Centaurea nigra is a species of flowering plant in the daisy family known by the common names lesser knapweed, common knapweed and black knapweed. A local vernacular name is hardheads.
It is a perennial herb growing up to about a metre in height.
The leaves are up to 25 centimetres long, usually deeply lobed, and hairy. The lower leaves are stalked, whilst the upper ones are stalkless.
The inflorescence contains a few flower heads, each a hemisphere of black or brown bristly phyllaries. The head bears many small bright purple flowers. The fruit is a tan, hairy achene 2 or 3 millimetres long, sometimes with a tiny, dark pappus. It flowers from July until September. The flowers sometimes are yellow or white
In Europe, the plant is an important source of food for the European goldfinch, honey bee, lime-speck pug moth, and the following butterflies: large skipper, meadow brown, small heath, painted lady, peacock, red admiral, small copper and small skipper.
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