A common houseplant hides a pattern that may reveal how some leaf veins form.
The leaves of the Chinese money plant (Pilea peperomioides) display a geometric pattern called a Voronoi diagram, researchers report May 12 in Nature Communications. That pattern may form as waves of a plant hormone spread from tiny water-secreting pores and meet during the leaf’s development. A similar mechanism may also shape vein patterns in other plants, the researchers say.
“This is a beautiful new extension of the principle that veins are optimizing across so many functions and have so much to tell us,” says Lawren Sack, a plant biologist at the University of California, Los Angeles, who was not involved with the work.
The pattern was discovered when Elijah Blum, then a high school intern at Cold Spring Harbor Laboratory in New York, noticed the Pilea’s fascinating leaves while plant-sitting for his sister. The leaves were speckled with water-venting pores called hydathodes, each fenced in by veins to form a mosaic. Blum, now at New York University, took the plant to his supervisor, computer scientist Saket Navlakha.
“He showed the plant to me, and he said, ‘Look, the veins look kind of interesting here,’” Navlakha says. “And we sort of held it up to the light, and we saw that canonical Voronoi diagram.”
In a Voronoi diagram, a surface is divided around a set of points so that every spot in a zone is closer to that zone’s point than any other. Urban planners use the same idea to map services such as fire departments, assigning houses to the nearest station.
Voronoi-like patterns appear elsewhere in nature, including in the tiling of giraffe fur and the scales of dragonfly wings. But in a true Voronoi diagram, the mosaic must be generated by a set of points. In the Chinese money plant, the hydathodes serve as those points. Using geometric and statistical tests, Navlakha, Blum and their colleagues determined that the pores’ relationships with major veins satisfy the conditions of a Voronoi diagram.
The team then looked for how the pattern might develop. The conventional explanation for how similar leaf veins form is canalization, in which the plant development hormone auxin branches out across leaves to create a treelike network of channels that become veins. But canalization wouldn’t produce a Voronoi relationship with hydathodes. Computer simulations instead suggested that as Pilea leaves develop, auxin waves radiate from each hydathode, colliding to form fronts that eventually become major veins.
Mathematical biologist CiCi Zheng, formerly at Cold Spring Harbor Laboratory, says more research is needed to determine why Pilea leaves follow this pattern. One possibility, she says, is that the Voronoi pattern keeps major veins, which transport water, as far as possible from hydathodes, where water loss peaks. “You might want to place the veins not directly close to any of those locations where water evaporates super fast,” says Zheng, now at the Allen Institute in Seattle.
Sack is excited about what the finding could mean beyond plant biology. Previous studies of leaf veins, he says, have helped improve technologies such as solar panels, electronic circuits and irrigation systems by getting engineers to reimagine how distribution systems can be optimized.
“The more we know about leaf veins,” Sack says, “the more we can build functional and beautiful systems around us.”
