Red star thistle

Centaurea calcitrapa, the red star thistle or purple star-thistle, is an erect, much-branched biennial or short-lived perennial herb in the family Asteraceae, native to Europe, North Africa and western Asia and widely naturalised as a weed of disturbed ground, roadsides and overgrazed pasture across the temperate world. It typically reaches 20 to 70 centimetres in height, with a rosette of deeply pinnatifid, hairy basal leaves in the first year and a wiry, divaricately branched, leafy flowering stem in the second. The pink to bright rose-purple flower heads are about 1.5 centimetres across and are surrounded by an involucre of bracts each terminating in a long, rigid, straw-coloured spreading spine 1.5 to 2.5 centimetres long, giving the heads their distinctive armoured, star-shaped appearance and the plant its English and Latin names, calcitrapa referring to the medieval caltrop. The fruit is a small, smooth, pale achene without a pappus.