SAINT PATRICK became associated with the shamrock through the tradition that he used the three leaf plant to explain the Holy Trinity to converts. Although this traditional belief existed for many years, the first written reference to the tale dates from 1727 in an article on native Irish plants by the botanist Caleb Threlkeld. He refers to the "current tradition that by this three-leaved grass, he (saint Patrick) emblematicaly set forth to them (the Irish) the mystery of the Holy Trinity".
For millions of people today, the shamrock is the emblem of Ireland. The shamrock seems to have acquired its emblematic symbolism at the same time as it became associated with Saint Patrick, in the late seventeenth and early eighteenth centuries.

The association between Saint Patrick and the shamrock grew during years of widespread suppression of Irish Catholics and the confiscation of their lands. The first time that the shamrock was put into the hand of Saint Patrick who offers it to assembled people, was on a coin issued by the Confederate Catholics of Kilkenny in 1645. The Confederates were Royalists who wanted to barter their loyalty for freedom to practise Catholicism and ensure the return of their confiscated land.