Information Last Reviewed June 2007
Family: Asteraceae
Synonym: Centaurea repens
Symbol: ACRE3
Home Range/U.S. Introduction:
Russian knapweed, native to Eurasia, was introduced into North America in the late 1800's. Absent only from southeastern U.S., it has become widespread in other regions.
U.S. Range Map:
Species description:
Russian knapweed is a bushy rhizomatous perennial, up to 8 dm tall. Stems and leaves are finely arachnoid-tomentose becoming glabrous and green with age. The rosette leaves are oblanceolate, pinnately lobed to entire, 2-3 cm wide by 3-8 cm long. The lower cauline leaves are smaller, pinnately lobed; the upper leaves become much reduced, sessile, serrate to entire. The heads are numerous terminating the branches. Flowers are pink to purplish, the marginal ones not enlarged. The outer and middle involucral bracts are broad, striate, smooth with broadly rounded tips; the inner bracts are narrower with hairy tips. Pappus present with bristles 6-11 mm long. Fruit is a whitish, slightly ridged achene.
Growth Characteristics:
Russian knapweed is a deep-rooted long lived perennial. Some stands have been in existence for 75 years. It forms dense colonies in cultivated fields, orchards, pastures, and roadsides.
Problems:
The plant infests over 600,000 ha in nine western states and 2 Canadian provinces. It has recently become a problem in winter wheatlands. Once established, it is difficult to eradicate. It is poisonous to horses causing "chewing disease":.