Why not extrude the flat leaf and then use CageEdit to curl the leaf more realistically?
Here is what I came up with in a minute or so of fooling around:
To make it, I traced a bitmap with a curve and extruded it to create a flat leaf. I then drew the two curves you see along the dimensions I wanted the leaf to curl, clicking the control points where I thought I might like to grab. Issue the "CageEdit" command with the leaf, one curve at a time, and Global region, and off you go to the races.
Does that work?
Probably lots of ways to do it in Rhino...