Life as a small plant can be tough. Larger competitors hog the sunlight, leaving shrimp species to photosynthesize from any seeping waste. But at least one ground person has come up with a solution that many of us shorter humans have probably at least fantasized about: pushing those lanky neighbors out of the way.
The find, reported earlier this year in the journal Current Biology, is the first documented case of interspecies push in the botanical literature, said Peter Grubb, a professor emeritus of botany at Cambridge University who is not involved with the research was. The study authors, Dr. Grubb, said, “are the first people to make relevant measurements of blade thrust.”
The intrusive leaf in question belongs to the impressively named large elephant’s foot or Elephantopus elatus. The plant is an aster that sends out long, flat leaves from a central stalk in a circular pattern known as a rosette. The foliage can form dense mats on the forest floor of pine savannas in the southeastern United States.
“People think it’s all grass down there,” said Camille Sicangco, who completed research at the University of Florida before receiving her bachelor’s degree in May. “But if you take the time to look a little closer, you’ll find that there are many different forms of growth.”
Ms. Sicangco, who will next study botany at Western Sydney University in Australia, and Francis “Jack” Putz, a botanist at the University of Florida, plucked some elephant feet from a savannah near Dr. Putz’s home on the outskirts of Gainesville and transplanted her to his lab. Ms. Sicangco then worked with engineering professors at the university to design and 3-D print a ground-mounted cantilever system that growing leaves could push against.
The researchers placed the device next to a growing plant and left it there for 24 hours. When they returned, the blade had pushed the lever away from its initial vertical orientation. In a series of experiments, the scientists measured an average thrust force of about 0.02 newtons – about the force required to lift one cent. That’s about as strong as the force a real elephant can muster compared to the tiny weight of the blade. The thrust came from hydraulic pressure generated in plant cells, Dr. plaster.
Next, the scientists raised the aster near some vigorous rye seedlings. As the Elephantopus leaves grew outward, their outer edges would sometimes curve downward, creating surfaces on which the plant could bend and choke up to 20 blades of grass. Collectively, the spreading leaves of a single plant took up up to a square foot of soil.
dr Putz and Ms. Sicangco weren’t the first to speculate about intrusive plants. Karl Niklas, a botanist emeritus at Cornell University, suggested this possibility years ago in a book he was writing on plant biomechanics. “But,” said Dr. Niklas, “talking about it and actually documenting it are two different things.”
The finding contradicts the general view that plants are indolent and peaceful, he added. While most people “think plants are kind of pretty and passive, just sitting there,” he said, plants actually “manifest a number of strategies that illustrate aggression.”
The elephant foot aggressive style could be widespread. The rosette growth form is found throughout the world, from the fynbos scrublands of South Africa to the dry grasslands of Australia and the prairies of the Midwestern United States. It’s even found in common weeds like dandelions and plantains, the bane of suburban homeowners striving for the perfect lawn. Low growth can help keep these plants from being nibbled by grazing animals, topped by lawnmowers, or consumed by fires, said Dr. Plaster – and pushing, he suspects, is probably practiced by many.
“Once you’re aware of it, it’s pretty obvious that it’s happening everywhere,” he said. “It’s in your backyard.”
The behavior could even help ecologists investigate a long-standing mystery: how do so many plants coexist in natural ecosystems? In prairies and savannas, plant species often maintain an exquisite balance, with dozens of species sharing a few square meters of space. Ecologists debate why strong competitors like fast-growing grasses don’t just take over. Pushing could be part of the answer, said Ellen Damschen, an ecologist at the University of Wisconsin-Madison who studies savannahs similar to those where large elephant feet grow.
“This pushing behavior likely helps it gain and maintain a foothold in the larger ecosystem,” said Dr. ladies.
Though she’s never observed plant pushing, she said she wasn’t too surprised to learn about it.
“Plants can do a lot more than we often think,” she says. “We just don’t give them enough credit.”