SafePlants

Common Knapweed (Centaurea nigra)

Common Knapweed, also known as Black Knapweed or Hardheads, is a robust wildflower favored by pollinating insects. It's a familiar sight in grasslands and along roadsides across the British Isles and beyond.

Considerations for Pets

• Knapweed leaves can be spiny in some species.

Scientific Classification

• Scientific Name: Centaurea nigra
• Common Names: Lesser Knapweed, Common Knapweed, Black Knapweed, Hardheads
• Family: Asteraceae (Daisy family) / Compositae

Distribution and Habitat

• Native to Europe.
• Found across the UK, British Isles.
• Grows in various grasslands, including roadside verges, woodland rides, cliff tops, and lawns.
• Also found in dry, chalky soils.

Ecological Role

• Some Knapweed species are considered invasive weeds.
• Spotted Knapweed is considered an aggressive exotic species that spreads quickly.
• Russian Knapweed spreads slower than other species, but is still considered a noxious weed in some regions.
• Its presence can impact native grasslands.

Morphological Characteristics

• Thistle-like plant with reddish purple flowers.
• Flowers are typically purple, 20-40mm in size, and solitary or in branched groups.
• Grows as a perennial plant.
• Medium to tall hairy plant with erect stems, branched or unbranched.
• Leaves are deeply divided into elongated lobes, especially in the lower part of the plant.
• Stem leaves are lanceolate.

Interactions with Other Organisms

• A firm favorite of pollinating insects, especially towards the end of summer.
• Liked by bees and butterflies.

Resources and Further Information

• Find help & information on Centaurea nigra common knapweed from the RHS (Royal Horticultural Society).
• USDA's National Invasive Species Information Center provides a species profile for Spotted Knapweed.
• University of Wisconsin Weed-Factsheet provides information on Spotted Knapweed.
• Michigan State University Department of Entomology provides information on Spotted Knapweed management.