Shamrock is a traditional icon of the St. Patrick's Day. The name "shamrock" refers to a three-leafed plant, which Patrick used to explain the Trinity. He used the plant to describe how the Father, the Son, and the Holy Spirit all exist as separate elements of the same entity.

No one can agree, however, which plant was the original shamrock picked by Patrick. It could be any of the similar-appearing plants, each of whose leaves are devided into three leaflets. Plants called shamrock include the lesser trefoil (Trifolium dubium), the white clover (T. repens), the black medic (Medicago lupulina) or the wood sorrel (Oxalis acetosella). The lesser trefoil also goes by several other common names, such as suckling clover, hops clover, small hops clover, yellow shamrock and Kleiner Klee.