Common Knapweed

A valuable source of nectar for insects in late summer, Common Knapweed is found on the grasslands and scrub of The Lizard from July to September.
Photo: Steve Townsend

Scientific name: Centaurea nigra

Other common names: Black Knapweed, Hardheads, Paintbrush, Loggerheads, Sweeps, Lesser Knapweed

Cornish name: ‘Pedripromter’ is the word for ‘Knapweed’, literally translating as ‘Priest’s head’.

Conservation status: No designations

Common Knapweed is a plant of grasslands, roadsides and waste ground across the British Isles. Reaching up to a metre in height, this perennial member of the Daisy family (Asteraceae) has linear- to lanceolate-shaped leaves and purple flowerheads, appearing from July to September at the end of each branching stem. Both stems and leaves are grooved and hairy. The involucral bracts (found below the flowerhead) of Common Knapweed are brown-black, hence its alternative common name of Black Knapweed and the species name of nigra, derived from the Latin word for the colour black.

A much rarer form of this plant occurs in local populations in which the florets of the flowerheads are rayed rather than the more usual clustered and upright form. This can lead to confusion with Greater Knapweed (C. scabiosa), in which the flowerheads are always rayed, but the two can be distinguished by the green involucral bracts of the latter.

The plant has significant value as a nectar source for several species of butterflies, as well as for honey and bumble bees, hoverflies and other invertebrates. Birds are also attracted to Common Knapweed: young Goldfinches eat the seeds, and other small birds feast on the invertebrates nectaring on the flowerheads.







Did you know…?

…Where it has been introduced to continents outside its natural European range, it has in some cases become invasive.

…It was once used in a traditional game by young women to divine their ‘true love’ (Mabey, 1997).

More information and references:

Mabey, R., 1997. Flora Britannica. Chatto & Windus, London.

Rose, F. and O’Reilly, C., 2006. The Wild Flower Key, 2nd edition. Frederick Warne, London.

Stace, C., 2010. New Flora of the British Isles, 3rd edition. Cambridge University Press, Cambridge.

Published: September 2013
Author: Amanda Scott
Photos: Steve Townsend