In Irish folklore, white clover is the plant traditionally associated with good luck when it produces four leaves. The familiar four-leaf clover is an uncommon variation of the usual three-leaf form, and finding one has long been treated as fortunate.
Botanically, the plant is typically white clover, Trifolium repens. Most leaves have three leaflets, while a fourth leaflet results from a rare genetic variation. Estimates of frequency vary because they depend on habitat and searching methods, but four-leaf specimens are much less common than ordinary three-leaf leaves.
The four-leaf symbol is often confused with the shamrock. A shamrock traditionally has three leaflets and is associated with Ireland, especially through stories about Saint Patrick using the three-part leaf to explain the Christian Trinity. The four-leaf clover became a broader luck symbol in popular culture and is not limited to Ireland.