Ethan Gutmann at Ars Technica writes about the remarkable properties of rose petals when water drops land on them. Not only are rose petals superhydrophobic, like many plant leaves (water drops ball up on the surface), but unlike those leaves, those cool water drops also stick to the surface rather than rolling off.
What makes that happen is the microscopic structure of the surface of the leaf. The petal surface is covered in tiny bumps, and the surfaces of those bumps are covered in even smaller, tiny tiny folds. But those tiny tiny folds are far enough apart that water at the bottom of a drop can get into them and stick to the surface; on most leaves, the folds are closer together, so the water can't stick and slides off.
Here's the research paper.