They are a variation on the common three-leaf white clover (Trifolium repens). Researchers from the University of Georgia believe a combination of genes and environment makes them sprout an extra leaf. Exactly how rare they are is debatable. According to experts, the probability of finding one is 1 in 5,000 or 1 in 10,000.

These are actually Pepperwort or Water Clover (Marsilea Quadrifolia and Marsilea Polycarpa) or Oxalis (Oxalis deppei or Oxalis tetraphylla) plants that produce all four leaves.

The flowers are small and bright yellow. The leaves are trifoliate and heart- shaped like shamrocks. The seed pods are cylindrical. The leaves curl up at night and open in the morning to photosynthesize.