OXALIS, in botany, a large genus of small herbaceous plants, comprising, with a few small allied genera, the family Oxalidaceae. The name is derived from Gr. 6Evs, acid, the plants being highly acid to the taste. It contains about 30o species, chiefly South African and tropical and South American. It is represented in Great Britain and eastern North America by the wood-sorrel (0. Acetosella), a small, stemless plant with radical, trefoil-like leaves growing from a creeping, scaly rootstock, and the flowers borne singly on an axillary stalk; the flowers are regular with five sepals, five obovate, white, purple-veined, free petals, ten stamens and a central five-lobed, five-celled ovary with five free styles. The fruit is a capsule, splitting by valves; the seeds have a fleshy coat, which curls back elastically, ejecting the true seed. The leaves, as in the other species of the genus, show a "sleep-move ment," becoming pendulous at night.
Besides the wood-sorrel, some 20 other species occur in North America, among which are the yellow wood-sorrel (0. stricta),
of the eastern United States and Canada, with yellow flowers; the violet wood-sorrel (0. violacea), of the eastern United States, with rose-purple flowers; the redwood wood-sorrel (0. oregana), of the coast redwood belt from California to Oregon with pink to white flowers and 0. cernua, known as Bermuda buttercups, with showy yellow flowers, native to South Africa and naturalized in Florida and the Bermudas.
Oxalis crenata, the oca of South America, is a tuberous-rooted half-hardy perennial, native of Peru. Its tubers are comparatively small, and somewhat acid ; but if they be exposed in the sun from six to ten days they become sweet and floury.
Oxalis Deppci, a bulbous perennial of Mexico, has scaly bulbs, from which are produced fleshy, tapering, white, semi-transparent, edible roots, about 4 in. in length and 3 to 4 in. in diameter.
Various species are in cultivation as basket plants for window gardens, border plants and hot house ornamentals.