When you put on your green shamrocks to come out to Patty in the Parc, now you'll know why you're putting them on!

The Shamrock has been considered the unofficial national flower of Ireland for centuries.

Irish legend has it that St. Patrick used the shamrock as a teaching tool to explain the Holy Trinity to non-believers as he converted the Irish to Catholicism all the way back in the fourth century.

To further it along, those that were living in poverty in the 17th century, but still wanted to look nice at church would where the shamrock to look nice for the saint's feast day.

And, of course, Hallmark had something to do with it. The tradition further spread when the cardmakers started using the shamrock on post cards from around 1910-1915.