Oxalis, a large genus of low-growing herbs distantly related to geraniums. North American species are known as wood sorrels. The most common species are the yellow wood sorrel, the creeping wood sorrel, and the violet wood sorrel. Plants of the oxalis genus grow along roadsides and in fields throughout the Americas and in South Africa. Like clover, they have heart-shaped leaflets in clusters of three, but the leaflets, unlike those of clover, fold lengthwise at night, (Wood sorrel is one of the plants called the Irish shamrock.) The small, five-petaled flowers are white, yellow, pink, or red. They grow singly or in loose clusters of a few flowers. In the Andes, oxalis plants produce a widely eaten potatolike tuber called oca.

Yellow wood sorrel is Oxalis europaea; creeping, O. corniculata; violet, O. violacea. The plant yielding oca is O. tuberosa. These plants belong to the oxalis family, Oxalidaceae.