Conium maculatum
(poison hemlock)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Conium maculatum (poison hemlock); habit. Plants can reach 2m in height. Mexico. Copyright ©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US	Habit	Conium maculatum (poison hemlock); habit. Plants can reach 2m in height. Mexico.	©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US
Title Stem Caption Conium maculatum (poison hemlock); typical, 'purple' blotched stems. Mexico. Copyright ©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US	Stem	Conium maculatum (poison hemlock); typical, 'purple' blotched stems. Mexico.	©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US
Title Stem Caption Conium maculatum (poison hemlock); characteristic stem with purple blotching. Oregon, USA. June, 2005. Copyright ©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US	Stem	Conium maculatum (poison hemlock); characteristic stem with purple blotching. Oregon, USA. June, 2005.	©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Title Foliage Caption Conium maculatum (poison hemlock); foliage. Mexico. Copyright ©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US	Foliage	Conium maculatum (poison hemlock); foliage. Mexico.	©Pedro Tenorio-Lezama/Bugwood.org - CC BY-NC 3.0 US
Title Foliage Caption Conium maculatum (poison hemlock); foliage. Pándzsa-patak völgye, Pannonhalma, Hungary. Copyright ©Robert Vidéki/Doronicum Kft./Bugwood.org - CC BY-NC 3.0 US	Foliage	Conium maculatum (poison hemlock); foliage. Pándzsa-patak völgye, Pannonhalma, Hungary.	©Robert Vidéki/Doronicum Kft./Bugwood.org - CC BY-NC 3.0 US
Title Flowering habit Caption Conium maculatum (poison hemlock); flowering habit. Oregon, USA. June, 2005. Copyright ©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US	Flowering habit	Conium maculatum (poison hemlock); flowering habit. Oregon, USA. June, 2005.	©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Title Flowering umbel Caption Conium maculatum (poison hemlock); close-up of a flowering umbel. Oregon, USA. June, 2005. Copyright ©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US	Flowering umbel	Conium maculatum (poison hemlock); close-up of a flowering umbel. Oregon, USA. June, 2005.	©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Title Seeds Caption Conium maculatum (poison hemlock); seeds. USA. Copyright ©Steve Hurst/USDA NRCS PLANTS Database/Bugwood.org - CC BY-NC 3.0 US	Seeds	Conium maculatum (poison hemlock); seeds. USA.	©Steve Hurst/USDA NRCS PLANTS Database/Bugwood.org - CC BY-NC 3.0 US
Title Seedling Caption Conium maculatum (poison hemlock); seedling in laboratory conditions. USA. Copyright ©Ohio State Weed Lab Archive/The Ohio State University/Bugwood.org - CC BY-NC 3.0 US	Seedling	Conium maculatum (poison hemlock); seedling in laboratory conditions. USA.	©Ohio State Weed Lab Archive/The Ohio State University/Bugwood.org - CC BY-NC 3.0 US

Identity

Preferred Scientific Name

• Conium maculatum

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)

Summary of Invasiveness

C. maculatum is an herbaceous biennial and highly toxic plant, native across northern Europe, western Asia and North Africa. It has been introduced widely outside its native area to many parts of America, southern Africa, China, New Zealand and Australia. C. maculatum is a twofold invader, competing with pasture and crops and encroaching on native vegetation, while also posing a serious health hazard to virtually all livestock, and humans. Even within its native range, C. maculatum is increasing and tending to occur more commonly in crops.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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.

Description

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.

Plant Type

Distribution

Native across northern Europe, western Asia and N. Africa, C. maculatum has been introduced, deliberately or otherwise to many countries of America, to southern Africa and to China, New Zealand and Australia. Introduction to Micronesia is indicated by Weber (2003) and by USDA-ARS (2015) but no specimens are recorded by GBIF (2015), nor is it noted by the normally very comprehensive PIER (2015). Weber (2003) classes C. maculatum as invasive in Australia and western USA, while PIER (2015) additionally lists it as invasive in many Central and South American countries and the Chilean off-shore Juan Fernández Islands.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

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.

