I posted this picture a year ago today, showing a patch of clover that has an unusually high number of four leaf clovers in it.
The percentage in that little patch is just as high this spring, and I would have posted a picture, but a thunderstorm just before dawn left the patch beaten down and partially submerged.
I've tried to research the cause of this anomaly, with little success. The closest I've come is articles that say polydactyly in humans is due to an aberration in one of 26 genes. It appears to be random, and while it is not necessarily genetic, it does appear more frequently in people of African descent.