Weed Seed: Rhaponticum repens (Russian knapweed)
Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.
Canadian: Occurs in AB, BC, MB, ON, SK (Brouillet et al. 2016Footnote 1).
Worldwide: Native to eastern Europe and temperate Asia and introduced in North America, Argentina, Australia, and beyond its native range in Europe (USDA-ARS 2016Footnote 2).
Duration of life cycle
Seed or fruit type
- Achene length: 2.5 - 4.0 mm
- Achene width: 1.5 - 2.5 mm
- Obovate-shaped achene, compressed
- Achene has shallow longitudinal ridges
- Achene is bone-white to pale straw colour
- Pappus present only on immature achenes
- Small (0.5 mm) notch at or near the base of the achene
- Short peg at the top of the achene
Habitat and Crop Association
Cultivated fields, old fields, pastures, rangelands, ditches, roadsides, railway lines and disturbed areas (Watson 1980Footnote 3, Darbyshire 2003Footnote 4). Reported as a weed of alfalfa (Watson 1980Footnote 3).
Russian knapweed was introduced into Canada in the early 1900s as a contaminant in alfalfa seed (Watson 1980Footnote 3). This species is found on a variety of soil types, and has been noted to invade areas where it was not directly introduced (Watson 1980Footnote 3).
Russian knapweed seed can persist in the soil for up to 75 years, and the plants also readily reproduce through stem buds borne on the roots (Watson 1980Footnote 3). A dense patch of plants can spread up to 12 square metres in 2 years (Watson 1980Footnote 3). Leaves and stems are also reported to be toxic to horses (Watson 1980Footnote 3).
Gumweed (Grindelia squarrosa)
- Gumweed achenes may be similar obovate size, longitudinal ribs and pale colour as Russian knapweed.
- Gumweed achenes are more angular-shaped than Russian knapweed, and do not have a notch at the base of the achene. Gumweed also lacks a pappus.
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