The surfaces of leaves and shoots are covered by a thin extracellular membrane, the cuticle. It constitutes of an insoluble polymer (cutin) and soluble lipids, usually called "waxes". They are embedded into the polymer and are also present on the surface. In most plants, these epicuticular waxes form characteristic microstructures due to self-organisation. Generally they are regarded as crystals. The epicuticular wax layer is a multifunctional interface between plant and environment, influencing air flow or light reflexion and often causes high water repellency. Water which is applied to such surfaces forms small droplets rolling free over the leaves. As a new, hitherto overlooked feature we were able to show that water-repellency is connected to an almost perfect self-cleaning ability of leaves. Since this effect can be beautifully demonstrated with the large peltate leaves of INelumbo nucifera/I, the sacred lotus, we called it Lotus-Effect. The Lotus-Effect is present in a large number of plants and depends on microstructured hydrophobic surfaces. While in smooth surfaces contact angles reach up to 110°, roughness in the dimensions of micrometers causes super-hydrophobicity with contact angles up to 170°. In such cases the area for adhesion for water is minized and air is enclosed between droplets and the individual wax crystals. The same holds true for particles. Again, the contact area between particle and rough surface is minimized resulting in the adhesion of particles to the water droplets that roll over the leaf surface. Independant of size and chemical nature, particles are removed from such super-hydrophobic surfaces with only a small amount of rain. Since the Lotus-Effect depends only on physico-chemical properties of the leaves it can be transferred to technical surfaces and may lead to biomimetic self-cleaning paints or other surface coverings in the near future.

Key words: contamination, cuticle, epicuticular waxes, Lotus-Effect, self-cleaning, wettability