SNIPPET: Like so many aspects of Irish history and culture, to find the origin of the shamrock as a significant feature of Irish life one must go back to pre-Christian times. Ancient Celts believed the shamrock, or white clover, possessed curative powers and could foretell the weather (its leaves were said to arch upward before a storm). The word shamrock derives from the Irish word Seamr g, or "summer plant." The shamrock's significance in modern times, however, comes from its association with St. Patrick. Legend has it (and all we have is legend since St. Patrick never mentioned the shamrock in his writings) that he used the shamrock to explain the mystery of the Trinity to pagan Celts by comparing the three leaves with the Father, Son, and Holy Spirit. Doubtless, some missionary, if not Patrick himself, used this unique teaching tool in the Christianization of Ireland in the fifth and sixth centuries. The practice of wearing shamrocks on St. Patrick's Day dates as far back as the sixteenth century, and perhaps earlier. The shamrocks became a symbol of Irish national identity in the nineteenth century when Nationalists adopted it as their symbol. Ironically, so too did Ulster Unionists for a time. -- Excerpt, "E. T. O'Donnell, "1001 Things Everyone Should Know About Irish American History," Broadway Books/NY (2002).