Common Wood-sorrel is a plant from the genus Oxalis, common in most of Europe and parts of Asia. The binomial name is Oxalis acetosella, because of its sour taste. In much of its range it is the only member of its genus and hence simply known as "the" wood-sorrel.

The plant has heart-shaped leaves, folded through the middle, that occur in groups of three atop a reddish brown stalk. It flowers for a few months during the spring, with small white flowers with pink streaks. Red or violet flowers also occur rarely.During the night or when it rains both flowers and leaves contract.

Wood sorrel has been eaten by humans for millennia. In Dr. James Duke's "Handbook of Edible Weeds," he notes that the Kiowa Indian tribe chewed wood sorrel to alleviate thirst on long trips, that the Potawatomi Indians cooked it with sugar to make a dessert, the Algonquin Indians considered it an aphrodisiac, the Cherokee tribe ate wood sorrel to alleviate mouth sores and a sore throat, and the Iroquois ate wood sorrel to help with cramps, fever and nausea.[1] Wood sorrel, like spinach and broccoli, contains oxalic acid which is considered slightly toxic because it interferes with food digestion and the absorption of some trace minerals. However, the U.S. National Institutes of Health have determined that the negative effects of oxalic acid are generally of little or no nutritional consequence in persons who eat a variety of foods.[2] An oxalate called "sal acetosella" was formerly extracted from the plant, through boiling.

The "Common wood sorrel" of North America is Oxalis montana, found from New England and Nova Scotia to Wisconsin and Manitoba and more unambiguously known as Mountain Wood-sorrel. It is similar to the species described above, but the petals are noticeably notched. It is called sours in the Northeast US.