
Sunflowers move in a way that helps their neighbours. The seemingly random motion of the plants’ roots and shoots actually minimises shade cover in crowded environments, ensuring that all of them get enough light to grow.
èƵs have known about this plant motion, known as circumnutation, for centuries, but its purpose has always been elusive. “In climbing plants, it’s clear that it’s a search process, searching for a new stick to twine on. But in other plants, it’s not clear if it’s a bug or a feature,” says at Tel Aviv University in Israel.
To find out more, Meroz and her colleagues grew sunflowers in a dense row and observed their motions over the course of 10 days, then created a computer model to quantify the movements. This showed that, as the plants twisted and turned, their growth gradually became optimised in such a way that all of them would get as much sunlight as possible.
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“Adding this noise, this randomness in movement, seems counterintuitive because noise can lead to unwanted states,” says team member at the University of Colorado, Boulder. “But in this case, it’s really important and can bring us closer to a more optimal configuration.” Once the plants reach a zigzag configuration in which each of them is getting enough light, their movement decreases.
Many plants go through motions similar to those of sunflowers, so this is a hint that all of them may be able to optimise their growth to fit their surroundings, says Meroz. “These circumnutations might be a way of exploring the plants’ environments and comparing signals in different places in order to identify the best growth strategy – which is pretty cool because we don’t think of plants as navigating or doing anything smart,” she says.
Physical Review X