3. Allium cepa L. (onion)

Pl. 100 a; Map 398

Bulbs 2–6 cm long, narrowly ovoid to depressed-globose, the outer coat smooth and papery. Aerial stems 60–150 cm long, inflated in the basal half, erect at flowering. Leaves in the lower 1/3–1/2 of the aerial stems, 10–50 cm long, 5–15 mm in diameter, tubular, circular to depressed-circular in cross-section and hollow, linear, not tapering to a petiole, usually glaucous, the sheaths green to white or yellow. Umbels with 0–100 or more normal flowers, some or all of the flowers sometimes replaced by sessile bulblets. Flower stalks much longer than the flowers. Perianth bell-shaped to nearly tubular, the sepals and petals 4–7 mm long, narrowly ovate, the tips pointed, purplish pink to white or greenish white. Fruits 3–5 mm long, globose to depressed-globose, 3-lobed, the angles or lobes with a thickened ridge. 2n=16, 32, 64. May–July.

Introduced, uncommon and widely scattered in the state (native of southwestern Asia, commonly cultivated nearly worldwide; widely but sporadically escaped from cultivation in the U.S.). Railroads and other highly disturbed areas.

The cultivated onion presumably has not become fully naturalized in Missouri, but it is included in the flora based upon its persistence in waste ground of areas removed from those where it is cultivated. The various onions with well-developed bulbs and strictly floriferous inflorescences that have numerous culinary uses are sometimes known as var. cepa. Plants with slender bulbs and most or all of the flowers replaced by bulblets have been called var. viviparum Metz, or top onion, and are a phase of the species used commercially for propagating purposes.