Conium maculatum
(poison hemlock)

Preferred Common Name

• poison hemlock

Other Scientific Names

• 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

International Common Names

• English: beaver poison; carrot-fern; fool's-parsley; hemlock; herb bennet; kecksies; kex; musquash root; poison parsley; spotted corobane; spotted-hemlock; spotted-parsley
• Spanish: encaje cimarrón; panalillo; perejil de chucho; perejil de monte; zanahoria silvestre
• French: cigue maculee; cigue tache; cigue tachetee; grande ciguë
• Chinese: du shen

Local Common Names

• Brazil: cicuta; funcho-selvagem
• Germany: Gefleckter Schierling
• Guatemala: perejil de chucho; perejil de monte
• Italy: cicuta maggiore
• Netherlands: gevlekte scheerling
• Sweden: odört

EPPO code

• COIMA (Conium maculatum)

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Apiales
•                         Family: Apiaceae
•                             Genus: Conium
•                                 Species: Conium maculatum

The derivation of the genus name Conium is uncertain, but may be from the Greek koneion meaning to whirl or spin, describing the toxic effects of the plant (Mitich, 1998). The specific name maculatum means spotted, from the characteristically spotted stem. Although a wide range of synonyms have been applied to C. maculatum, the original Linnean name is the only one to have been widely or consistently used, and there are no closely related species with which there is common confusion.

Following PIER, 2015 and Flora of China Editorial Committee, 2015:

C. maculatum is an erect annual or biennial, virtually glabrous, with a foetid, mousy odour when crushed. The long taproot is forked, white or pale yellow and 1-2 cm in diameter. Stems are hollow, striate, up to 2-(3) m high, usually light green and purple spotted or blotched, sometimes tinged purple-ish or pink, particularly toward their base. Leaves 2-4-pinnate; ultimate segments narrowly or broadly ovate to deltoid, pinnatisect or serrate, 5-40 mm long; petioles light green and purple blotched when mature; stem leaves similar to basal, but shortly petiolate and 1-3-pinnate. Umbels 1-8 cm in diameter; rays 4-16; lateral umbels overtopping the terminal; bracts c. > 4-8, narrow-triangular, acuminate, reflexed; bracteoles 3-6, triangular, confined to outer side of umbellets. Flowers numerous, white, c. 2 mm in diameter, hermaphrodite. Sepals 0, petals 5 notched at the broad tip. Fruit 2-seeded, dark brown, almost round, 2.5-3 mm long; slightly flattened, ribs slender, light brown, often crenulate.

The earliest specimens of C. maculatum in the USA date from the 1890s, while the first reports of its presence in Brazil and South Africa came from the 1920s, in New Zealand from 1865 (Thompson, 1922) and Australia from 1876 (Council of Heads of Australasian Herbaria, 2015). In Norway there is a report that its introduction dates from the early 1920s (Kielland-Lund and Often, 1998). In the latter instance it is believed to have been introduced accidentally with grain imports from the former USSR.

Soil drainage

• free
• impeded
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• heavy
• light
• medium

Special soil tolerances

• shallow

Natural Dispersal

Natural dispersal of C. maculatum is limited. It may be moved by water or wind but most seed falls close to the parent plant.

Vector Transmission (Biotic)

Some seed may cling to animal fur but there is no specialized mechanism for this. Mitich (1998) refers to spread by rodents and birds.

Accidental Introduction

Accidental introduction can occur locally through movement of garden waste, and more widely via contaminated seed of crops, but neither is likely to be frequent.

Intentional Introduction

Deliberate introduction is possible, where C. maculatum is considered a garden plant or used as a medicinal herb. However, it seems that the latter use is not common.

Significant damage may be caused by C. maculatum in establishing or established pastures, due to competition for light and other resources. Losses in other crops may occur locally, but are not widespread or severe and no crop loss data are available.

Indirect crop loss can occur as a result of the weed acting as an alternate host for: the carrot rust fly, Psila rosae (Distribution Maps of Plant Pests, 1957); Apium virus Y (Eastwell et al., 2008); carrot thin leaf virus, e.g. in California, USA (Howell and Mink, 1977); celery mosaic virus (Gracia and Feldman, 1977); and alfalfa mosaic virus (Fletcher, 2001). It can also host Xylella fastidiosa, a bacterium in the class Gammaproteobacteria, an important plant pathogen causing phony peach disease in southern USA (Cao et al., 2015).

The most important source of losses from C. maculatum is through toxicity to livestock. All parts of the plant are poisonous. Toxicity is due to a group of piperidine alkaloids of which the representative members are coniine and gamma-coniceine. The latter is the more toxic and is the first formed biosynthetically. Its levels in relation to coniine vary widely according to environmental conditions and to provenance of the plants (Reynolds, 2005).

