Centaurea cyanus

Centaurea cyanus, commonly known as cornflower or bachelor’s button,[note 1] is an annual flowering plant in the family Asteraceae native to Europe. In the past, it often grew as a weed in cornfields (in the broad sense of “corn”, referring to grains, such as wheat, barley, rye, or oats), hence its name. It is now endangered in its native habitat by agricultural intensification, particularly by over-use of herbicides. However, Centaurea cyanus is now also naturalised in many other parts of the world, including North America and parts of Australia through introduction as an ornamental plant in gardens and as a seed contaminant in crop seeds.

Centaurea cyanus is an annual plant growing to 40–90 cm tall, with grey-green branched stems. The leaves are lanceolate and 1–4 cm long. The flowers are most commonly an intense blue colour and arranged in flowerheads (capitula) of 1.5–3 cm diameter, with a ring of a few large, spreading ray florets surrounding a central cluster of disc florets. The blue pigment is protocyanin, which in roses is red.[3] Fruits are approx. 3.5 mm long with 2-3 mm long pappus bristles.[4] It flowers all summer.[5]

Centaurea cyanus is native to temperate Europe, but is widely naturalized outside its native range. It has been present in the British Isles as an archaeophyte (ancient introduction) since the Iron Age.[6] In the United Kingdom, it has declined from 264 sites to just 3 sites in the last 50 years.[7] In reaction to this, the conservation charity Plantlife named it as one of 101 species it would actively work to bring ‘back from the brink’.[8] In the County Clare (VC H9) in Ireland, Centaurea cyanus is recorded in arable fields as very rare and almost extinct,[9] while in the North-East of Ireland, it was abundant before the 1930s.[10]