Centaurea cyanus (Cornflower)

Plant Info
Also known as: Bachelor's Buttons, Bluebottle, Garden Knapweed
Genus:Centaurea
Family:Asteraceae (Aster)
Life cycle:annual
Origin:Europe
Habitat:part shade, sun; disturbed soil; roadsides, fields, shores, gardens
Bloom season:June - September
Plant height:8 to 40 inches
Wetland Indicator Status:GP: FACU MW: FACU NCNE: UPL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 7+petals

[photo of flower] Showy flower heads up to about 1¼ inches across, single at the tips of branching stems. Each head has 25 to 35 florets, consisting of a series of large ray flowers around the outer edge and shorter disk flowers in the center. Ray flowers are sterile, widely spreading, funnel-shaped with 5 lobes shorter than the tube, and the color ranging from blue to purple to pink to white. Disk flowers are fertile, erect to ascending, purple to white with a column of dark blue-violet tipped stamens and a divided style.

[photo of phyllaries] The bracts (phyllaries) surrounding the base of the flower are in several layers, appressed, egg-shaped, light green with finely toothed, whitish to brown edging around the tip end, and the surface sparsely covered in matted white hairs. The entire set of phyllaries (involucre) is ½ to 2/3 inch long and longer than wide.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves and stem] Leaves are alternate, 1 to 4 inches long, lance-linear, pointed at the tip, stalkless, toothless or occasionally the lower leaves with a few narrow lobes. Surfaces are sparsely to moderately covered in long, matted hairs. Stems are usually single from the base, branched, sparsely to moderately covered in woolly hairs, and initially erect but tend to flop over without support of surrounding vegetation.

Fruit: Fruit type: seed_with_plume

[photo of fruit] Seeds are oblong-elliptic, 4 to 5 mm long, finely hairy, straw-colored at maturity with a tuft of short, stiff, light brown bristles at the tip.

Notes:

Cornflower is an annual, native to the Mediterranean but widely naturalized far beyond its native range, and is commonly included in “wildflower” seed mixes. While not especially hardy in Minnesota, it occasionally escapes cultivation and has been noted as an agricultural pest in parts of the southeastern US. It's not likely to be confused with any other species except other garden variety Centaura species, but the woolly hairy leaves and stems should be stand-out traits. Flowers are typically blue but cultivated varieties come in a range of colors from shocking pink to purple to white.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken in the garden. C. cyanus at the edge of a field by Stefan.lefnaer, via Wikimedia Commons, used under CC BY-SA 4.0

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