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Conium maculatum, commonly known as hemlock (British English) or poison hemlock (in North America), is a highly poisonous flowering plant in the carrot family Apiaceae.
The plant is herbaceous, with no woody parts, and has a Biennial plant lifecycle. Under the right conditions, the plant grows quite rapidly during the growing season and can reach heights of with a long Taproot. 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 and North 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 an Invasive plant weed.
All parts of the plant are Toxic plant, particularly the seeds and roots, and especially when ingested. Hemlock is well-known as the poison that killed the philosopher Socrates after his trial in Ancient Greece.
The leaves 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. They are broad with an overall triangular shape, some in length. The leaflets are attached in pairs on opposite sides of the central veins.
The poison hemlock's flowers are small and white; each flower has five petals and lacks . (1997). 9780471047018, Wiley. ISBN 9780471047018 The flowers have white and a style that measures about 0.5 mm. The flowers are in umbrella shaped clusters called . They measure in diameter and are found both at the end of stem branches and growing from the , the angle created where the leaf stem joins the main stems of the plant. Each umbel is a circular cluster of ten to twenty rays, the short stems 1 to 3.5 cm long, radiating out from its center.
The fruit is a schizocarp, it can easily be separated into two parts. The fruits measure 2.5 to 3.5 mm long and are gray-brown with ridges and have an egg shaped outline.
Wild carrot has a hairy stem without purple markings, and grows less than tall. 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 —twice the maximum for wild carrot.
Hemlock can be confused with harmless cow parsley ( Anthriscus sylvestris), the wild herb Chaerophyllum macropodum used in Turkish cheesemaking, and deadly water hemlock ( Cicuta). Water hemlock lacks the purple spots and the disagreeable mouse like smell of hemlock and has a branching tuber that grows sideways in the soil instead of a vertical taproot. (2025). 9780471727613, John Wiley & Sons. ISBN 9780471727613
C. maculatum was the first species within the genus Conium to be described. It was identified by Carl Linnaeus in his 1753 publication, Species Plantarum. Maculatum means 'spotted', in reference to the purple blotches on the plant's stalks and is derived from the Latin macula.
Conium maculatum has synonyms, 16 of them species, according to Plants of the World Online.
In American English and Canadian English, it is typically called poison hemlock, though this name is also used elsewhere. This usage dates to 1757. Less frequent names used in both America and Australia include spotted hemlock and poison parsley. 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. In Australia, it is occasionally called wild carrot or wild parsnip. In Canada, is it is also known as common poison-hemlock, deadly hemlock, fool's-parsley, spotted parsley, and spotted-hemlock.
It is also utilized as a food source by caterpillars of the North American black swallowtail butterfly, though they have greater success on two other introduced plants, wild carrots and parsnips. Similarly, the anise swallowtail ( Papilio zelicaon) in western North America depends largely on non-native plants like hemlock and fennel in urban and suburban areas of California.
The main toxic alkaloids are coniine and γ-coniceine, also called gamma-coniceine. Intoxication is reported in pigs, cattle, elk, turkeys, sheep, rabbits, sheep, goats, donkeys, and horses. However, are less sensitive and have reportedly become toxic from absorbing the coniine from hemlock. Ingesting more than 150–300 milligrams of coniine, approximately equivalent to six to eight hemlock leaves, can be fatal for adult humans.
Grazing animals are most likely to be poisoned in the spring when other forage is unavailable. However, they may also be poisoned when hemlock has become mixed into grain, hay, or silage.
Hemlock was one of many plants suggested by medieval writers as a possible cause of coturnism, a disease caused by eating common quail in certain seasons. Modern research focuses on annual woundwort ( Stachys annua) as the most likely source of the toxin, though the cause is still unknown.
The major alkaloid found in flower buds is γ-coniceine. This molecule is transformed into coniine during the later stages of fruit development. The alkaloids are volatile; as such, researchers assume that these alkaloids play an important role in attracting , such as butterflies and bees.
In labrotory experiments on mice, γ-coniceine was lethal at just 0.14 the equivelent dose of coninne while N-methylconiine took 1.5 times the equivelent 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.
The alkaloid content in C. maculatum affects the thermoregulatory centre by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves. In addition, the alkaloid content stimulates the sympathetic ganglia and reduces the influence of the parasympathetic ganglia in rats and rabbits, causing an increased heart rate.
Coniine has significant toxic effects on the kidneys. The presence of rhabdomyolysis and acute tubular necrosis has been demonstrated in patients who died from hemlock poisoning. Some of these patients had acute kidney injury. Contact of the leaves with bare skin can result in rash and persistent blisters through phototoxicity, the sensitisation of the skin to sunlight.
Shortly after ingestion, the alkaloids induce neuromuscular dysfunction that is potentially fatal due to failure of the respiratory muscles. Acute toxicity, if not lethal, may be followed by spontaneous recovery, provided further exposure is avoided. Death can be prevented by artificial ventilation until the effects wear off after 48–72 hours. 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. Unconsciousness-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. The onset of symptoms is similar to that caused by curare, with an ascending muscular paralysis leading to paralysis of the respiratory muscles and ultimately death by oxygen deprivation.
As there is no specific antidote, prevention is the only way to deal with agricultural production losses caused by the plant. The use of 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 via milk and fowl.
by Jacques-Louis David, 1787
Hemlock was used as a medicine in ancient times, though great care was required due to its toxic properties. In Medieval Europe, it was only administered as a remedy for "the bite of mad dogge" in wine together with Stachys and fennel 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 from gout. The popular herbalist Nicholas Culpeper wrote that it was under the control of Saturn 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.
In the Victorian language of flowers, hemlock flowers were used as a symbol meaning, "You will be the death of me". From 1864 to 1898 hemlock was officially listed as a medicine in the London and Edinburgh pharmacopoeias. The last listing of it was in the British Pharmaceutical Codex in 1934.
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