Floating lotus leaves retain their flat, circular shape thanks to the water that supports them.
The leaves of a young lotus (Nelumbo nucifera) lie flat on the surface of ponds and lakes, with only small ripples forming at the edge. But long stems often push the leaves of full-grown plants above the water’s surface. Such leaves typically have a wavy, warped appearance.
Fan Xu and his colleagues at Fudan University in Shanghai, China, modelled the physics of lotus leaves and found that those sprouting from long stems experience a critical amount of strain that causes the leaves to warp as they grow. But floating leaves experienced vertical support from the water, allowing them to stay mostly flat and to form wrinkles on only the edges.
The team confirmed these findings with experiments on sheets of rubber cut to the shapes of different leaves. When lying on water, the rubber leaves experienced only slight buckling on the edges. But when removed from water and suspended in the air, the entire leaf became warped.