Oxalis acetosella, the wood sorrel or common wood sorrel, is a rhizomatous flowering plant in the family Oxalidaceae, common in most of Europe and parts of Asia. The specific epithet acetosella refers to its sour taste.
The plant has trifoliate compound leaves, the leaflets heart-shaped and folded through the middle, that occur in groups of three on petioles up to 10 centimetres long. It flowers from spring to midsummer with small white chasmogamous flowers with pink streaks. Red or violet flowers also occur rarely. During the night or when it rains the flowers close and the leaves fold.