Allium cepa, L.

20. A. cepa L. , Sp. Pl. 301 (1753) View Cited Treatment

(incl. A. ascalonicum auct., non L.).

Bulbs varying in size and shape from cultivar to cultivar, often depressed-globose and up to 10 cm in diameter; outer tunics membranous. Stem up to 100 cm and up to 30 mm in diameter, tapering from inflated lower part. Leaves up to 10, up to 40 cm and up to 20 mm in diameter, usually almost semicircular in section and slightly flattened on upper side, basal in first year, in second year their bases sheathing the lower | of the stem. Spathe often 3-valved, persistent, shorter than the umbel. Umbel 4-9 cm in diameter, subglobose or hemispherical, dense, many-flowered; pedicels up to 40 mm, almost equal. Perianth stellate; segments 3-4-5 x 2-2-5 mm, white, with green stripe, slightly unequal, the outer ovate, the inner oblong, obtuse or acute. Stamens exserted; filaments 4-5 mm, the outer subulate, the inner with an expanded base up to 2 mm wide and shortly toothed on each side. Ovary whitish. Capsule c. 5 mm. 2n = 16. Cultivated on a field scale throughout most of Europe for its edible bulbs (onions).

The common onion exists in numerous cultivars resulting from some 3,000 years of cultivation and is usually grown as a biennial, but there are perennial variants with narrow leaves or with large bulbils and usually few flowers in the umbel (cf. H. A. Jones & L. K. Mann, Onions and their Allies 32- 36 (1963)). It is unknown in a wild state, though probably derived from A. oschaninii B. Fedtsch. ( A. cepa var. sylvestre Regel ) of C. Asia. A. cornutum G. C. Clementi ex Vis. , Fl. Daim. 1: 139 (1842), from S.W. Jugoslavia (near Budva), may be a bulbilliferous form derived from former cultivation. The name A. ascalonicum L. was based on a Palestinian species later named A. hierochuntinum Boiss. , but has long been applied to variants of A. cepa called shallots (cf. W. T. Stearn, Bull. Brit. Mus. (Bot.) 2: 181 (I960)).