Introductions

Risk of Introduction

The risk of introduction is relatively low. The seed is conspicuous and, although possible, it is unlikely to be an undetected contaminant of any crop seed. Deliberate introduction as a garden plant or herbal medicine has occurred in the past but is less likely today.

Habitat

C. maculatum thrives in a number of habitats, including grassland, forest margins, riparian habitats, freshwater wetlands, waste ground, disturbed sites, field margins and fallows. In fallows, however, the infestations are relatively short-lived, persisting only 1-2 years (Németh, 2001).

This plant grows best in moist and fertile soils (Weber, 2003), avoiding acid soils and heavy shade (PFAF, 2015).

C. maculatum is thought to be more tolerant of soils containing heavy metals (arsenic, cadmium, lead) than some native species in USA, perhaps contributing to its competitive ability in such a situation (Gulezian et al., 2012).

In USA, C. maculatum is associated with USDA hardiness zones 4-8, so is tolerant of moderate to hard frosts. In Chile it may occur in USDA hardiness zone 9 where there may be dry periods of 3-5 months and where precipitation of 400-800 mm is concentrated in the winter. 

Habitat List

Hosts/Species Affected

Although growing mainly in non-crop areas, C. maculatum can invade field edges and encroach significantly on crops: maize in New Zealand; sugar beet in Slovakia and in France; pastures in Turkey, Poland, Australia and New Zealand; olive in Spain; lucerne (alfalfa) in USA; sunflower in Czech Republic; chickpea in Spain. Mitich (1998) refers to its occurrence in pastures, cereals, vegetable crops and orchards in many countries.

Host Plants and Other Plants Affected

Biology and Ecology

Genetics

A wide range of sources confirm C. maculatum to have a chromosome number of 2n = 22 (Missouri Botanical Garden, 2015).      

Reproductive Biology

The flowers of C. maculatum are hermaphrodite and pollinated by insects. The plant is self-fertile (PFAF, 2015). Seed production may range from around 1,500 to 39,000 seeds per plant, about 80% of which are viable (Woodard et al., 2008).

A detailed study by Baskin and Baskin (1990) concluded that in north-central Kentucky, USA, seeds of C. maculatum are dispersed from mid-September to mid-late February, with up to 95% of them being dispersed by late December. Depending on the year, 40-85% of the freshly matured seeds had morphological dormancy and thus only required a moist substrate for embryo growth and germination. The other seeds had morpho-physiological dormancy, which had to be broken before embryo growth and germination could occur. During late autumn and winter, a deeper form of dormancy was induced in most of the undispersed seeds. Germination was found to be higher on soil than on sand, and in light than in darkness.

DiTomaso et al. (2014) suggest that dormant seeds require high summer temperatures, low winter temperatures, or both, before they can germinate. Once seeds break dormancy, they can germinate from late summer to early spring, as long as temperatures remain cool and the soil remains moist. They found that C. maculatum does not require light for germination. However, Milanova et al. (2003) claimed that light was required for germination, but their results suggest that alternating temperatures of 25/30 degrees Celsius were a more important requirement. Germination was low at a constant 26⁰C in the light. Furthermore germination was not greatly reduced by burial below 5 cm depth.

Physiology and Phenology

Germination may occur in the autumn or the spring. After germination in spring it can flower and behave as an annual, but most plants behave as biennials, forming a low rosette of leaves before flowering in their second summer. Flowering occurs in mid-summer, while seed shed may continue through the autumn and winter to the following spring.

Longevity

The established plant does not normally persist for more than two summers. Seeds can persist in the soil for up to six years (Csontos, 2008).

Environmental Requirements

C. maculatum can occur across a wide range of soil types and levels of fertility. It is most commonly found, however, in moist conditions along rivers and in marshy ground. It can persist through relatively dry periods in the summer provided the winter is wet (Chileflora, 2006). It is stated to prefer high-nitrogen soils (Vetter 2004).

Climate

Latitude/Altitude Ranges

Rainfall

Rainfall Regime

Soil Tolerances

Soil drainage

• free
• impeded
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• heavy
• light
• medium

Special soil tolerances

• shallow

Natural enemies

Notes on Natural Enemies

Despite the high toxicity of C. maculatum to higher animals, and to some insects, many invertebrates appear to have evolved mechanisms for avoiding its toxicity (Castells and Berenbaum, 2008a; 2008b).

