Nature

Lotus: more than just a pretty flower

Blooming lotus (Nelumbo nucifera) flowers are the focal point of lotus ponds and have long served as inspiration for brush painters and woodblock print artists in North Asia. Its significance extends from aesthetics to the spiritual as the habitat and physiology of the lotus have come to symbolise purity and enlightenment in Buddhism, one of the most practiced religions in Japan. Despite being largely unnoticed, other parts of the plant also serve a purpose – filling our stomachs for generations, helping researchers understand how plants regulate temperature and more recently, serving as inspiration for material science research.

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A blooming lotus flower surrounded by leaves.

Buddhism was first introduced to Japan in c. 550 AD and continues to be one of the most practiced religions in the country. The close relationship between aesthetic expression and religious worship in Japan is evident upon a quick visit to a temple – elegantly landscaped gardens surrounding temples create a sanctuary from the hustle and bustle of towns and cities. The commitment to quality and beauty is even more pronounced inside the temple, where only statues created by the best of artisans are on display.

Bentendo is a popular Buddhist temple in downtown Tokyo and together with the lotus, boat and cormorant pond that surround it, it’s commonly known as Shinobazu Pond. Despite Bentendo having a rich history that dates back to the Edo Period, the lotus pond attracts the most attention from tourists – the view of blooming lotus flowers rising above a sea of green is hard to match!

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Shinobazu Pond – view of the lotus pond with Bentendo in the background.

There’s more than mere visual attraction – the lotus has long been a symbol of enlightenment in Buddhism, where the muddy waters in which the plant grows represent the world of suffering into which all humans are born, the closed lotus flower represents a Buddhist’s path to enlightenment and the blooming lotus flower symbolises the final stage when enlightenment and purity of heart and mind is attained.

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A lotus flower in the early stages of its lifecycle.

The lotus flower generally blooms for only four days in the midst of summer. During this time, the flower opens and closes depending on the ambient temperature. Petals and stamen abscission begins by the end of the third day, marking the end of the pollination period. Such physical changes have been observed for centuries yet remained unexplained scientifically. Researchers have recently discovered the mechanism and reasons behind such changes.

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Lifecycle of a lotus flower – rows indicate days one to four, from top to bottom and columns indicate time at 6am, 9am, 12 noon and 3pm, from left to right. Source: Róbert Király

Researchers at the University of Adelaide have found that lotus flowers are able to regulate temperature within a narrow range of between 30 to 36 degrees Celsius. It does this by controlling the rate of heat production, which in turn is dependent on ambient temperature. For example, when the ambient temperature is low at night, the plant will contract its petals and increase heat production by converting more carbohydrates to energy through increased oxygen consumption and release of carbon dioxide. Conversely, the plant will decrease heat production during the day when ambient temperature is high.

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Birds eye view of a lotus flower during the first day of its lifecycle. The orange and yellow stigma and seed pod are surrounded by white stamen and enveloped by bright pink petals.

Attracting pollinator beetles and speeding flower development are speculated to be the key reasons lotus flowers engage in such behaviour. Beetles are naturally attracted to the warm confines of the closed lotus flower as the ambient temperature begins to fall at dawn. The warmth inside the closed flowers also allows beetles to feed and mate throughout the night. Rather than waiting for the sun to warm them up, beetles are covered in pollen by the morning and ready to start pollinating once the flowers open.

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Lotus flower during the last day of its lifecycle, marked by withering stamen, petal abscission and color change of seed pod. 

Lotus seeds begin to develop once the pollination process is over. The outermost layer of lotus seeds change from yellow-green to purplish-brown throughout the maturation process. The pericarp, consisting of three distinct layers that encase the lotus seed, serves as a water and air tight coating that protects the seed until the optimal germination conditions are met. Lotus seeds are renowned for its longevity, where seeds of more than 1,000 years old have been found and successfully germinated. The proteins, oils, nutrients and carbohydrates stored in the lotus seed provide energy for seed germination and also make it attractive to humans as a food resource.

All parts of the lotus plant have horticultural value and have a long history of being cultivated. Lotus seeds and rhizomes are very popular in North Asian cuisine, while lotus stems is a common vegetable in India. Although lotus leaves are generally not eaten, they are used to serve and wrap boiled or steamed foods.

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Lotus seed pod after abscission of petals and stamen.

Generally speaking, lotus leaves are round, grow up to 100cm in diameter and are supported by stalks of varying height and strength depending on the type of lotus leaf. The stalk is attached to the leaf at the centre leaf navel, from which veins radiate. Lotus leaves are weak and curled at the edges during the early stages of development and slowly uncurl as it matures. The upper side of the leaf is typically darker in colour and appears to have a waxy layer, while the underside of the leaf is a lighter shade and does not have a waxy layer.

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Young lotus leaf before it uncurls.

Although sparsely-scattered and healthy-looking lotus leaves are characteristic of picture-perfect lotus ponds, they do not tell the full story. When growth becomes dense, things get competitive. For aquatic plants, sunlight is the key limiting resource in performing photosynthesis, a process where plants convert carbon dioxide and water to glucose and other by-products in the presence of light energy. Of the three types of lotus leaves (standing leaves that rise above the water surface, floating leaves that rest on the water surface and underwater leaves that grow submerged), floating leaves and shorter standing leaves suffer from lack of exposure to sunlight when the standing canopy is dense.

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Floating lotus leaves under a canopy of standing lotus leaves. The floating leaves have an unhealthy appearance due to lack of exposure to sunlight.

How do the healthy leaves maintain such a clean appearance despite its muddy habitat? Bartlett and other researches discovered that the self-cleaning mechanism of lotus leaves are a result of water repellence, surface roughness and reduced particle adhesion. The water repellent nature of lotus leaves are largely caused by the waxy surface characterised by close yet irregular microscopic protrusions. This rough surface decreases the contact angle and further reduces adhesion forces between water particles and the leaf surface as it traps air between the protrusions and minimises surface area contact. Consequently, cohesion forces between water particles become relatively stronger as they roll off the leaf surface. Dirt particles stick to the surface of the water particles as they come in contact because the adhesion forces between the water particles and the dirt particles are stronger than the adhesion forces between the leaf surface and the dirt particles.

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Birds eye view of a lotus leaf – the dirt accumulated in the droplets of water demonstrate “The Lotus Effect”

Super-hydrophobic and self-cleaning qualities have since been coined “The Lotus Effect” and has important biotechnological applications in many fields; recent examples include anti-bacterial surfaces for use in the food production industry and mortar resistant to water uptake.

Lotus – a beautiful, symbolic, tasty and inspirational plant, from petal to root, through and through.

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