Scientific Name: Centaurea stoebe ssp. micranthos

Common Name: spotted knapweed

Other Common Names: knapweed

Synonyms: Acosta maculosa, Centaurea biebersteinii, Centaurea maculosa

Habit: An erect growing biennial or short lived perennialthat grows to 1.2 m, is freely branching with rough hair (like sandpaper) and has purple to pink to white flowers.

Leaves: Produce rosette leaves in the first year that are composed of compound leaves with several irregularly lobed segments. The leaves of the second season are alternate, 5-15 cm long, moderately hairy with translucent dots covering the leaf surface. If basal leaves are present they are long stalked.

Identifying Characteristics: Has floral bracts, like leaves directly below the flower, that are black tipped, with purple to pink (sometimes white) flowers, and leaves are covered with translucent dots. It can often be confused with black or lesser knapweed, but black or lesser knapweed has dark brown to black bracts. It can also be confused with meadow knapweed, which has dark brown to tan bracts, corn cockle and cornflower. However, the flowering leaves of spotted knapweed are more lobed. Stems are wirey and has hairs.

Flower Seed Head: Has purplish to pink flowers that are 6-10 mm wide and 8-12 mm long. Flower heads are oval in shape before they open and occur at the end of the stalks. Bracts around the flower appear brown with black tips often.

Seed Fruit: Each floret produces a single seeded achene. Seeds are around 2 to 3 mm long, oblong, and grayish brown in color. Seed surfaces will have 10 to 15 faint ridges and several white hairs about 0.2 mm long.

Where Found: Found in the northeastern United States and along the pacific coast and as far east as Virginia. It is not a serious problem in cultivated crops; however, its early spring growth allows it to become a problem in pastures. This plant also produces a chemical that prevents other plants from growing in close proximity to it. This very competitive plant settles itself in any disturbed soil robbing other plants of moisture and nutrients.

  • Life cycle: perennial

  • Milky sap: Not Present

  • Plant type: Herb

  • Thorns: Not Present

  • Plant family: Asteraceae

  • Leaf arrangement: rosette; alternate

  • Leaf shape: lance; oval

  • Ochrea: Not Present

  • Leaf margin: lobed

  • Stem hairs: has hairs

  • Flower color: pink; purple

  • Growth habit: upright and nonwoody

  • Stem: round or oval; square or multi-edged

  • Leaf structure: simple; pinnate

  • Leaf hairs: has hairs

  • Flower diameter: dime; pencil

  • Flower symmetry: radial symetery

  • Root structure: taproot

  • Leaf stalk: shorter than leaf; none