Black Knapweed

Centaurea nigra

Family: Asteraceae.

Form: Herb

Origin: Native of Europe.

Flowers/Seedhead: Many small flowers (florets) in solitary heads at ends of branches. Flowers spring to autumn.

Description: Perennial erect herb to 0.9 (rarely to 1.2) m high. Stems ribbed, cobwebby, sometimes hairless with age. Basal leaves entire to lobed, 6–30 cm long, 0.5–3.5 cm wide, narrowed at base, withering in mature plants; lower stem leaves entire to toothed 1–8 cm long, 0.2–1 cm wide; upper leaves smaller, entire to sparsely toothed, oblong to lanceolate. Seeds flattened, 3–4 mm long, sparsely short hairy, pale brown, topped by a few bristles to 1 mm long or without bristles.

Distinguishing features: Distinguished by presence of rhizomes; erect habit; leaves not spiny; flowerheads mostly 12–18 mm wide; middle bracts with a narrow waist between base and fringed upper section, fringe hairy, dark brown top blackish; all florets tubular, pink to purple (rarely white), arising from a hairy receptacle, outer petal-like florets with forked tips.

Dispersal: Spread by seed, rhizomes and root pieces.