Well, I don't know about rooting any and or all leaves....I do know ( from experience ) that violets are very easy to root from a leaf. When one gets "accidentally" ( by dogs usually) gets knocked off. I trim the stem to about an eigth of an inch from the leaf. You can put in directcly in soil.....keep moist and under a plastic bag, I don't seal mine tight, I just check it each day, or you can put tin foil over a small glass. Like a shot glass or an coffe cup, cut a slit in the tin foil and push the remaining stem into the water. I try and keep my water level where the leaf edge meets the stem, not at the bottom of the stem, or not half way up the leaf. Then the baby violet (takes about a month) will put itty bitty leaves and the joint of leaf and stemm. I've had really good results with this and have given almost all my babies away, because my friends are always saying.....ahhhh how cute, what an adorable lil violet. Then I think .....well, if they get into
flowers and gardening, I will get some of there "run overs". that hasn't happened yet ( except for family
plants) but most of my friends have several babies or rescued office
plants in their homes. It's nice to visit them, ( and my friends too) hahahaha
Hope this helped a lil bit!