This is a very well-known perennial which grows in abundance in a wide variety of habitats owing to its very efficient seed dispersal method, being wind spread on tiny parachutes. Resembling a thistle without all the prickles, Common Knapweed is essentially a plant with reddish-purple 2-4cm flowerheads of florets and a swollen base of blackish bracts – a bit like an old fashioned shaving brush. Each flower is solitary or in branched clusters. The grey-green lanceolate leaves grow alternately up the stiff stems and are lobed slightly at the base of the plant. Common Knapweed is on flower from June to October. It is also known as Black Knapweed, Hardheads, Blackheads and Mullach dubh, and is a native plant belonging to the family Asteraceae.
I first identified this plant in Shanganagh, Co Dublin in 1976 and photographed it in Gibletstown, Co Wexford in 2005.
If you are satisfied you have correctly identified this plant, please submit your sighting to the National Biodiversity Data Centre