A shamrock is a small green plant with three leaves on each stem, closely associated with Ireland and Saint Patrick's Day. The word comes from the Irish seamróg, meaning “little clover.”

According to legend, Saint Patrick used the shamrock's three leaves to explain the Christian concept of the Trinity while teaching in Ireland during the 400s. Whether or not this actually happened, the shamrock became Ireland's most recognized symbol. Today, people around the world wear shamrocks on March 17 to celebrate Irish culture and heritage.

The shamrock is usually a young clover plant, though botanists debate exactly which species counts as a true shamrock. What matters most is the three-leaf pattern: finding a four-leaf clover is considered lucky precisely because it's not the usual three-leaf shamrock.

In Ireland, shamrocks grow wild in fields and meadows. Irish athletes wear shamrock emblems on their uniforms, and the plant appears on everything from Irish coins to airport signs.