Quick Facts

Quick facts

• All parts of Hemlock (Conium maculatum) are poisonous to humans and livestock and will cause death by respiratory paralysis if eaten.
• A northern hemisphere bi-annual or sometimes annual herb to 2-2.5 m tall, green stems with light purple spots, large fern-like leaves, many small white cream or light pink flowers in compound umbels (umbrella-shaped groups) 30-70 mm in diameter at the end of stems, individual umbels with 10-20 flowers.
• Growing in cool to warm temperate climates in moist conditions, such as riverbanks, along roadsides and around the edges of pasture, in disturbed sites, mostly in shady situations.
• Spread by small 2.5-4 mm long seed and capable of rapid establishment and growth, seeds germinating in autumn and spring.
• Precludes the growth of other desired plants, and reduce the grazing value of and area.
• Requires a long-term management plan for successful eradication, with a combination of machine, manual and chemical treatment used to prevent seed set and exhaust the soil seed bank.

• Declared in NSW, Vic., and WA.

What Does It Look Like?

What is it?

Hemlock (Conium maculatum) is a robust, hairless, biennial or sometimes annual herb that grows up to 2.5 m high, reproducing (spreading) only by seed. The taproot is long and white. The light green stems are hollow, waxy-looking and spotted with purple to reddish brown blotches. The petiole (leaf stalk) is up to 600 mm long, longitudinally furrowed, and sheaths the plant stem. The leaf sheath and leaf stalk, and occasionally the main leaf stalk to the tip of the leaf, have purple to reddish brown blotches or flecks like the stem. The large leaves are arranged alternately, 300-500 mm long and deeply divided giving a fern-like appearance. The leaf outline is ovate (triangular in outline). When crushed the leaves give off an acrid smell.

The flowers are arranged in numerous (compound) umbels (umbrella-shaped groups) at the ends of the stems. Plants are capable of producing 100 or more flowering compound umbels at one time. Each compound umbel is 30-70 mm in diameter across, held on the main flowering stem (a peduncle). Each peduncle gives rise to 6-20 individual secondary flowering stems (also called secondary peduncles or rays), 1.5–3.5 cm long, on which individual umbels (also known as umbellets) are held. Each umbellet is about 8-15 mm in diameter across, with 10-20 small flowers, each held on a pedicel (individual flowering stalk) 2-5 mm long. Each flower is 2-4 mm in diameter, with petals 1-2 mm long, white, cream or rarely light pink, and sits on top of a small smooth ribbed ovary.

The small oval fruit, 2.5-4 mm long and 1.5-2 wide, has 10 well developed ribs. Fruit eventually falling from the plant when ripe (FloraVic 2016; Harden 2007; Parsons & Cuthbertson 2001; Walsh & Entwisle 1999). In favourable conditions each plant is capable of producing up to 40,000 seeds or more.

Recognition: This species can normally be recognised by the combination of the following characters; a large herb to 2.5 m tall; growing in seasonally moist to damp areas; soft green fern like leaves with acrid smell; many umbels of carrot like white, cream or rarely light pink flowers; and more importantly a green stem with purple blotches.

For further information and assistance with identification of Hemlock contact the herbarium in your state or territory.

Flower colour

White or cream or light pink

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Hemlock is a weed of neglected areas and disturbed sites, usually found in moist conditions, such as river banks and creeks, along roadsides, around the edges of pastures and in and near stockyards. It prefers shady situations (Parsons & Cuthbertson 2001; Harden 2007).

Are there similar species?

Wild Carrot (Daucus carota) has an absence of purple blotches on the stem,  and the stem is hairy, not smooth like hemlock, similar large leaves but the crushed leaves smell carroty. Although the white or pinkish flowers are in similar heads, the fruit has short spines, not smooth ridges.

Fennel (Foeniculum vulgare) has an absence of purple blotches on the stem, a similar habit but narrower leaf segments than Hemlock, and foliage that smells of aniseed when crushed, and yellow flowers, not white like hemlock.

Bishop's Weed (Ammi majus) has less divided leaves, solid stems, and an absence of spots on the stem.

The tall annual or biennial native herb (Trachymene anisocarpa) has similar branched umbrella-like heads of white flowers but its leaves tufted at the base of the plant and are less divided being composed of three lobed leaflets (Harden 2007; Miles undated).

Why Is It A Weed?

What are its impacts?

Hemlock is a significant weed because all parts of the plant are poisonous to humans and livestock. If eaten it will cause death by respiratory paralysis. The content of toxic alkaloids varies with climatic conditions and are presumed to be destroyed after heating. The seed and young plants are more toxic that other parts of the plant.

