Lotus leaf self-cleaning ability is due to the roughness of its surface at micro and nano level. The micro relief of plant surfaces, mainly caused by epicuticular wax crystalloids forming bumps, serves different purposes and often causes effective water repellency.

Each lotus leaf surface is covered with an array of tiny bumps. This uneven surface is itself covered with waxy hydrophoci crystals. The two-tier roughness on leaf’s surface minimises the contact between the solid surface and waterdrops.

Source: ForumIAS