The shamrock is a three-leafed old white clover. It is known as a symbol of Ireland. The name shamrock is derived from Irish seamróg, which is the diminutive version of the Irish word for clover (seamair).
It is sometimes of the variety Trifolium repens (white clover, Irish: seamair bhán) but today usually Trifolium dubium (lesser clover, Irish: seamair bhuí). However, other three-leafed plants — such as Medicago lupulina, Trifolium pratense, and Oxalis — are sometimes designated as shamrocks. The shamrock was traditionally used for its medical properties and was a popular motif in Victorian times.
Traditionally, shamrock is said to have been used by Saint Patrick to illustrate the Christian doctrine of the Trinity when christianising Ireland in the 6th century. However, this is described by the Oxford English Dictionary a "a late tradition", first recorded in 1726, and is probably false. None the less, since the 18th century, shamrock has been used as a symbol of Ireland in a similar way to how a rose is used for England, thistle for Scotland and leek for Wales.
Shamrock commonly appears as part of the emblem of sporting and official organisations representing both the whole of Ireland (such as the Irish Rugby Football Union or Tourism Ireland) as well as organisations specific to the Republic of Ireland (such as IDA Ireland) and Northern Ireland (such as Police Service of Northern Ireland). Shamrock is also used in emblems of UK organisations with an association with Ireland, such as the Irish Guards.