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COMMON KNAPWEED Centaurea nigra (Asteraceae) Height less than 1m. Downy or hairy perennial that branches towards the top of the plant. The stems are stiff and grooved and are often swollen beneath the base of the flowers. Grows in a wide range of grassy places. FLOWERS are borne in heads, 2-4cm across, with reddish purple florets and a swollen, hard base covered in brown bracts; heads are usually solitary (Jun-Sep). FRUITS do not have pappus hairs. LEAVES are narrow, those near the base of the plant are slightly lobed.