Acute toxicity doses are 3.3 mg/kg for cattle, 15.5 mg/kg for horses and 44.0 mg/kg for sheep (CEH, 2004). Pigs are even more sensitive than cattle while goats are less sensitive than sheep (USDA, 2015). Mice given a fatal dose orally may die within 10 minutes. Poultry, pigs, hamsters, nutria and rabbits are also susceptible. Although birds can be poisoned, it appears that some at least are unharmed after eating the seeds. Their bodies are, however, then toxic to other animals including humans (The Poison Garden, 2015). C. maculatum may cause birth defects in farm animals (e.g. cleft palate, arthrogryposis, scoliosis, troticollis, kyphosis) (Panter and Keeler, 1993), in addition to acute toxicity.

The estimated economic loss of livestock due to poisonous weeds, including C. maculatum, in the seventeen western states of USA, was $340 million (N.B. based on prices and figures in 1989). This was estimated from a 1% death loss in cattle, a 3.5% death loss in sheep, and a 1% decrease in calf and lamb crops (James et al., 1992; Nielsen and James, 1992). We do not know, however, what proportion of those losses can be attributed to C. maculatum.

Livestock tend to avoid the fresh plant but do not recognise it in the dried state. This and other aspects of toxicity to livestock are well reviewed by Cao et al. (2015).

Impact on Habitats

Spread of C. maculatum into grassland or other low vegetation can significantly modify environments, and is of concern in conservation areas (Royal New Zealand Institute of Horticulture, 2015).

Impact on Biodiversity

C. maculatum can spread quickly in disturbed areas and is highly competitive, preventing the establishment of native grasses and forbs by shading and competing for space (Weber, 2003).

C. maculatum is dangerously poisonous and children have died from its toxicity. It is famously reputed to have been involved in the death of Socrates, though this is challenged by some, who find that the symptoms described do not adequately match those normally observed (Dayan, 2009).

Symptoms in humans include irritation and tachycardia leading to brachycardia, muscular paralysis and respiratory failure. Rhabdomyolysis and convulsions may also occur. Death can occur in two hours (Dauncey, 2010).

These symptoms reflect effects on the nervous system: stimulation followed by paralysis of motor nerve endings; and CNS stimulation followed by CNS depression. Other effects include vomiting, trembling, problems in movement, slow and weak pulse becoming rapid, rapid respiration, salivation, urination, nausea, convulsions, coma and death (Vetter, 2004). Advice on treatment following accidental ingestion is provided by Toxinz Poisons Information (2015).

Apart from the risks from ingestion, there is also a danger of significant effects from handling the plants without gloves, from breathing dust or pollen from the plant and from using the hollow stems as pea-shooters.

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Pioneering in disturbed areas
• Gregarious
• Has propagules that can remain viable for more than one year

• Modification of successional patterns
• Negatively impacts agriculture
• Negatively impacts human health
• Negatively impacts animal health
• Threat to/ loss of native species

• Competition - shading
• Competition - smothering
• Poisoning

Economic Value

Chemicals from C. maculatum have been shown to have plant protection properties. Young Chinese cabbage plants were sprayed with alkaloids from C. maculatum, including gamma-coniceine, and exposed to large numbers of starved slugs (Deroceras reticulatum). The alkaloids protected the plants over a 24-hour test period (Dodds and Henderson, 2002). Likewise, coniine from C. maculatum has proved effective against aphids and blowflies (Cao et al., 2015). Alinezhad et al. (2012) have demonstrated useful activity against Aspergillus parasiticus and a corresponding reduction in aflatoxin production. Extracts were shown to inhibit Fusarium pallidoroseum, the cause of twig blight in mulberry (Gulzar et al., 2013). However, it is unknown whether any of these ideas are being used in practice.

Social Benefit

As a medicine, C. maculatum is a sedative and antispasmodic. It is directly antagonistic to strychnine (a chemical used in pesticides), and has therefore historically been recommended as an antidote to strychnine poisoning; also in tetanus and hydrophobia (rabies). It may be prescribed as a remedy in cases of undue nervous motor excitability, such as teething in children, epilepsy from dentition, cramp, early stages of paralysis agitans (Parkinson’s disease), spasms of the larynx and gullet, acute mania, etc. As an inhalation it is said to relieve coughing in bronchitis, whooping-cough, asthma, etc. (Botanical.com, 2015). This site warns that many of these remedies date from early 20^th century and may no longer be approved, but a similar list is provided by other websites including WebMD (2015) and Mitich (1998), suggesting that they may still be practiced. In China, it may be used medicinally to relieve pain, and reputedly as a cancer cure (Flora of China Editorial Committee, 2015). Seeds of C. maculatum appear to be readily available for purchase on the internet, mostly with a warning of the potential hazards. It also seems to be recommended as a homeopathic remedy (for example, by Herbs2000.com [2015]) for a range of ailments.