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Weed Seed: Centaurea virgata subsp. squarrosa (Squarrose knapweed)

Family

Asteraceae

Common Name

Squarrose knapweed

Regulation

Prohibited Noxious, Class 1 in the Canadian Weed Seeds Order, 2016 under the Seeds Act. All imported and domestic seed must be free of Prohibited Noxious weed seeds.

Distribution

Canadian: Absent from Canada (Brouillet et al. 2016Footnote 1).

Worldwide: Native to temperate Asia and introduced in the western United States and Michigan (USDA-ARS 2016Footnote 2, DiTomaso and Healy 2007Footnote 3).

Duration of life cycle

Perennial

Seed or fruit type

Achene

Identification features

Size

Shape

Surface Texture

Colour

Other Features

Habitat and Crop Association

Degraded rangelands, grasslands, open sites, logged areas, and roadsides (Cal-IPC 2016Footnote 4).

General Information

Squarrose knapweed was accidently introduced into California in 1930s with sheep ranching (Howell 1959Footnote 5). This species tolerates a wide range of temperatures and drought conditions, but does not tolerate cultivation or irrigation (Whitson et al. 1996Footnote 6).

Similar species

Spotted knapweed (Centaurea stoebe)

Photos

Figure 1 - Squarrose knapweed (Centaurea virgata subsp. squarrosa) achenes
Squarrose knapweed (Centaurea virgata subsp. squarrosa) achenes
Figure 2 - Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene, side view
Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene, side view
Figure 3 - Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene
Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene
Figure 4 - Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene, basal notch
Squarrose knapweed (Centaurea virgata subsp. squarrosa) achene, basal notch

Similar species

Figure 5 - Similar species: Spotted knapweed (Centurea stoebe) achene
Similar species: Spotted knapweed (Centurea stoebe) achene
Figure 6 - Similar species: Spotted knapweed (Centurea stoebe) achenes
Similar species: Spotted knapweed (Centurea stoebe) achenes
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