Common Knapweed
Centaurea nigra is a species of flowering plant in the family Asteraceae known by the common names lesser knapweed, common knapweed and black knapweed. A local vernacular name is hardheads
The tightly packed, thistle-like purple flower heads of common knapweed bloom on all kinds of grasslands.
This plant attracts clouds of butterflies
It is native to Europe but it is known on other continents as an introduced species and often a noxious weed
Although the plant is often unwanted by landowners because it is considered a weed by many, it provides a great deal of nectar for pollinators
It is a herbaceous perennial growing up to about a metre in height
The leaves are up to 25 centimetres (9.8 in) 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. Each 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
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