Common wood sorrel

Oxalis acetosella

''Oxalis acetosella'' is a rhizomatous 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. The common name wood sorrel is often used for other plants in the genus ''Oxalis''. In much of its range it is the only member of its genus and hence simply known as "the" wood sorrel. While common wood sorrel may be used to differentiate it from most other species of ''Oxalis'', in North America, ''Oxalis montana'' is also called common wood sorrel. It is also known as ''Alleluia'' because it blossoms between Easter and Pentecost, when the Psalms which end with Hallelujah were sung.

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 10cm 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.

As with other species of wood sorrel, the leaves are sometimes eaten. An oxalate called "sal acetosella" was formerly extracted from the plant, through boiling.

The common wood sorrel is sometimes referred to as a shamrock and given as a gift on St. Patrick's Day. This is due to its trifoliate clover-like leaf, and to early references to shamrock being eaten. Despite this, it is generally accepted that the plant described as shamrock is a species of clover, usually white clover .