I know that you have to use a firm leaf in order to make the chocolate leaves, like lemon, camillia or rose leaves.
Here's a how to with recipe:
this is the part you need..
Make chocolate leaves:
Line small baking sheet (or large plate) with foil. Add enough hot water (125°F. to 130°F.) to 9-inch-diameter cake pan to measure depth of 1 inch. Place 6 ounces finely chopped milk chocolate in 3- to 4-cup glass bowl; place bowl in hot water. Let stand just until outer edges of chocolate melt. Stir until chocolate is partially melted (some soft pieces will remain). Transfer bowl to work surface and stir until chocolate is melted and smooth and instant-read thermometer registers no higher than 88°F. (barely lukewarm). If melted chocolate is warmer than 88°F., add 1-inch piece of milk chocolate and stir until temperature falls below 88°F. Remove any remaining piece of chocolate.
Hold 1 leaf with heavily veined side up. Using pastry brush, carefully coat upper surface completely with chocolate. Using fingertips, wipe away any chocolate overflow from edges of leaf. Place leaf, chocolate side up, on prepared baking sheet. Repeat with 7 more leaves. Refrigerate coated leaves until chocolate is cold and set, about 10 minutes.
Carefully peel lemon leaves off chocolate leaves; return chocolate leaves to baking sheet and refrigerate.
Line another small baking sheet (or large plate) with foil. Melt 6 ounces white chocolate and make 8 white chocolate leaves, following technique and temperature guidelines for milk chocolate leaves.
Line another small baking sheet (or large plate) with foil. Melt 6 ounces bittersweet chocolate and make 8 bittersweet chocolate leaves, following technique for milk chocolate leaves. (Chocolate leaves can be prepared 2 days ahead. Keep refrigerated.)
Hope this helps!