oxalis or wood sorrel, any species of the plant genus Oxalis. Most of the cultivated kinds are tropical herbs used as window plants. The leaves are usually cloverlike and respond to darkness with "sleep" movements by folding back their leaflets. Several species grow wild in North America, including the white wood sorrel (O. acetosella), widely distributed in the north temperate zone and one of the plants identified as the shamrock. This and, to a lesser extent, other species have long been used for salads and greens because of their pleasantly acid taste; these species contain oxalic acid. O. tuberosa has a starchy tuber that has been valued in the high Andes for centuries. Although species of Oxalis are called sorrels, the genus is unrelated to the true sorrel, or dock (genus Rumex), of the buckwheat family. Oxalis is classified in the division Magnoliophyta, class Magnoliopsida, order Geramales, family Oxalidaceae.