Scientists at Cold Spring Harbor Laboratory in New York recently discovered that the Chinese money plant (Pilea peperomioides), known for its coin-shaped leaves, naturally arranges its vein networks into a Voronoi diagram.
A Voronoi diagram is a mathematical method that divides a space, like a map, into specific regions based on distance to a set of points. We’ve been using it for decades – meteorology, biology, medical diagnosis, urban planning and even art history.
This is not the first time we’ve seen a pattern resembling a Voronoi diagram in nature – for example, it can be observed in giraffe skin patterns or secondary veins of dragonflies. The difference is, nature’s versions of the diagram don’t usually contain the obvious central points you might encounter in a math textbook. The Chinese money plant is a rare exception.
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This plant species occurs only in the Sichuan and Yunnan provinces in China. It grows on shady, damp rocks in forests at quite high altitudes (1,500-3,000m). It’s endangered in its native habitat, but kept as an ornamental plant worldwide.
How the Chinese money plant arrived in Europe from Asia is quite an interesting story. It was first collected by George Forest in 1906 in Yunnan, China, and rediscovered and brought back to Norway in 1946 by Norwegian missionary Agnar Espegren. He then started travelling around the country and giving sprouts of the plant to friends – subsequently spreading it all around Norway, Sweden, England and beyond.
The Chinese money plant became popular on social media in the late twenty-tens. Today, it’s sold by most big retailers, but before it got famous, you could only get it from personal growers for substantial amounts of money.
The plant’s circular leaves contain pores called hydathodes, surrounded by looping vein networks which move water and nutrients through the leaf. It’s those pores and veins that helped associate professor Saket Navlakha and former graduate student Cici Zheng find the math secret within the plant.
"Just as humans have to solve problems to survive, the same goes for other organisms," says Zheng. "But unlike humans, plants cannot explicitly measure distances! Instead, they rely on local biological interactions to achieve the same Voronoi solution."
The scientists behind the discovery have emphasised that these natural algorithms can be seen as “a way to try to make sense of the world.” These findings might be the key to understanding the still under-researched mystery of leaf vein formation, and the intricacies of how exactly plants solve biological challenges.
Read the full findings in the original paper published in Nature Communications.
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Top image: Pilea peperomioides houseplant known as Chinese money plant. Credit: Dmitrii Marchenko/Getty Images
