1. Centaurea cyanus Linnaeus, Sp. Pl. 2: 911. 1753.
Bachelor’s-button, garden cornflower, cornflower, bluebottle, bluebonnets, blaver, blue-poppy, thimbles, brushes, corn pinks. witch’s bells, hurtsickle, bleuet, barbeau, casse lunette
Leucacantha cyanus (Linnaeus) Nieuwland & Lunell
Annuals, 20–100 cm. Stems usually 1, erect, ± openly branched distally, loosely tomentose. Leaves ± loosely gray-tomentose; basal leaf blades linear-lanceolate, 3–10 cm, margins entire or with remote linear lobes, apices acute; cauline linear, usually not much smaller except among heads, usually entire. Heads radiant, in open, rounded or ± flat-topped cymiform arrays, pedunculate. Involucres campanulate, 12–16 mm. Phyllaries: bodies green, ovate (outer) to oblong (inner), tomentose or becoming glabrous, margins and erect appendages white to dark brown or black, scarious, fringed with slender teeth ± 1 mm. Florets 25–35; corollas blue (white to purple), those of sterile florets raylike, enlarged, 20–25 mm, those of fertile florets 10–15 mm. Cypselae stramineous or pale blue, 4–5 mm, finely hairy; pappi of many unequal stiff bristles, 2–4 mm. 2n = 24 (Russia).
Flowering spring–summer (May–Sep). Grasslands, woodlands, forests, roadsides, other disturbed sites; 50–2400 m; introduced; Greenland; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.). N.S., Ont., P.E.I., Que., Yukon; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; s Europe.
Centaurea cyanus is a commonly cultivated garden ornamental. Its cypselae are often included in wildflower seed mixes and it naturalizes readily in many areas.