It's been a while since I piped something plant-related (what can I say, I prefer critters and hats). It's also been a while since I piped a truly simple project involving only one tip: leaf tip #69 (or any size you prefer). You'll also need a dusting pouch filled with a 50/50 blend of cornstarch and powdered sugar, a glue stick, parchment paper squares, a flower nail, and a Styrofoam block to rest the nail in. Start by sticking a parchment square to the flower nail with a dab from the glue stick.
When you place them on a cake, you may want to pipe vines first, perhaps with a round #3 tip. This is a cake from an earlier project:
Of course, you could pipe ivy leaves in black or dark purple to be totally goth.