The green shamrock (trefoil or seamairog) is the national symbol of Ireland however they may come in white, red or yellow. Druids, ancestors of the modern Irish people believed in the holiness of the shamrock because of the sacred symbol formed by its three leaves ( hope, love, and faith).

The Legend Behind The 'Four-leaf clover'
The Druids belived a four-leaf clover could help in spotting witches or other demons. Some modern-day spiritualists claim that a four-leaf clover releases energy and helps one's judgment. Others feel that finding a four-leaf clover brings good luck and fortune on days other than St. Patricks Day.