Agriculture: Cattle and pigs appear to be more susceptible than sheep and goats and young animals are more susceptible than old. Handling the plant may cause dermatitis in some people. Hemlock taints milk and can affect yield, and if consumed in sub-lethal doses, may cause birth deformities in unborn cattle and pigs. It is rarely eaten green by stock, but may be consumed when accidentally incorporated into hay or silage. Symptoms of poisoning in stock are loss of muscular power, stumbling and falling, salivation, nausea, dilation of pupils and convulsions. The symptoms usually occur within 1 hour of consuming the plant and death follows 2-3 hours later (Parsons & Cuthbertson 2001). Once established Hemlock can preclude the growth of other plants and reduce the grazing value of and area (Parsons & Cuthbertson 2001).

Native ecosystems: Hemlock is capable of rapidly establishing after rain particularly in disturbed or riparian sites or in areas where little vegetation occurs as a result of seasonal rainfall patterns, and can replace many native species. 

Urban areas: Hemlock will establish in urban riparian areas replacing desired species and can lead to human poisonings if consumed.

In humans it is capable of causing serious illness or death, and all parts of the plant are poisonous when ingested. Symptoms include nervousness, trembling and then respiratory distress. If poisoning occurs and:

• the patient is unconscious, unresponsive or having difficulty breathing dial 000 or get to the emergency section of a hospital immediately.
• the patient is conscious and responsive call the Poisons Information Centre on 13 11 26 or your doctor.
• If going to a hospital take a piece of the plant for identification.

How does it spread?

Hemlock is spread only by seed. Movement by natural means is via water, and seed may be spread over short distances by wind (Miles undated). It is also spread by people, sometimes great distances, via, farm or horticultural machinery or other vehicles, in contaminated soil (Parsons & Cuthbertson 2001), on clothing, or as a contaminant of farm produce, examples being hay or silage.

In Canada seed production may range from around 1,500 to 39,000 seeds per plant, about 80% of which are viable (Woodard 2008). However, in Australia plants produce a great abundance of compound umbels through the growing season and seed production could be greater than seen in Canada by Woodard (2008)

What is its history in Australia?

The timing of the introduction of Hemlock into Australia is uncertain. It was listed in nursery catalogues in Tasmania in 1845 and as a medicinal plant with commercial potential in the Victorian Royal Commission Report of 1871 (Parsons & Cuthbertson 2001). It was first collected in Tasmania in the Botanic Gardens in Hobart 1876, but it is unknown if this was a spontaneous weedy occurrence or a cultivated plant. The earliest known herbarium collections thought to be made from wild and weedy plants were collected from: NSW in1894; VIC in 1897; SA in 1917; ACT in 1935; QLD in 1947; WA in 1954 (AVH 2020).

How To Manage It?

Best practice management

Hemlock needs a long term management plan with different methods used in combination to achieve successful removal of an infestation (Williamson et al. 2007).

Chemical control: Chemical control should be carried out before flowering. Spot spraying is more effective than boom or mist spraying. Plants treated with some herbicides may become attractive to stock and special care should be taken to keep animals away from treated areas (Parsons & Cuthbertson 2001) as it is highly toxic to animals and humans and is capable of causing serious illness or death.

Non-chemical control: Physical control Individual plants of Hemlock should be hand pulled or hoed and large areas cultivated before plants flower. If pulling pants by hand gloves should be worn to protect against a reaction to the toxins in the plant. Follow up cultivation will be necessary to deal with seedlings. Mowing or slashing before flowering is useful but the bases of the plants may re sprout (Parsons & Cuthbertson 2001).

Competition and management: In grazed areas vigorous pasture should be sown to inhibit seedling growth. As Hemlock is highly toxic, capable of causing serious illness or death to all domestic animals (and humans), grazing should always be avoided. No biological control is available for Hemlock.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

The seed of Hemlock germinates mostly in autumn but occasionally also in spring. The seedlings grow rapidly developing a deep taproot in the first few months. Plants may produce flowers in the first spring after germination or may remain in the vegetative stage until flowering in the second spring. The plants die after flowering and seed production (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

ACT, NSW, QLD, SA, TAS, VIC, WA.

What areas within states and territories is it found?

Hemlock is present in the Australian Capital Territory. In New South Wales Hemlock is found in all coastal, tablelands and western slopes regions (Harden 2007). It is scattered in south-eastern Queensland. It is mainly found in eastern and southern Victoria with major infestations occurring around the urban areas of Melbourne, Geelong and Ballarat (Victorian Resources Online 2007). In Tasmania, it is found on the eastern and northern side of the island (AVH 2020). In South Australia, it is recorded in the cooler higher rainfall regions especially in the Adelaide Hill, the South East and Kangaroo Island, but also seems to be spreading in to moister areas of semi-arid dry parts of SA (eFlora of South Australia 2020). In Western Australia it grows in the south-west from Geraldton to Esperance, (Western Australian Herbarium).

Where does it originate?

Hemlock's original range is Europe, west Asia and north Africa. It has spread from these regions across most of the world as a garden and medicinal plant (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, VIC, WA.

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Conium maculatum L.

Other scientific names (synonyms)?

Does it have other known common name(s)?

Poison Hemlock, Spotted Hemlock, Wild Carrot Fern.