Trifolium Repens -- What it means.

A four leaf clover refers to an aberration of a three leaf clover plant, the Trifolium repens or "white clover."

The white clover is a deep green flowering vine with white blossoms. It is the original shamrock plant of Ireland and the unofficial state symbol. The shamrock already has powerful associations, and its occasional production of an extra leaf makes the rare four leaf clover especially lucky.

One leaf stands for faith, another for hope, the third for love and the last for luck.

Many myths are associated with four leaf clovers. Finding one not only brings good luck, but in the Middle Ages, it was also thought to allow the bearer to see fairies and plant sprites. So it was that children often searched fields for a four leaf clover in order to see into the magical realm of the spirit world.

A genuinely rare, four leaf clover from Trifolium repens will usually have a smaller fourth leaf in comparison to the others on the stalk.

If you find a four leaf clover you can consider yourself very lucky indeed.

Source: http://www.wisegeek.com/what-is-a-four-leaf-clover.htm