Spotted Knapweed
Centaurea stoebe
Asteraceae
(Sunflower family)

Spotted knapweed, which was introduced from Eurasia as a contaminant of alfalfa and clover seed, ranks as the No. 1 weed problem on rangeland in Western Montana. Other Western states are experiencing a reduction in desirable plant communities as the species spreads.

Growth Habit: Biennial or short lived perennial, up to 3 feet tall. Rosette formed first year, flowering stalk elongates second year.

Leaves: Long and divided below, short and narrow above. Covered with fine hair.

Flowers: Seed heads mostly on branch tips, solitary, to 1 inch diameter. Pink to purple, rarely white. Seed head bracts underneath the flowers are black tipped, giving them a spotted appearance. Flowers from June to October.

Roots: Taproot, not well developed.

Other: Very aggressive, can infest large areas quickly, offers very little big game or livestock forage value. Also, since spotted knapweed does not hold soil nearly as well as native vegetation, erosion increases dramatically where knapweed dominates.