Goeden and Ricker (1982) observed that C. maculatum in California, USA, was attacked by fewer insects than many other introduced species. The most common insect associates were Hyadaphis foeniculi and Euscelidius variegatus, both accidentally introduced from Europe. Eighteen other species detected belonged to 6 orders and 13 families, and were represented by very few individuals. All 20 species were relatively unspecialized polyphagous ectophagous sap feeders or foliage feeders. The native Papilio zelicaon was apparently in the process of transferring to C. maculatum as a food-plant. In its native area, however, as in Hungary, C. maculatum may be host to a wide range of insects and fungi (Magyar and Tóth, 2003). The most interesting of these is the monophagous moth Agonopterix alstroemeriana which found its way from Europe to USA and to New Zealand in relatively recent years and has caused considerable damage.

A number of virus diseases occur naturally in C. maculatum, including carrot thin leaf, celery mosaic, alfalfa mosaic, ringspot and cucumber mosaic viruses (Fletcher, 2001). These do not kill the weed but may cause significant stunting.

Means of Movement and Dispersal

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.

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

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).

Environmental Impact

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).

Social Impact

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.

Risk and Impact Factors

• 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

Uses

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.

Uses List

Environmental

• Host of pest

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Similarities to Other Species/Conditions

C. maculatum is superficially similar to a number of other Apiaceae. Most dangerously it has been mistaken for wild carrot (Daucus carota), by children who have unwisely chewed on the yellowish root, but D. carota is clearly distinguished by having finely hairy foliage. Anthriscus sylvestris has similar foliage to C. maculatum but a hairy stem. The related and equally dangerous water hemlock, Cicuta maculata, has a glabrous hollow stem which may also be spotted, but the leaves have much wider segments and it has a cluster of fleshy roots and occurs in wetter situations. In general, C. maculatum is distinguished by its glabrous multi-pinnate leaves, the glabrous, hollow, spotted stem and mousy odour.

Prevention and Control

Prevention

SPS Measures

C. maculatum is a declared noxious weed in the following states of USA: Colorado, Idaho, Iowa, New Mexico, Nevada, Ohio, Oregon, Utah, Washington, West Virginia, Wyoming (USDA-ARS, 2015).

Control

Physical/Mechanical Control

Hand pulling of C. maculatum plants may be effective, especially prior to seed set. Spring mowing kills mature plants effectively, and a second mowing in late summer kills emerged seedlings and regrowth (Weber, 2003). It is warned that gloves should be used for any hand-pulling operation, and a mask if there is pollen or dry, powdery material to be handled.

Asav and Kadioglu (2008) demonstrated effective control of C. maculatum by solarisation in Turkey.

Biological Control

Agonopterix alstroemeriana (moth) has been introduced and spread naturally in the USA and New Zealand. The caterpillars of the moth can cause almost complete defoliation of the weed. Their use has been approved in USA for biological control and the moth has been utilized in eradication programmes (McKenna et al., 2001). Caterpillars are collected from infested areas and spread to where they are needed. Care is needed to avoid excessive contact with the weed, and gloves are advised.

Chemical Control

Glyphosate is effective, but control is influenced by the surfactant used in the formulation (Gonzalez-Gutierrez et al., 2000).

Other effective post-emergent herbicides include 2,4-D ester, 2,4-D amine, dicamba and triclopyr (Weber, 2003). Effective pre-emergence herbicides include imazapyr, tebuthiuron, chlorsulfuron, metsulfuron, hexazinone, metribuzin, terbacil, aminopyralid.

Herbicides for specific crops include pyridate and propaquizafop in chickpea; clopyralid in rapeseed; hexazinone, metribuzin and terbacil in lucerne/alfalfa. In clover-based pastures, flumetsulam or bentazone were better than 2,4-DB (Gawn et al., 2012).

IPM Programmes

The following guidance is provided by Panter et al. (2002):

‘Basic management recommendations to reduce reproductive losses to poisonous plants include: (1) keep good records; (2) know what poisonous plants grow on ranges and understand their effects; (3) develop a management plan to provide for alternate grazing in poisonous plant-free pastures during critical times; (4) provide for balanced nutrition, including protein, energy, minerals and vitamins; (5) maintain a good herd health program; (6) integrate a herbicide treatment programme to reduce poisonous plant populations or to maintain clean pastures for alternate grazing; and (7) manage the range for maximum forage production.’

