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Hardheads Acroptilon repens (Centaurea repens)


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© Norman E. Rees, USDA ARS/

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Alternate name: Russian Knapweed

Family: Asteraceae, Aster view all from this family

Description Introduced. An invasive, much-branched, upright-growing weed that spreads by black creeping roots.
Flowers: scaled buds open to reveal whitish to rose-pink, thistle-like flower heads at the tips of stems.
Leaves: variable, copious, gray-green; stem leaves small, narrow, toothed.
Height: 1-3' (30-90 cm).

Warning Plant parts are reported to be poisonous to horses when eaten. Humans should avoid consuming plants that are toxic to animals.

Flower May-September.

Habitat Grasslands, agricultural fields, scrub or shrub habitats, riverside communities, roadsides, ditches, and other disturbed habitats.

Range Asia native; naturalized in North America from the West Coast eastward to Manitoba, Ohio, Kentucky, Arkansas, and Texas; recently reported in Virginia.

Discussion Accidentally introduced to the United States as a contaminant in crop seed, Hardheads, or Russian Knapweed, is classified as a noxious weed in dozens of states and four Canadian provinces. Budding root systems enable this plant to spread rapidly; toxic compounds exuded by the plant make the soil inhospitable for other plants. It is thus able to infiltrate natural habitats and outcompete native flora.