What Makes Lotus Flower Leaves Water Repellent?

The lotus flower has a special or sacred place in world religions like Hinduism and Buddhism. It is a symbol of purity, and many a time gods are shown seated on lotus thrones. Now a group of German Scientists have discovered that the lotus plant is truly spotless. It does not allow any dirt to remain on its surface. And there is a clear reason for it.

Scientists say that these leaf surfaces have an amazing ability to clean themselves. Scientists at the University of Bonn carried out extensive research to show that the water droplets rolling off a lotus leaf carry away dirt particles leaving the surface perfectly clean. This phenomena has been named the ‘Lotus Effect’ and works best on rough surfaces. A report on the scientists’ study was published in the journal ‘Planta’.

Lotus leaves are round and large and it is almost impossible to get them wet. You may splash as much water as you want on a lotus leaf, but the droplets immediately roll off. What makes this water plant’s leaves water repellent? Scientists have always known that aquatic leaves secrete or give out wax crystals. These crystals help prevent the leaves from getting flooded with the water around the leaves. They also help the leaves retain the required amount of moisture. The leaves are able to do this because wax repels water.

Contrary to popular belief, lotus leaves are not smooth at all. When examined under a powerful microscope, the leaf cells show a bumpy surface. That makes the surface rough. As a result, dirt particles rest only on the tips of wax crystals coating the leaf surface. The roughness reduces the contact area between the particles and the leaf surface.

A rough surface structure with wax crystals makes it impossible for water to stick. Due to the friction, the water contracts at once. It forms spherical droplets to minimize the contact area with the rough, waxy leaf surface and runs off the leaf very quickly. Since the dirt particles only rest on the tips of the wax crystals they stick more strongly to the water droplets than to the leaf surfaces. They are washed away when the water falls on the leaves.

On smooth leaves, the dirt particles are pushed from one part of the leaf to the other. This is because the dirt particles have a larger contact area where they can rest comfortably on the flat surface. We must also keep in mind that water usually spreads and only partially runs off the leaves — that too, only if the leaf is tilted! The dirt particles may get dislodged, but they are mainly displaced from one side of the leaf to the other.

Scientists say that the Lotus Effect is particularly beneficial for it helps to protect the lotus leaves from harmful bacteria. The dirt particles on the leaves often contain tiny disease causing fungi and bacteria. While most of the bacteria get washed off, the few that remain eventually perish since they do not get the water they require for survival and growth. Ultrahydrophobicity and self-cleaning properties are also found in other plants, such as Tropaeolum (nasturtium), Opuntia (prickly pear), Alchemilla, cane, and also on the wings of certain insects.

Content for this question contributed by Jeannie Barber, resident of Tampa, Hillsborough County, Florida, USA