References

Alinezhad S; Kamalzadeh A; Rezaee MB; Jaimand K; Shams-Ghahfarokhi M; Razzaghi-Abyaneh M, 2012. Inhibitory effects of some native medicinal plants on Aspergillus parasiticus growth and aflatoxin production. Acta Horticulturae [I International Symposium on Mycotoxins in Nuts and Dried Fruits, Damghan, Iran], 963:207-210.

Asav Ü; Kadioglu I, 2008. Effects of soil solarization and poultry manure combinations on seed germination of some weed species. (Toprak solarizasyonu ile tavuk gübresigt; kombinasyonunun bazi yabanci ot tohumlarinin çimlenmelerine etkileri). Türkiye Herboloji Dergisi, 12(2):11-22.

Baskin JM; Baskin CC, 1990. Seed germination ecology of poison hemlock, Conium maculatum. Canadian Journal of Botany, 68(9):2018-2024.

Botanical.com, 2015. Hemlock. Electronic version of "A Modern Herbal" by Mrs M. Grieve. http://www.botanical.com/botanical/mgmh/h/hemloc18.html

Cao L; Larson J; Berent L; Fusaro A, 2015. Nonindigenous Aquatic Species Database: Conium maculatum. Gainesville, Florida, USA: US Geological Survey.

Castells E; Berenbaum MR, 2008a. Resistance of the generalist moth Trichoplusia ni (Noctuidae) to a novel chemical defense in the invasive plant Conium maculatum. Chemoecology, 18(1):11-18.

Castells E; Berenbaum MR, 2008b. Host plant selection by a monophagous herbivore is not mediated by quantitative changes in unique plant chemistry: Agonopterix alstroemeriana and Conium maculatum. Arthropod - Plant Interactions, 2(1):43-51.

CEH, 2004. Information sheet 15: Poison-hemlock. Wallingford, UK: Centre for Ecology and Hydrology, 3 pp. http://www.ceh.ac.uk/sci_programmes/documents/poison_hemlock.pdf

Chileflora, 2006. Conium maculatum L. Talca, Chile: Chileflora. http://www.chileflora.com/Florachilena/FloraEnglish/HighResPages/EH0528.htm

Council of Heads of Australasian Herbaria, 2015. Australia's virtual herbarium. Australia: Council of Heads of Australasian Herbaria. http://avh.ala.org.au/#tab_simpleSearch

Csontos P, 2008. Longevity of Conium maculatum L. achenes in a 6-year-long seed burial experiment. (A bürök (Conium maculatum L.) terméseinek túlélése a talajban). Növényvédelem, 44(9):441-443.

Dauncey EA, 2010. Poisonous plants: a guide for parents and childcare providers. Richmond, UK: Royal Botanic Gardens Kew, 180 pp.

Dayan AD, 2009. What killed Socrates? Toxicological considerations and questions. Postgraduate Medical Journal, 85(999):34-37.

Distribution Maps of Plant Pests, 1957. Psila rosae [Distribution map 84]. Wallingford, UK: CAB International.

DiTomaso JM; Roncoroni JA; Swain SV; Wright SD, 2014. Pest notes: poison hemlock. Davis, California, USA: Statewide IPM Program, Agriculture and Natural Resources, University of California. [UC ANR Publication 74162.] http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74162.html

Dodds CJ; Henderson IF, 2002. Control of slug and snail damage using low toxicity, plant-derived repellents and antifeedants. HGCA Project Report, No.294:49 pp.

Eastwell KC; Glass JR; Seymour LM; Druffel KJ, 2008. First report of infection of poison hemlock and celery by Apium virus Y in Washington State. Plant Disease, 92(12):1710.

Fletcher JD, 2001. New hosts of alfalfa mosaic virus, cucumber mosaic virus, potato virus Y, soybean dwarf virus, and tomato spotted wilt virus in New Zealand. New Zealand Journal of Crop and Horticultural Science, 29(3):213-217.

