What a huge water lily can teach us about building design


The giant Amazonian water lily has long fascinated scientists, architects and artists for its beauty and size. Yet how the leaves of the lily can grow to a size of 10 feet in diameter, strong enough to support the weight of a small child, has remained a mystery⁠ – until now.

A team of British and French scientists studying the mechanics of these giant sheets have documented a network of branching beam-like veins optimized for strength and structural support. Their research, published in February in Scientists progresscould transform this Chris Thorogoodthe deputy director of the Botanic Garden & Arboretum at the University of Oxford, calls “a great botanical enigma” a guide that could inspire better engineering and design in buildings, especially in floating structures.

“What we’ve shown through our empirical experiments and mathematical modeling is that these sheets are particularly tough and have a rigid flexibility that allows them to get really big,” says Thorogood, who was lead author on the paper. ‘study.

inspiring veins

From above, the leaf of an Amazon water lily looks like a large green plate with an upturned edge. The source of its beauty and strength is seen only from below.

“When we pull the leaves out of the pond here and the audience sees them, they actually gasp at the beauty of the leaves,” says Thorogood. “They are incredibly beautiful.”

The underside of the leaf is entirely covered with a fractal network of spiny veins that radiate from the central stem. The main veins thin out and branch off as they approach the edge of the leaf. They are crossed at regular intervals by other veins which form concentric circles and are specific to this type of water lily. The overall effect is striking: an intricate network of yellow veins set against the dark green or red of the leaf. (There are two sister species of giant water lilies with different colors on the underside.)

The giant lily was discovered by British explorers in South America in 1801. It quickly gained popularity in Victorian England, where its genus name, Victoriawas given in honor of the young Queen Victoria, and the plant became a symbol of the British Empire.

But it has become more than a symbol as botanists have repeatedly attempted to cultivate it in captivity. “It was an obsession”, writes Tatiana Holloway in her book, The Flower of the Empire. “Absorbing some of the most eminent and enterprising men of the Victorian era, the effort to recover this peerless exotic from the equatorial wilderness where it grew and cultivate it in England has become an epic quest that has captivated the world. .”

British gardener and architect Joseph Paxton was the first to successfully grow the giant water lily. He inspired his design for the Crystal Palace, a cast iron and glass London landmark that was built for the Great Exhibition of 1851 (and later destroyed by fire).

“Nature was the engineer,” Paxton said in an 1850 address to the Royal Society of Arts. “Nature has endowed the sheet with beams and longitudinal and transverse supports which I, borrowing from it, have adopted in this building.”

Paxton had an intuitive understanding of the Lily’s forces, but it was only now that Thorogood and his colleagues worked out the mechanical details.

Put a sheet to the test

Wearing waterproof waders, the researchers climbed inside the large heated pool at the University of Oxford Botanic Garden to experimentally measure the leaves’ response to weight.

“Oh my God, I was looking for this opportunity to climb into a pond and poke a lily pad,” says Finnish box, a fluid mechanics researcher at the University of Manchester and lead author of the study. “It was very fun.”

To grow to a size of ten feet in diameter, far larger than any other water lily, the Amazonian water lily must be strong. The leaf tissue between the veins is only about a millimeter thick. The water on which the leaf floats supports its weight, but it must withstand the rainfall of a tropical storm or the weight of a bird flying through it without being shredded and submerged.

“Once a leaf is submerged, it will lose its space on the surface where it can perform photosynthesis,” Box explains.

The secret of the Amazonian water lily is its prominent vascular system, a biological innovation that smaller water lilies lack: they look like flat disks with thin, barely noticeable veins.

Box and his colleagues measured the lily’s strength through a series of stress tests. First, they detached a meter-long lily pad from the stem by anchoring it in the mud below and dragged the sheet to the edge of the pond. They carefully avoided the fierce centimeter-long spines that cover the underside and protect the leaf from nibbling fish.

With a camera, they recorded how indented and distorted each sheet was when pressed or placed weight on it. These strength tests showed that Amazonian lily pad leaves were an order of magnitude stiffer and, therefore, stronger than the smaller leaves found on other more common lily species.

Using computer models and a 3D-printed test sample, the research team tested their hypothesis of how Amazonian plants do this. They found that the branching veins of the giant lily, which start very thick near the center and taper towards the edge of the leaf, evenly distribute the weight of the leaf. They stiffen and support the sheet while allowing it to spring back elastically when deformed, for example, by a bird’s foot – and they do this very effectively.

What is there for the water lily and for us

The Amazon water lily thrives in seasonally flooded parts of the Amazon basin, where it has about six months to grow before the water disappears again. During this period, its large giant leaves allow it to absorb as much sunlight as possible.

The veins surrounding the leaves essentially allow the water lily to cover more area for photosynthesis while using less biomass. By comparison, the regular leaves of smaller common lilies simply couldn’t support that much weight.

“The larger your surface area, the more photosynthesis you can do,” Box says. “This economy between plant matter and photosynthetic capacity is obviously important to them.”

Humans have already developed plant-inspired biomimetic applications, like the velcro of burdock plant burrs and the self-cleaning surfaces of lotus leaves. The insight of a big floating leaf isn’t so far-fetched; in addition to improving the design of floating structures, it could unlock profitable new designs for offshore wind turbines or even floating “seastead” companies. In 2008, Belgian architect Vincent Callebaut designed a floating city based on the structure of the giant lily leaf called “Lilypad—a floating ecopolis for climate refugees.

“Maybe the thing that we engineers can relate to is, ‘Hey, has anyone ever thought about branched beams or beams that have varying cross-sections?’ asks Box. “I suppose you may have made progress when you have to go back to your own world and think about some of the things you encountered while you were in the biological world.”

There’s something poetic about the idea of ​​humans one day using solar panels floating placidly on a platform inspired by Amazonian water lilies to collect as much sunlight as possible, just as the plant has done for millions of years. years.

“It’s a similar idea,” Box says. “So why can’t we learn from natural examples that have developed an optimal solution?”

This story has been corrected to acknowledge that there are two sister species of Amazonian water lilies, amazon victoria and the little bit smaller Victoria Cruziana.


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