Hydrophobic surface allows self-cleaning: sacred lotus
Leaves of the sacred lotus are self-cleaning thanks to nanoscale bumps.
"The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data...it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the 'Lotus-Effect' and which may be of great biological and technological importance." (Barthlott and Neinhuis 1997:1) Learn more about this functional adaptation.
Barthlott, W.; Neinhuis, C. 1997. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta. 202(1): 1-8.
Nature's Raincoats. Nottingham Trent University, University of Oxford.
Neinhuis, C.; Barthlott, W. 1997. Characterization and distribution of water-repellent, self-cleaning plant surfaces. Annals of Botany. 79(6): 667-677.