Fletcher JD, 2001. New hosts of alfalfa mosaic virus, cucumber mosaic virus, potato virus Y, soybean dwarf virus, and tomato spotted wilt virus in New Zealand. New Zealand Journal of Crop and Horticultural Science, 29(3):213-217.

Flora of China Editorial Committee, 2015. Flora of China. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria. http://www.efloras.org/flora_page.aspx?flora_id=2

Gawn TL; Harrington KC; Matthew C, 2012. Weed control in establishing mixed swards of clover, plantain and chicory. New Zealand Plant Protection [New Zealand Plant Protection Society's Annual Conference, Rutherford Hotel, Nelson, New Zealand, 14-16 August 2012.], 65:59-63. http://www.nzpps.org/journal/65/nzpp_650590.pdf

GBIF, 2015. Global Biodiversity Information Facility. http://www.gbif.org/species

Goeden RD; Ricker DW, 1982. Poison hemlock, Conium maculatum, in southern California - an alien weed attacked by few insects. Annals of the Entomological Society of America, 75(2):173-176.

Gonzalez-Gutierrez J; Osuna MD; de Prado R, 2000. Behaviour of glyphosate in Conium maculatum control. Mededelingen - Faculteit Landbouwkundige en Toegepaste Biologische Wetenschappen, Universiteit Gent [Proceedings, 52nd International Symposium on Crop Protection, Gent, Belgium, 9 May 2000, Part I.], 65(2a):157-160.

Gracia O; Feldman JM, 1977. Isolation and identification of two celery viruses in Argentina. Plant Disease Reporter, 61(11):905-908.

Gulezian PZ; Ison JL; Granberg KJ, 2012. Establishment of an invasive plant species (Conium maculatum) in contaminated roadside soil in Cook County, Illinois. American Midland Naturalist, 168(2):375-395.

Gulzar P; Kausar T; Sahaf KA; Munshi NA; Ahmad S; Raja TA, 2013. Screening of ethanolic extracts of various botanicals against Fusarium pallidoroseum (Cooke) Sacc. - the causal agent of twig blight of mulberry. Indian Journal of Sericulture, 52(1):24-28.

Herbs2000.com, 2015. Homeopathy - Conium maculatum. Herbs2000.com. http://www.herbs2000.com/homeopathy/conium.htm

Howell WE; Mink GI, 1977. The role of weed hosts, volunteer carrots, and overlapping growing seasons in the epidemiology of carrot thin leaf and carrot motley dwarf viruses in central Washington. Plant Disease Reporter, 61(3):217-222.

James LF; Nielsen DB; Panter KE, 1992. Impact of poisonous plants on the livestock industry. Journal of Range Management, 45(1):3-8.

Kielland-Lund J; Often A, 1998. Conium maculatum in Hedmark county, eastern Norway. (Giftkjeks Conium maculatum pa Hedemarken.) Blyttia, 56(2):92-93.

Lorenzi H, 1982. Plantas Daninhas do Brasil. Nova Odessa, San Paulo, Brazil: H. Lorenzi.

Magyar D; Tóth S, 2003. Data to the knowledge of the microscopic fungi in the forests around Budakeszi (Buda Hills, Hungary). Acta Phytopathologica et Entomologica Hungarica, 38(1/2):61-72.

McKenna DD; Zangerl AR; Berenbaum MR, 2001. A native Hymenopteran predator of Agonopterix alstroemeriana (Lepidoptera: Oecophoridae) in east-central Illinois. Great Lakes Entomologist, 34(1):71-75.

Milanova SD; Nikolova V; Maneva S, 2003. Some morphological and bioecological characteristics of Conium maculatum L. In: Uygur S, Kolören O, eds. Proceedings of the 7th EWRS (European Weed Research Society) Mediterranean Symposium. Doorwerth, Netherlands: European Weed Research Society, 161-162.

Missouri Botanical Garden, 2015. Tropicos database. St. Louis, Missouri, USA: Missouri Botanical Garden. http://www.tropicos.org/

Mitich LW, 1998. Poison-hemlock (Conium maculatum L.). Weed Technology, 12(1):194-197.

