[Cal-IPC] Invasive: Centaurea jacea ssp. pratensis (=Centaurea debeauxii or C. jacea x C. nigra or C. x pratensis) (meadow knapweed) is a bushy perennial (family Asteraceae) found in a small number of disturbed areas in Siskiyou, Del Norte, and Humboldt Counties in northwestern California. Meadow knapweed reproduces by seed and via shoots from the parent plant, and is known to resprout from root fragments after cultivation. The seeds can also be spread by irrigation systems and vehicles. Meadow knapweed spreads very rapidly and is listed as a noxious weed in several western states as well as California. Cal-IPC Rating: Moderate Alert (contributed by Mary Ann Machi)

[www.mda.state.mn.us] European native, Description: Meadow knapweed is native to Europe and is likely a fertile hybrid between black (C. nigra L.) and brown (C. jacea L.) knapweeds. It may have been introduced to western North America for forage, but it is not palatable and has low nutritional value. Meadow knapweed escaped cultivation and is proliferating rapidly in the Pacific Northwest.

Description: Meadow knapweed is a perennial plant that has multiple upright, reddish stems with vertical ridges that are 20 to 40" tall. Single flowers, mostly pink/purple but occasionally white, are at the ends of branches and are approximately ¾" in diameter. Flowering occurs mid-summer until fall, followed by the production of white to light brown seeds with short plumes. Leaves are lance-shaped and pubescent, occasionally with wavy margins or lobed. Basal leaves grow 4 to 9" long. Seedlings are tap-rooted and mature plants develop a cluster of roots below the crown. Flower buds and young leaves have a cobwebby appearance. (contributed by Mary Ann Machi)