The Knapweed,Centaurea nigra

This plant with its thistle like flowers adorns the countryside in late summer, where it can be found in a variety of locations which includes meadows,rough grasslands and by farm tracks. They belong to the Order Asterales and within that Order they are placed in the family Asteraceae {formerly the Compositae} and grouped in the Genus Centaurea. This genus consists of between 3 and 600 species world wide. The common knapweed also known as the black knapweed is often referred to as hard heads.

Components of knapweed. illustration courtesy of Joann Garg Sturm Creative Commons Share Alike 

New seasons foliage

photograph by Dal

Description of the common Knapweed

The common knapweed is a robust hairy perennial that attains the height of 3 feet {90 cm}. The root is a rhizome, from which arise stems that are grooved and branched towards the summit. The lower basal leaves can be as much as 25-30 cm long, stalked and may be shallowy lobed or almost entire rarely toothed. The stem leaves are smaller stalkless and end in a point. They are arranged alternately.

The foliage expanding

photograph -Dal


The flowers as previously stated are thistle like in appearance consisting of tubular florets 2-3 cm wide, all of equal length, below which are many overlapping dark or black bracts. When in bud these bracts which protect the florets are really hard, hence the country title of "hardheads". The shape of the closed flower head also give the flower its common name of knapweed. they have the shape of the small knobs that adorned drawers and cuboards that were popular in days gone by. Knap is the old English word for knob.

The flowers are produced from June until September. The florets sometimes have a white or yellowish hues. As a rule the florets are purplish red. The flower stems when cut just before the flowers open last well in water and make an attractive addition to an arrangement of flowers.

The flowers attract many insects in the localities they adorn, such as the Gatekeeper, Peacock and Meadow brown butterflies, Honey bee, Bumble bee and Hoverfly along with the Goldfinch that feeds on the seed with relish. 

Bumblee bee on knapweed


The knapweed is an unpopular weed in some countries

In many countries it occurs as an introduced  alien that is not looked upon with any favour. Take as an example King County Washington DC  in the USA. the knapweed is classed as a class B noxious weed. Control is required in King County. In the County knapweed cross pollinate The black knapweed X brown knapweed which produce plants that" are aggressive and invasive in pastures and meadows" according to the State Noxious Weed Control Board.

Historical uses in medicinal preparations.

There follows below an extract from a Family Herbal published in 1820-----

" The young plant is used fresh; a decoction of it id good against bleeding of the piles, against looseness with bloody stools and all other bleedings. A slight infusion is recommended against sore throats to be used by way of a gargle. There are so many of these  gentle astringent plants, common in our fields as yarrow and the like, that less respect is to be paid to one of less power in the same way. Knapweed may be properly added to decoctions of the others but it would not be so well to trust to its effects singly."


 Although still used until the 1930s or so it is not recommended for home made preparations. 

Any one thinking of using or making herbal medicine for the first time is advised to click on the content banner WILD HERB ADVISE . 

Knapweed summer blooms clearly showing the hard dark bracts below the flower


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