Sorted

I have come up with a design that allows the stem of the second blackwork leaf to go downwards without it having to be so steep that the shading doesn't work:

The leaf has become virtually horizontal with just a very slight downward curve at the end which is enough to keep it looking realistic. I am using a vertical pattern under the stem and a horizontal one above it again to keep the two leaves balanced without symmetry, but this time the shapes in the pattern are larger so there are more stitches in the centre of them that can be taken out for the lighter section.