Thanks for the input! I went back and took another stab at it and ended up with this:
For reference, here is the "straight" image with no adjustment:https://picasaweb.google.com/lh/photo/EUDX47GstmZHXHPE-TASc9uMxvJiGcLBKZCCzrsb_KY?feat=directlink
The lighter shadows definitely help. They may still be a bit on the dark side, but I had trouble getting the leaves to pop as much as I wanted without losing the shadows.
Using a bit more digital manipulation than I typically like, and desaturating all but the center leaf also make a nice effect, though clearly no longer looks "natural." This one is attached.https://picasaweb.google.com/lh/photo/znQJbaZArEU7kIp0YvEui9uMxvJiGcLBKZCCzrsb_KY?feat=directlink