The following steps show a few typical mutants so you know what you are looking for.
The Classic 4-leaf clover has, well, 4 leaflets. Most mutants have three leaf stems in which one has split into two leaves, one usally smaller than the other. These types are probably produced by evironmental factors more than genetic factors (not that genes don't play a part). Clovers with 4 leaflets, evenly shaped, and 4 seperate leaflet stems are, from my experience, rarer, and probably strongly genetically influenced.
Note: There are a few companies that have tried to breed 4-leaf clovers to sell for their alleged lucky properties. Due to the complications between environmental and genetic influence, these breeds are tough to produce, and only marginally effective, or so i've read. heres
one of these companies.