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Last Updated: Spring 2011
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Synonyms: *Note: According to the latest version of the USDA Plants Database, this plant has been renamed to Centaurea stoebe L.

Family: Asteraceae

Home Range/U.S. Introduction:
Spotted knapweed was introduced from Eastern Europe in the early 1900's as a contaminant in crop seed. It has become widespread in northern and western U.S. and in Canada.

U.S. Range Map:

Species Description:
Spotted knapweed is a biennial or short lived perennial with a stout taproot. The plant grows 3-12 dm tall having multiple branching stems that are smooth to scabrous. The leaves are pinnatifid with narrow lobes, scabrous puberulent and usually arachnoid-tomentose. Upper leaves may become linear and entire. The pink to light purple flowers are in solitary heads terminating the branches. The involucral bracts are stiff, striate; the outer and middle ones having short dark pectinate tips. Pappus up to 3 mm long. The fruit is a brown or blackish achene with longitudinal lines, glabrous or sparsely pilose.

Habitat/Growth Characteristics:
Spotted knapweed is an aggressive plant that rapidly invades pastures, rangeland, dry meadows, flood plains, roadsides and any other dry, gravelly or sandy sites. Early spring growth make knapweeds very competitive for soil moisture and nutrients.

Seeds are produced prolifically and remain viable for a number of years. Infestations crowd out desirable native vegetation. Rangelands are severely impacted because grazing animals pass over knapweed in favor of native grasses and herbs. Hence it is the number one rangeland weed in Montana.