Cornflower is a species of knapweed with the scientific name Centaurea cyanus. Most of species in the genus Centaurea originated in Europe, but a few are native to the Americas including the cornflowers. The cornflower has many synonyms such as garden cornflower, bachelor's button, bluebottle, Hurtsickle, etc.
The cornflowers grow up to 1-3 feet high. Those are wiry, slender, furrowed, and branched. The feature of leaves is very thin and long. and leaves are arranged alternately on the stem. The species of cornflower focus on height are can be divided two. Tall and Dwarf, Tall and double-flowered forms are particularly valuable in a cutting garden. Dwarf forms of centaurea, especially the Florence series, with their 10 to 20 inch height and naturally compact, bushy growth habits, are good choices for edging a garden or filling out a container. 
Centaureas produce single and double, fringed blooms on plants that range in height from 10 inches to 2-1/2 feet, depending on the species or cultivar, basket flower can reach 4 feet in height. The shape of the flower petals resembles that of thistles, but the plants leaves do not have the spines of the latter. The leaves are often an attractive gray-green. Mountain bluet grows about two feet tall with an equal spread. The flowers are usually lavender blue, but you may also find plants with rose, pale yellow, or white blooms. 
The cornflower is an annual plant of arable fields that means favours sandy acidic lands. Plant centaureas(cornflower) in full or partial sun in any average, slightly alkaline soil. They do not too particularly need fertility. In hot zones, such as 8 to 10 and desert areas, bachelor-buttons will grow better with some shade from the midday sun.
The flowers are the part used in modern herbal medicine and are used as a tonic. Flowers have properties such as stimulant and emmenagogue. A distilled water from Cornflower petals can be used as a remedy for weak eyes. The famous French eyewash, 'Eau de Casselunettes,' used to be made from cornflower petals. Culpepper tells us that the ground leaves of the Bluebottle give good-working medicine for bruise or broken a vein inwardly. The condensed juice of the petals gives us a good blue ink; if condensed juice get mixed with alum-water, it can be used in water-colour drawing. It dyes linen a beautiful blue, but the colour is not permanent. Also, the dried petals can be used as a perfume. 
- taxonomy USDA
- Centaurea Cyanus, the Cornflower A Modern Herbal by Mrs M. Grieve F.R.H.S. 1931.
- WeedUs Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
- Florida Gardener National Garden Bureau
- Statues & Ecology