Synonyms:

• Centaurea biebersteinii, C. maculosa, Acosta maculosa

The Plant:

• A biennial or short-lived perennial, 1-3 feet tall, with a stout taproot. Slightly pubescent, with one or more branched upright stems.

The Leaves:

• basal
• up to 6 inches long
• blades narrowly elliptic to oblanceolate
• entire to pinnately parted
• stem leaves pinnately divided

The Stem:

• multi-branched
• thin
• wiry
• coarse

The Flowers:

• Thistle-like flowering heads with many petals. The ray flowers are pinkish purple, seldom cream colored. The involucral bracts are stiff and tipped with a dark, comb-like fringe. Blooms from June to October.

The Fruits:

• brown and dry, 1/8 inch long
• tipped with a tuft of persistent bristles

The Habitat:

• dry, gravelly sites
• waste places, disturbed soils, roadsides

Dispersal:

• stick to animals and humans
• wind
• contaminated hay
• can resprout from lateral root buds or from crown of leaves, especially following attempts at removal

Key ID Features:

• thistle-like, pinkish-purple flowers
• stiff bracts
• fruit topped with bristles
• wispy foliage

Similar Species:

• Russian knapweed (Centaurea repens), Cornflower (C. cyanus), Diffuse knapweed (C. diffusa), Black knapweed (C. nigra), and Brown knapweed (C. jacea) all have similar inflorescences
• Other knapweeds lack the black-tipped flower bracts that are characteristic of this species.

Notes:

• Spotted knapweed can invade and seriously effect the biodiversity of an area, by choking out native vegetation. Erosion occurs due to its inability to hold the soil. Hand-pulling, cutting or mowing over several years may successfully eliminate Spotted Knapweed. ; On Nantucket, this species has been seen growing along the Madaket bike path heading west

Growth Form: Herb

Origin: Europe

Level of Invasiveness for Nantucket: Invasive

Level of Invasiveness for Massachusetts: Likely Invasive

Massachusetts Cultivation Restrictions: importation ban, propagation ban