Tamara Bonnemaison is the author of today's entry. She writes:
Thank you to apasar@Flickr for these two lovely photos of Nelumbo nucifera or sacred lotus (do browse apasar's photostream for additional photographs!). The sacred lotus has been featured briefly once before on Botany Photo of the Day in this entry: Nelumbo nucifera.
The sacred lotus is one of only two species in the Nelumbonaceae, and can be found growing wild from southern Russia to northern Australia. The other species in this small family is Nelumbo lutea, which grows in eastern and southern North America. Up until fairly recently, the Nelumbonaceae was placed in the Nymphaeaceae, or water lily family. Recent molecular studies have shown that the sacred lotus is not closely related to water lilies, and that its closest living relatives are instead the plane trees (Platanus spp.). It is now believed that the similarity of lotuses to water lilies can be explained through convergent evolution, meaning that they independently evolved similar traits because they occupied similar environments. Nelumbonaceae now constitutes its own family, and can be easily identified by its leaves and flowers that are raised above the water on stalks, as opposed to the leaves and flowers of water lilies, which float on or below the water's surface.
The sacred lotus has a long history of use, and is sacred to Hindus and Buddhists, symbolizing beauty, purity, fertility and divinity. There is an abundance of literature, folklore, and imagery available about the sacred lotus, which makes it both easy and difficult to write a short entry about. What to cover, what to leave out?
A short botanical description seems in order. Nelumbo nucifera is an aquatic perennial with beautiful, showy flowers. Its rhizomatous roots anchor to mud in shallow water bodies, and its leaves are held above the water on long stalks that join the round leaves at the centre of the blade (this leaf attachment is termed peltate). The flowers come in white, pink or slightly yellow, and are held above the leaves for a period of two days, closing overnight. At the base of each flower resides an unusual spongy receptacle that is obconical and truncate in shape. Apasar's close-up shows the yellow receptacle beautifully; the strange "googly eyes" are the many separated ovaries bearing sessile stigmas embedded just below the truncated top of the receptacle. One final note - sacred lotuses are extremely long-lived, with individuals living upwards of a thousand years. Seeds can remain viable for an even longer time period.
Of the many cultural, spiritual, scientific and horticultural aspects of this species that I could highlight, the one that strikes me as particularly fascinating today is the "lotus effect". The sacred lotus grows in mucky, swampy environments, yet its leaves emerge from the water perfectly clean. This characteristic drove Buddhists to revere the sacred lotus as a symbol of purity, and now drives engineers to study it in order to develop substances that mimic its self-cleaning mechanisms. The development of high-resolution electron microscopes in the 1960s allowed researchers to study the nanostructure of leaf surfaces, and since that time a clear picture of how plant surfaces self-clean has emerged. The sacred lotus, and other self-cleaning species, have surfaces that are superhydrophobic, or extremely water-repellant. Although a lotus leaf appears waxy and smooth to the naked eye, it is actually covered by microscopic bumps that minimize the point of contact between the leaf's surface and the water droplet, allowing the water droplet to roll off the leaf's surface even at very low angles, picking up dirt and other particles along the way. All of this is achieved through the structural surface of the leaf, and is explained very well in the article, "The Dream of Staying Clean: Lotus and Biomimetic Surfaces" (PDF).
These same principles are now being applied to engineered surfaces to create paints, clothing, building materials and other objects that are water repellant and self-cleaning. Lotus-like nanosurfaces can now be found on the inside of ketchup bottles (to get out the last drop of ketchup) and on the outside of buildings (to keep the building clean and free of mold). Use of the lotus effect is a great example of biomimicry, which is "an approach to innovation that seeks sustainable solutions to human challenges by emulating nature's time-tested patterns and strategies. The goal is to create products, processes, and policies--new ways of living--that are well-adapted to life on Earth over the long haul". See biomimcry.org for more.