteen minutes. An hour and a half after taking the dose, these effects attained their maximum ; and at this time I was cold, pale, and tottering. ... The mind remained perfectly clear and calm, and the brain active throughout; but the body seemed heavy, and well-nigh asleep.[70]
As there is no specific antidote, prevention is the only way to deal with agricultural production losses caused by the plant. The use ofherbicides and grazing with less-susceptible animals (such as sheep) have been suggested as control methods. Contrary to popular belief, scientific studies have disproven the claim that the plant's alkaloids can enter the human food chain viamilk andfowl.[71]
In ancient Greece, hemlock was used to poison condemned prisoners.Conium maculatum is the plant that killedTheramenes,Socrates,Polemarchus, andPhocion.[72] Socrates, the most famous victim of hemlock poisoning, was sentenced to death athis trial; he took aninfusion of hemlock.[73] InGreek mythology, poisonous plants like hemlock were sacred to the goddessHecate and her daughtersCirce andMedea.[74]
Cups of the type used to administer hemlock poison in ancient Greece, 5th century BC
In high mountain areas ofGeorgia, hemlock leaves were used as a spring food after long winters. It required careful cooking, often in several changes of water. Other poisonous leaves used in this fashion includedcow parsnips (Heracleum species),potatoes, andlilies. Locals speaking toethnobotanical researchers knew the poisonous nature of the plants and reported the practice to have largely died out with better roads and greater availability of cultivated foods in markets.[75]
Hemlock was used as a medicine in ancient times, though great care was required due to its toxic properties. InMedieval Europe, it was only administered as a remedy for"the bite of mad dogge" (rabies) in wine together withbetony andfennel seed. Later uses included a final, desperate attempt to cure virulent poisons such as strychnine. In the 1400s and 1500s European monks roasted the root and applied it externally to the feet, hands, and wrists for pain fromgout.[76] The popular herbalistNicholas Culpeper wrote that it was under the control ofSaturn giving it a cold and dangerous character. He recommended it for external use for inflammation and swelling and the roasted root on the hands for gout.[74]
In the Victorianlanguage of flowers, hemlock flowers were used as a symbol meaning, "You will be the death of me".[29] From 1864 to 1898 hemlock was officially listed as a medicine in theLondon andEdinburgh pharmacopoeias. The last listing of it was in the British Pharmaceutical Codex in 1934.[62]
If the infestation is relatively small, it is recommended to dig out the entire plant including the roots with proper protective equipment. One should wear clothing that covers exposed skin, eye protection, and gloves. Many herbicides will also work for killing a spread of hemlock.[77]
^abcdPokorny, Monica; Davis, Stacy; Mangold, Jane (January 2018)."Poison HemlockConium maculatum"(PDF).Montana State University Extension.Archived(PDF) from the original on 30 July 2024. Retrieved22 August 2025.
^abcHolm, LeRoy G.; Doll, Jerry; Holm, Eric; Herberger, James (1997).World Weeds: Natural Histories and Distribution. New York:Wiley. pp. 223, 225.ISBN978-0-471-04701-8.OCLC34114783.
^Dauncey, Elizabeth A.; Larsson, Sonny (2018).Plants That Kill: A Natural History of the World's Most Poisonous Plants. Princeton, New Jersey: Princeton University Press. pp. 100−101.ISBN978-0-691-17876-9.OCLC1027707097.
^"Poison-hemlock".Noxious Weeds in King County, Weed Identification Photos. Seattle, Washington: Department of Natural Resources and Parks, Water and Land Resources Division, Rural and Regional Services section. November 28, 2016. RetrievedJanuary 23, 2017.
^abcdeFrohne, Dietrich; Pfänder, Hans Jürgen (2005) [Translated from German Fifth Edition 2004]. McKinney, Patrick; Cumpston, Kirk (eds.).Poisonous Plants: A Handbook for Doctors, Pharmacists, Toxicologists, Biologists and Veterinarians. Translated by Alford, Inge (Second ed.). Portland, Oregon:Timber Press. pp. 47–49.ISBN978-0-88192-750-4.OCLC59360317.
^Lee, Stephen T.; Green, Benedict T.; Welch, Kevin D.; Pfister, James A.; Panter, Kip E. (2008). "Stereoselective potencies and relative toxicities of coniine enantiomers".Chemical Research in Toxicology.21 (10):2061–2064.doi:10.1021/tx800229w.PMID18763813.
^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.PMID8351649.
^Rizzi, D.; Basile, C; Di Maggio, A.; et al. (1991). "Clinical spectrum of accidental hemlock poisoning: neurotoxic manifestations, rhabdomyolysis and acute tubular necrosis".Nephrology Dialysis Transplantation.6 (12):939–943.doi:10.1093/ndt/6.12.939.PMID1798593.
^Bloch, Enid (2002). "Hemlock Poisoning and the Death of Socrates: Did Plato Tell the Truth?". In Brickhouse, Thomas C.; Smith, Nicholas D. (eds.).The Trial and Execution of Socrates: Sources and Controversies. New York: Oxford University Press. pp. 256–259,261–264, 272.ISBN978-0-19-511980-0.OCLC47677838.
^Frank, A. A.; Reed, W. M. (April 1990). "Comparative Toxicity of Coniine, an Alkaloid ofConium maculatum (Poison Hemlock), in Chickens, Quails, and Turkeys".Avian Diseases.34 (2):433–437.doi:10.2307/1591432.JSTOR1591432.PMID2369382.
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