"shamrock"

shamrock three-lobed, low-growing plant, the 'little clover', national symbol of Ireland and the Irish, along with the Irish harp. Four species of clover are claimed as the true shamrock, the most popular is the lesser clover (trifolium dubium). The earliest literary reference to wearing shamrock on St Patrick's Day is from 1681. According to a late (1727) tradition, St Patrick used its three leaves to explain the doctrine of the Trinity to the pagan Irish.