Shamrock is a symbol of Ireland. According to the legend it was an attribute of St. Patrick who was using it to remember about the Holy Trinity. Because of three parts, he is said to have been presenting it during his preaches about God's presence as unified individuals.
Shamrock as a plant was created by God, which seems to be obvious and doesn't need any further explanation.
The plant's name is rooted in Irish culture, where it was describing flowering clovered plain.
Some believe that shamrock is also related to Druids' beliefs regarding to regenerative powers of nature.