Description and Variation:  Black knapweed has broadly lance-shaped basal leaves on a stalk. The leaves are toothed or shallowly lobed to entire. The stem leaves become smaller up the stem and are stalkless. The flowers are rose to lavender and bloom from July to October. Black knapweed is perennial from a woody root crown. The stems are erect, few, and branch near the middle or above and are eight to 32 inches tall. The bases of the stems are sometimes prostrate and rooting at several nodes. The seeds are about 1/8 inch long, ivory-white with lengthwise stripes; ring of hairs or plume pale colored, about 1/16 inch long. The broad comb-like bracts are roundish with dark brown or black fringed margins. The fringe length is up to three times as long as the width of the central part of the bract.

Economic Importance:  As with other knapweed species, black knapweed and the hybrid formed as a result of crosses between black and brown knapweed, have shown to be aggressive and invasive, particularly in pastures and meadows.

Geographical Distribution:  Black knapweed is native to western Europe (British Isles and western Norway) eastward to Sweden, and central Italy. Black knapweed has been collected occasionally in Washington since 1895.

Habitat:  Black knapweed appears to have become part of the meadow knapweed complex.

History:  Black knapweed has been introduced as a contaminant at seaports and by ornamental plantings. The earliest collection found is from Pullman, Washington, in 1895. It was collected on ballast ground near Portland from 1902 to 1916. Suksdorf grew it in his garden at Bingen, Washington, in 1928 (probably transplanted from ballast grounds). It was present at White River Camp on Mt. Rainier in 1925 (St. John and Warren 1937). It was also present in Quebec around 1850 (Rousseau 1968). Groh (1943) reports it as naturalized in eastern Canada.

Growth and Development:  Black knapweed is a perennial plant.

Reproduction:  Black knapweed reproduces by seeds and the woody root crown. It is a most tenacious weed that is spread rapidly by seed.

Response to Herbicides: Please refer to the recent Pacific Northwest Weed Control Handbook for more information. Read and follow current herbicide labels and recommendations for control.

Response to Cultural Methods:  Fire, tilling and seeding, mowing (clipping), fertilization, improved grazing systems, and combinations of those technologies can control black knapweed.

Biocontrol Potentials:  Predator insects and/or parasites

References:

Roche' Jr. Ben F., Extension Range Management Specialist; Gary L. Piper, Associate Professor of Entomology; and Cindy Jo Talbott, Extension Graduate Staff Assistant; WSU. Knapweeds of Washington. 1986. Washington State Cooperative Extension.

Scientific names follow Hitchcock C. Leo and Arthur Cronquist. 1976. Flora of the Pacific Northwest, with the following exceptions: Centaurea debeauxii, C. nigrescens, and C. trichocephala, described by J. Dostal. 1976. Flora Europaea. and C. amcrocephala by G. Wagenitz. 1975. Flora of Turkey.

The Collection History of Centaureas in Washington.

Moore and Frankton. 1974. The Thistles of Canada. Canada Dept. of Agriculture. Monograph No. 10.

Frankton and Mulligan. 1970. Weeds of Canada. Canada Dept. of Agriculture.