Meadow knapweed, from Europe, is a hybrid of black and brown knapweeds. It is well adapted to western Washington, where it invades pastures, parks, lawns, industrial sites, tree farms, vacant lands, railroads and roadsides. Its foliage is coarse and tough and not generally palatable to livestock. Meadow knapweed out-competes grasses and other pasture species and is difficult to control. It threatens wildlife habitat and causes problems for Christmas tree growers. Knapweed invasions cause losses averaging up to 63 percent of available grazing forage. Meadow knapweed is also known as Centaurea pratensis, Centaurea × moncktonii and Centaurea debeauxii subsp. thuillieri.
Centaurea jacea x nigra
Legal status in King County, Washington
Class B noxious weed. Property owners in King County are required to control this plant. This species is also on the Washington quarantine list (known as the prohibited plants list) (external link) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts, seeds in packets, blends or "wildflower mixes" of this species, into or within the state of Washington.
Biology and morphology
Meadow knapweed favors moist roadsides, sand/gravel bars and river banks, irrigated pastures, moist meadows, and forest openings. It is a perennial of the sunflower family (Asteraceae) and grows from a woody crown. Upright stems branch near the middle, with leaves up to6 inches long by more than an inch wide. The lower leaves are lobed or toothed; middle and upper leaves are linear. In King County it flowers from late May to August, later if it is mowed. Its flower heads are solitary at tips of the branches. Each is about the size of a nickel, pink to purple, and much rounder than spotted knapweed heads. Bracts around the flower head are light to dark brown, with paper-fringed margin, and appear shiny and coppery when flowers are mature. Seeds are about 1/8 inch long, ivory to light brown. A short row of hairs may be present on one end.
Additional information on meadow knapweed
What to do if you find this plant in King County, Washington
Please notify us if you see meadow knapweed growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. We map all known locations of regulated noxious weeds such as meadow knapweed in order to help us and others locate new infestations in time to control them.
Meadow knapweed photos - click thumbnail for larger image