The Guardian Our notions of clean and dirty are very traditional. Smooth surfaces are easy to keep clean and rough surfaces with lots of crevices and interstices harbour dirt. In an important way, we now know that this is wrong. Nature abounds in self-cleaning surfaces and they achieve this by being bumpy. Most people will have noticed a globule of water sitting on a leaf, glistening like mercury.
Lupins show the effect well.
If you have ever noticed this you were a hair's-breadth away from making a major scientific discovery. Because self-cleaning plants employ a mechanism that can be mimicked in paints and other surface coatings. The phenomenon is called the Lotus Effect. Its leaves never seem to get dirty unless interfered with by human beings, by spraying detergents on them for instance. Any dirt that attaches during dry spells is carried off by rainwater.