Spotted Knapweed
Centaurea stoebe var. micranthosAsteraceae
Whole Plant
Flower
Habitat
Whole PlantFlowerHabitat
Photos (c) Cheryl Comeau Beaton unless otherwise noted

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




Credits: The Electronic Field Guide to the Invasive Plants of Nantucket (c) 2005-2006 Maria Mitchell Association, EFG Project, UMass Boston