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Diffuse Knapweed Centaurea diffusa


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Diffuse Knapweed
© Cindy Roche/

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Family: Asteraceae, Aster view all from this family

Description Introduced. A weedy, much-branched and wide-spreading, upright plant that is not native to North America and widely considered a noxious weed.
Flowers: rayless, thistle-like, cream to pink or purple flower heads at ends of branches, usually solitary, subtended by weakly spiny, overlapping bracts.
Leaves: lower leaves large and divided, upper leaves smaller and less lobed.
Height: 8-36" (20-90 cm).

Habitat Disturbed areas, rangelands, dry open woodlands, watercourses, roadsides.

Range Native of Mediterranean Asia and eastern Europe; introduced and naturalized in North America, especially the West and Midwest.

Discussion Diffuse Knapweed can quickly colonize an area to the exclusion of all other plants. It is thought to do this by an ability to outcompete other plants for soil moisture, and by exuding toxins that make the soil inhospitable to other plants. The large, branched top part of the plant snaps off when dry and blows along like tumbleweed, dispersing seeds.