Nemeth I, 2001. Weed flora of fields set-aside for a long period in Northern Hungary. Novenytermeles, 50(2/3):217-230.

Nielsen DB; James LF, 1992. Economic impact of poisonous plants on livestock production. In: James LF, Keeler RF, Bailey EM, Cheeke PR, Hegarty MP, eds. Poisonous plants: Proceedings of the Third International Symposium. Ames, USA: Iowa State University Press, 3-10.

Panter KE; James LF; Gardner DR; Ralphs MH; Pfister JA; Stegelmeier BL; Lee ST, 2002. Reproductive losses to poisonous plants: influence of management strategies. Journal of Range Management, 55(3):301-308.

Panter KE; Keeler RF, 1993. Quinolizidine and piperidine alkaloid teratogens from poisonous plants and their mechanism of action in animals. Veterinary Clinics of North America, Food Animal Practice, 9(1):33-40.

Parsons WT; Cuthbertson EG, 1992. Noxious Weeds of Australia. Melbourne, Australia: Inkata Press, 692 pp.

PFAF, 2015. Conium maculatum L. Plants for a future. http://www.pfaf.org/user/Plant.aspx?LatinName=Conium+maculatum

PIER, 2015. Pacific Islands Ecosystems at Risk. Honolulu, USA: HEAR, University of Hawaii. http://www.hear.org/pier/index.html

Reynolds T, 2005. Hemlock alkaloids from Socrates to poison aloes. Phytochemistry, 66(12):1399-1406.

Royal New Zealand Institute of Horticulture, 2015. Conium maculatum: hemlock. In: Popay I, Champion P, James T, eds. An illustrated guide to common weeds of New Zealand (reproduced online version). Canterbury, New Zealand: New Zealand Plant Protection Society. http://www.rnzih.org.nz/pages/coniummaculatum.htm

The Poison Garden, 2015. Conium maculatum, poison hemlock. Alnwick, UK: The Poison Garden. http://www.thepoisongarden.co.uk/atoz/conium_maculatum.htm

Thompson GM, 1922. The naturalisation of animals and plants in New Zealand. London, UK: Cambridge University Press, 607 pp.

Toxinz Poisons Information, 2015. Conium maculatum. Dunedin, New Zealand: National Poisons Centre. http://www.toxinz.com/Demo/11/UExIMDIyLzEwNGg%3D

USDA, 2015. Field guide for managing poison hemlock in the Southwest. Washington DC, USA: US Department of Agriculture, 12 pp. http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5410121.pdf

USDA-ARS, 2015. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx

USDA-NRCS, 2015. The PLANTS Database. Baton Rouge, USA: National Plant Data Center. http://plants.usda.gov/

Venclová V; Neckár K; Brant V, 2007. The influence of field border plant communities on the occurrence of Conium maculatum (L.) in agrophytocoenoses. In: Floistad E, ed. European Weed Research Society, 14th EWRS Symposium, Hamar, Norway, 17-21 June 2007. Doorwerth, Netherlands: European Weed Research Society, 227.

Vetter J, 2004. Poison hemlock (Conium maculatum L.). Food and Chemical Toxicology, 42(9):1373-1382.

Webb CJ; Sykes WR; Garnock-Jones PJ, 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Christchurch, New Zealand: Botany Division, DSIR, 1365 pp.

Weber E, 2003. Invasive plant species of the world: A reference guide to environmental weeds. Wallingford, UK: CAB International, 548 pp.

WebMD, 2015. Find a vitamin or supplement - Hemlock. New York, USA: WebMD. http://www.webmd.com/vitamins-supplements/ingredientmono-949-hemlock.aspx?activeingredientid=949&activeingredientname=hemlock

Woodard CA, 2008. Poison hemlock (Conium maculatum L.): biology, implications for pastures and response to herbicides. MS Thesis. Columbia, USA: University of Missouri, 80 pp.

Wunderlin RP; Hansen BF, 2008. Atlas of Florida Vascular Plants. Tampa, Florida, USA: University of South Florida. http://www.plantatlas.usf.edu/

Contributors

25/3/15 Original text by: 

Chris Parker. Consultant, Bristol, UK

Distribution Maps