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.

[3] Centaurea cyanus is an annual plant growing to 20–100 centimetres (8–39 in) tall, with grey-green branched stems.

[12] 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'.

The occurrence of Centaurea cyanus strongly decreased during the last decades due to improved seed cleaning, more intensive nitrogen fertilization and herbicide use.

[18] Due to its strong roots, Centaurea cyanus is difficult to control mechanically in spring.

Field experiments showed that planting Centaurea cyanus in cabbage fields at a density of 1 plant / m2 can result in a significant increase in parasitation of Mamestra brassicae larvae, predation of Mamestra brassicae eggs (e.g. by carabid beetles or spiders) and ultimately cabbage yield.

[22] Several cultivars of Centaurea cyanus with varying pastel colours, including pink and purple, have been selected for ornamental purposes.

As for all ornamental plants, important goals of Centaurea cyanus breeding include the induction of phenotypic variation (e.g. in flower coloration, size and shape, foliage characteristics or plant height), higher flower yield, resistance to pests and diseases as well as tolerance to abiotic stress (e.g., extreme temperatures, drought or salinity).

Mulching is recommended to prevent drying out of the soil and exposure of the root system to the sun.

Cornflowers are often used for ornamental purposes and by cutting them, up to their third leaves, they will produce more blooms and grow a bigger stem.

Petals can also be added to salads, drinks, and desserts for garnishing purposes in raw or dried form.

[30] Centaurea cyanus contains a wide range of pharmacologically active compounds, such as flavonoids, anthocyanins and aromatic acids.

[31] Especially the flower head finds application in herbal medicine, but leaves and seeds are also used for pharmacological purposes, albeit to a lesser extent.

[33] Furthermore, extracts of the flower head and vegetative parts of the plant were shown to have gastroprotective effects due to their content of quercetin, apigenin and caffeic acid derivates.

[34] The blue color of Centaurea cyanus is due to protocyanin, an anthocyanin pigment that is also found in roses.

(bacterium) would significantly enhance the biomass production and lead uptake of Centaurea cyanus.

[38] This is partly due to the story that when Queen Louise of Prussia was fleeing Berlin and pursued by Napoleon's forces, she hid her children in a field of cornflowers and kept them quiet by weaving wreaths for them from the flowers.

[48] Because of its ties to royalty, authors such as Theodor Fontane have used it symbolically, often sarcastically, to comment on the social and political climate of the time.

[citation needed] Due to its traditional association with Germany, the cornflower has been made the official symbol of the annual German-American Steuben Parade.