Conium maculatum

''Conium maculatum'', commonly known as hemlock (British English) or poison hemlock (American English), is a highly poisonous flowering plant in the carrot family Apiaceae, native to Europe and North Africa. It is herbaceous, with no woody parts, and has a biennial lifecycle. Hemlock is a hardy plant capable of living in a variety of environments and is now widely naturalised in locations outside its native range, including 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 hemlock plant are toxic, particularly 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 , with a long penetrating 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. The hollow stems of the plant remain deadly for up to three years after the plant has died.

Description

''Conium maculatum'' is a herbaceous flowering plant that grows to tall, exceptionally . All parts of the plant are hairless (glabrous). Hemlock has a stem that is smooth, green, and hollow, usually spotted or streaked with red or purple. The leaves are two- to four-pinnate, finely divided and lacy, overall triangular in shape, up to long and broad. Hemlock's flower is small and white; they are loosely clustered and each flower has five petals.

A biennial plant, hemlock produces leaves at its base in its first year but no flowers. In its second year, it produces white flowers in umbrella-shaped clusters.

Similar species

Hemlock can be confused with the wild carrot plant (''Daucus carota'', sometimes called Queen Anne's lace). 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 being at least —twice the maximum for wild carrot. Wild carrots have hairy stems that lack the purple blotches.
The species can also be confused with harmless cow parsley ('' Anthriscus sylvestris,'' also sometimes called Queen Anne's lace).

The plant should not be visually confused with the North American coniferous tree ''Tsuga'', which is sometimes called hemlock, hemlock fir, or hemlock spruce due to a slight similarity in the leaf smell. The ambiguous shorthand term 'hemlock' for this tree is more common in US dialects than the plant it is actually named after. Similarly, the plant should not be confused with '' Cicuta'' (commonly known as water hemlock).

Taxonomy

The genus name "Conium" refers to ''koneios'', the Greek 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.

''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', in reference to the purple blotches characteristic of the stalks of the species.

Names

In British and Australian English, the most prominent vernacular name is hemlock. In American English, it is typically called poison hemlock, though this name is also used elsewhere. Less frequent names used in both America and Australia include spotted hemlock and poison parsley. Other local or infrequent names in the US include: bunk, California-ferm, cashes, herb-bonnet, kill-cow, Nebraska-fern, poisonroot, poison-snakeweed, St. Bennet's-herb, snakeweed, stinkweed, and wode-whistle. In Australia, it is occasionally called wild carrot or wild parsnip. In Hiberno-English, it may be called devil's bread or devil's porridge.

Distribution and habitat

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

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

It has become naturalised in Asia, North America, Australia, and New Zealand. See also the substituent page: It is sometimes encountered around rivers in southeast Australia and Tasmania. Infestations and human contact with the plant are sometimes newsworthy events in the U.S. due to its extreme toxicity.

Ecology

The plant is often found in poorly drained soil, particularly near streams, ditches, and other watery surfaces. It also grows on roadsides, at the edges of cultivated fields and in waste areas. ''Conium maculatum'' grows in quite damp soil, 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. Hemlock grows in the spring, when much undergrowth is not in flower and may not be in leaf. All parts of the plant are poisonous.

Toxicity

Hemlock contains coniine and some similar poisonous alkaloids, and is poisonous to all mammals (and many other organisms) that ingest it. Intoxication has been reported in cattle, pigs, sheep, goats, donkeys, rabbits, and horses. Ingesting more than 150–300 milligrams of coniine, approximately equivalent to six to eight hemlock leaves, can be fatal for adult humans. The seeds and roots are more toxic than the leaves. Farmers also need to ensure that the hay fed to their animals does not contain hemlock. Hemlock is at its most poisonous in the spring when the concentration of γ-coniceine (the precursor to other toxins) is at its peak.

Alkaloids

''C. maculatum'' is known for being extremely poisonous. Its tissues contain a variety of different alkaloids. 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 pollinators, such as butterflies and bees.

''Conium'' contains the piperidine alkaloids coniine, N-methylconiine, conhydrine, , and gamma-coniceine (or g-coniceïne), which is the precursor of the other hemlock alkaloids.

Coniine has pharmacological properties and a chemical structure similar to nicotine. Coniine acts directly on the central nervous system through inhibitory action on nicotinic acetylcholine receptors. Coniine can be dangerous to humans and livestock, and with its high potency, the ingestion of seemingly small doses can easily result in respiratory collapse and death.

The alkaloid content in ''C. maculatum'' also affects the thermoregulatory centre by a phenomenon called peripheral vasoconstriction, resulting in hypothermia in calves. In addition, the alkaloid content 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.

Coniine also 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 were also found to have acute kidney injury. Coniine is toxic for the kidneys because it leads to the constriction of the urinary bladder sphincter, eventually resulting in the accumulation of urine.

Toxicology

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 result in 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. Narcotic-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.

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 formation of the fetus's organs. In such cases, the offspring is born with malformations, mainly palatoschisis and multiple congenital contractures (arthrogryposis). The damage caused to the fetus due to chronic toxicity is irreversible. Although arthrogryposis can sometimes be surgically corrected, most malformed animals die. Such losses may be underestimated, at least in some regions, due to the difficulty of associating malformations with maternal poisoning at a much earlier stage.

As there is no specific antidote available, prevention is the only way to deal with the production losses caused by the plant. The use of herbicides 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 ''C. maculatum'' alkaloids can enter the human food chain via milk and fowl.

Culture

In ancient Greece, hemlock was used to poison condemned prisoners. ''Conium maculatum'' is the plant that killed Theramenes, Socrates, Polemarchus, and Phocion. 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 was sentenced to death at his trial. He decided to take a potent infusion of hemlock.

See also

* List of poisonous plants

References

External links

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Apioideae
Flora of Europe
Plants described in 1753
Taxa named by Carl Linnaeus