One of the best small leaf fig species to use for bonsai is the Willow Leaf fig, scientifically called Ficus salicaria. It has many great features including aerial roots and wide-spreading surface roots. One possible issue is that it does not like having roots that stay too wet. Water the tree well and make sure to allow the soil to nearly dry before watering it again. Continually wet roots leave room for fungal and other rot problems.