Four-leaf clover
2) A four-leaf clover is the result of a genetic abnormality or mutation in the white clover (Trifolium repens). Normally clover has three leaves. The fourth is caused by a growth defect, often influenced by environmental factors. This abnormality makes the chance of finding it rare, about 1 in 5000. Due to the genetic abnormality, finding a four-leaf clover is rare.
 Gnostotheca 9108