A thistle-like purple tuft with no spines at all, sitting on a hard black knob of fringed bracts
Common knapweed — Centaurea nigra.
Nature · Wildflowers & flowers
Common knapweed
Flowers June to September
Centaurea nigra — Asteraceae
Common knapweed, or black knapweed, is the thistle-like purple composite of hay meadows, verges and chalk downland, but with no prickles anywhere on it. The hard, almost black, fringed involucre under each head gives it both its English name — knap, a knob — and its epithet nigra. It is one of the best nectar plants in British grassland, and a favourite perch for marbled whites and common blues.
How to spot them
- ▸A hard, rounded, knob-like bud below the flower, with dark brown or black fringed bracts
- ▸Bright pink-purple florets in a shaving-brush tuft; no spines anywhere on the plant
- ▸Tough, grooved, branching stems to about 1 m with narrow, slightly lobed leaves
- ▸Unimproved grassland, hay meadows, verges, cliff tops and waste ground, June to September
- ▸Greater knapweed has deeply pinnate leaves and enlarged spreading outer florets; this one usually does not
How to know it
Its English name comes from an Old English word for a knob or lump, and its epithet means black
Common knapweed — knap, hence also hardheads.
Called hardheads; one of the top nectar plants of British grassland for marbled whites and common blues
Common knapweed.
In the same genus as the cornflower, named for the centaur who healed his wound with it
Common knapweed — Centaurea nigra; the genus is named for Chiron.
The larger relative has deeply pinnate leaves and a ring of enlarged, spreading outer florets
Greater knapweed, Centaurea scabiosa, versus the common knapweed.
Girls were said to put the head under an apron and see whether the unopened florets came out, to learn if love was coming
Common knapweed — a traditional divination.
Its seeds are a favourite of goldfinches, and it is a hay-meadow indicator of unimproved grassland
Common knapweed.
Quick-fire facts
- •Family Asteraceae; Centaurea nigra, sometimes treated with the related Centaurea debeauxii
- •nigra, black, refers to the dark fringed bracts of the involucre, not to the flowers
- •The English name comes from 'knap', a knob or protuberance, as does the alternative name hardheads
- •It looks like a thistle but has no spines, which is the quickest way to tell them apart
- •The Wildlife Trusts describe it as growing to 1 m, flowering June to September, and being notably attractive to butterflies
- •Greater knapweed, Centaurea scabiosa, is the larger chalk-grassland species with pinnately divided leaves and enlarged outer ray florets
- •The genus Centaurea takes its name from Chiron the centaur
- •A valued nectar source for marbled white, common blue, meadow brown and six-spot burnet; seeds eaten by goldfinches
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Sources
- The Wildlife Trusts — Common knapweed