Aside from the violet, which was embraced by Athens, the shamrock is the oldest national flower… well, kind of. It’s not a flower but anyway, how was that decided? The story is told that Saint Patrick used it as an example of how the Trinity (Father, Son and Holy Ghost) could also be one (God). The legend is that he was trying to teach his Christian beliefs to pagans, so he picked a spray of shamrock that was blooming on the ground and had them observe that three leaves are united on one stalk, representing his belief that the Father, Son and Holy Spirit make up the one God.
Suellen Ocean is the author of the historic novel The Celtic Prince Available here: http://www.amazon.com/Celtic-Prince-Before-After/dp/1484086392