Weed Seed: Conium maculatum (Poison hemlock)

Family

Apiaceae

Common Name

Poison hemlock

Regulation

Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs in AB, BC, NB, NS, ON, QC, SK (Brouillet et al. 2016^Footnote 1).

Worldwide: Native to northern Africa, Europe and western and central Asia. Introduced to North and South America, southern Africa, Australia, New Zealand and Micronesia (USDA-ARS 2016^Footnote 2).

Duration of life cycle

Biennial

Seed or fruit type

Schizocarp, divided into 2 mericarps

Identification features

Size

• Mericarp length: 2.0 - 4.0 mm
• Mericarp width: 1.5 - 2.5 mm
• Mericarp thickness 1.3 - 2.0 mm

Shape

• Oval to teardrop-shaped mericarp, flat on the ventral side

Surface Texture

• Mericarp dull surface, wrinkled between the wavy ribs

Colour

• Mericarp greyish-brown to brown with straw-yellow ribs

Other Features

• Musty smell if mericarp surface is punctured
• Five ribs on the dorsal side; no ribs on the ventral side of the mericarp

Habitat and Crop Association

Cultivated fields, pastures, roads and disturbed areas (Darbyshire 2003^Footnote 3, CABI 2016^Footnote 4). Invades a variety of crops, including cereal and vegetable crops, as well as orchards, often by encroachment from field edges (CABI 2016^Footnote 4).

General Information

Poison hemlock was brought to the United States as a garden plant in the 19th century (DiTomaso and Healy 2007^Footnote 5). Seed may have spread by mud, boots and other human clothing, as well as by machinery and transported soil (Ministry of Agriculture, Food, and Fisheries 2002^Footnote 6).

Poison hemlock grows in lowlands on dry to moist soils and can tolerate poorly drained soils (Ministry of Agriculture, Food, and Fisheries 2002^Footnote 6). It is poisonous to livestock (CABI 2016^Footnote 4).

Similar species

Wild carrot (Daucus carota subsp. carota)

• The mericarps of wild carrot and poison hemlock are a similar size, oval - teardrop shape and grey-brown colour.
• Wild carrot mericarps may lack their typical long wings and hairs if processed, immature or damaged.
• Wild carrot mericarps may still retain small hairs on the straight ribs, the surface between the ribs is smooth, and thin ribs are on the ventral side. Poison hemlock does not have hairs, ribs are wavy and the surface is wrinkled. The ventral side of the mericarp does not have ribs.

Photos

Similar species