22.
Allium cepa
Linnaeus, Sp. Pl. 1: 301. 1753.
Cultivated onion
Bulbs 1—3, not rhizomatous, mostly depressed-globose, varying in size from cultivar to cultivar, 5—8 × 3—10 cm; outer coats enclosing 1 or more bulbs, yellowish brown, red, or white, membranous, without reticulation; inner coats white to pink, cells obscure to quadrate. Leaves persistent, 4—10, sheathing proximal 1/6—1/4 scape; blade fistulose, usually ± semicircular in cross section, 10—50 cm × 4—20 mm. Scape persistent, solitary, erect, fistulose, inflated below middle, 30—100 cm × 3—20 mm. Umbel persistent, erect, compact, to 500-flowered, globose, bulbils occasionally found; spathe bracts caducous, 2—3, 3—4-veined, ovate, ± equal, apex acute to acuminate. Flowers stellate to campanulate to urceolate, 3—7 mm; tepals erect to ± spreading, white to pink with greenish midveins, withering in fruit, margins entire, apex obtuse or acute, outer ovate, inner oblong; stamens exserted; anthers white; pollen white; ovary crestless; style linear, ± equaling stamens; stigma capitate, unlobed; pedicel 10—50 mm. Seed coat not known.
Flowering Jun--Aug. Disturbed sites adjacent to areas where cultivated; 0--500 m; Ark., Calif., Kans., La., Mont., Oreg., Tex., Wash.; cultivated in Europe, Asia.
The onion of commerce, Allium cepa is widely cultivated as a biennial in North America, Europe, and Asia. It is unknown in the wild and is probably derived from A. oschanini of central Asia. The cultivated form is often polyploid (2n = 16, 32, 54) and possibly of hybrid origin. It exists in numerous cultivars, a few of which form large bulbils in the umbel.
