What causes some of the clovers to be four leaf? And others not to be?

Clover is a member of the pea family and some species are used by farmers to fertilize the soil.

When you find a normal three leaf clover, the three leaves are actually one leaf with three parts. This kind of leaf is called a segmented leaf. So, a four leaf clover has leaves with four parts instead of three.

According to Dr. Michael Vincent, who is a clover expert at Miami University, four leaf clovers aren't so rare after all. In fact, he has found hundreds of four-leaf clovers -- and even five-, six- and seven-leaf clovers on his lawn every year.

"The higher numbers of leaflets may occur if a young clover leaf is physically damaged, or exposed to certain chemicals. Or there can be genetic mutations in clover to cause multiple leaflets." http://www.earthsky.com/1996/es960317.html

The answer to your question about seeds of four leaf clover plants is a bit complicated. Firstly, damaging parent plants physically or with chemicals will not result in seeds that produce an abnormal number of leaflets.

However, if the quality of having four leaflets is in the genetic code of the parent plants (there has been a mutation), then the seeds of the plants will produce offspring with the same number of leaflets. Since I do not know the details about how leaflet number is determined genetically, I cannot say what would happen if a four-leaf clover was crossed with a normal three leaf clover.

http://www.madsci.org/posts/archives/may97/862164687.Bt.r.html

Thank you so much..great answer and links!