Any filled or closed shapes you will create in Illustrator will not be the correct kind of geometry to curve into the third dimension in Strata. Filled or closed Illustrator paths are the same thing as a 2D Bezier region in Strata, which is by definition 2D, not 3D.
So, you will want to model the leaf in Strata. A Bezier surface is capable of being wrapped, or you could model a skin or hull surface directly in a curved configuration. A properly constructed polygon mesh or subdivision surface can be deformed to curve as well.
There is a very helpful thread on this subject on the StrataCafe: