Those are Japanese Maple leaves (one of my favorite trees) and can be made of gumpaste. Just make sure that you use thin wire.
This cake is from Brides Mag "50 Most Beautiful Cakes" and the copy in the mag states that the leaves are indeed gumpaste. Although they look too thin and would be exceedingly fragile if actually sugar.
The cakes are online at Brides. com According to the article, the bands aroumd the tiers are spun sugar.
Thanks everyone! What a big help that you found that picture online. The bride wants to use silk flowers to save money. I've no idea where she will find them.