Weed Seed: Heracleum mantegazzianum (Giant hogweed)

Family

Apiaceae

Common Name

Giant hogweed

Regulation

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

Distribution

Canadian: Occurs in BC, ON, QC, NB, NL, NS (Page et al. 2006^Footnote 1).

Worldwide: Native to the Caucasus region of Asia (Georgia, Russia) and introduced in Europe, North America, Australia and New Zealand (USDA-ARS 2016^Footnote 2).

Duration of Life Cycle

Monocarpic perennial (dies after flowering)

Seed or fruit type

Schizocarp, divided into 2 mericarps

Identification features

Size

Mericarp length: 6.0 - 18.0 mm
Mericarp width: 4.0 - 10.0 mm

Shape

Long oval-shaped mericarp, flattened

Surface Texture

Mericarp smooth, dull

Colour

Mericarp straw yellow with reddish oil ducts

Other Features

Teeth along the edge, especially near the top of the mericarp
The oil ducts extend 3/4 down the mericarp and have enlarged ends
The ventral side of the style remnant at the top of the mericarp is M-shaped

Habitat and Crop Association

Fields, gardens, pastures, grasslands, open forests, forest edges, forested floodplains, shorelines, ditches, landfills, gravel bars, roadsides and urban parks (Darbyshire 2003^Footnote 3, Page et al. 2006^Footnote 1). Not a common agricultural weed (Page et al. 2006^Footnote 1).

General Information

Giant hogweed was planted in European botanical gardens of the early 19th century as an ornamental and was first recorded in Canada in 1949 in Ontario (Page et al. 2006^Footnote 1). It favours regions with cool, moist climates and soils with high organic matter (Page et al. 2006^Footnote 1, CABI 2016^Footnote 4).

Similar Species

Cow parsnip (Heracleum sphondylium subsp. montanum)

Cow parsnip mericarps are similar size, oval shape, reddish oil ducts and straw yellow colour as giant hogweed.
Cow parsnip mericarps have an arrow shape on the ventral side of the style remnant, no teeth on the margin, and have thinner oil ducts compared to giant hogweed.