On a peaceful summer morning, a field of poplar trees stands calm, the breeze rustling their leaves. Insects flit from branch to branch, buzzing through the air. But beneath the surface, these trees are under siege as hungry insects devour their leaves.
While trees can’t flee or hide, they’re not defenseless. As soon as an insect begins feeding, the tree activates its defenses and sends an urgent message to neighboring trees: “Prepare yourselves, we’re under attack.” In some cases, the trees may even call on other insects for help.
This complex system of communication and defense, however, happens in ways we can’t see. And as scientists delve deeper into plant behavior, they’re uncovering remarkable abilities in plants—things we once thought only animals could do. Plants can communicate, form memories, learn from experience, and even recognize their relatives—all without a brain.
The Hidden World of Plant Communication
Simon Gilroy, a botanist at the University of Wisconsin–Madison, has spent years studying plant behavior. Despite their still appearance, plants are incredibly active. They communicate, often in ways that are far more intricate than previously understood.
Research into plant communication dates back to the 1980s when botanists discovered that plants can warn each other of danger. In a groundbreaking experiment, Jack Schultz and Ian Baldwin, then researchers at Dartmouth College, showed that when a tree’s leaves were damaged, it produced chemicals to repel attackers. The undamaged trees in the area reacted in kind within 36 hours, suggesting the injured tree sent a chemical signal through the air to its neighbors.
This finding, published in 1983, marked the beginning of a field of study on how plants communicate with each other. Since then, scientists have found that plant communication is far more sophisticated than initially thought.
For instance, plants respond differently to messages from close relatives than from unrelated plants, as Rick Karban, a plant biologist at the University of California, Davis, has shown. He also found that plants can distinguish between different types of predators and adjust their responses accordingly.
Plants can even signal the distance of danger. A recent study from Finland demonstrated that plants can assess how far away a threat is and adjust their responses accordingly. Furthermore, some plants send signals not just to warn other plants, but to attract predators that will eat the herbivores feeding on them. For example, tomato plants release a chemical to attract parasitic insects when attacked by hornworms.
The Role of Sound in Plant Life
While chemical signals are the most commonly studied form of plant communication, recent research suggests that plants also use sound. In 2023, researchers in Tel Aviv, Israel, recorded clicking noises made by stressed plants. These sounds, too high-pitched for humans to hear, are distinct for each species and are triggered by different forms of stress such as drought or physical damage.
Scientists have also found that plants respond to sounds, including the vibrations caused by insects munching on their leaves. Heidi Appel, a plant ecologist at the University of Houston, found that plants can actually “hear” the sound of these vibrations and react accordingly, preparing themselves for potential threats.
Learning and Memory in Plants
Plants don’t just react to immediate threats—they can learn from experience. One famous experiment in 2014 demonstrated this ability in Mimosa pudica, a plant known for its “sensitive” leaves. When dropped, the plant curls its leaves to protect itself. However, after repeated drops that caused no harm, the plants stopped curling their leaves. This suggested that the plants had learned the drop wasn’t dangerous, indicating they could form memories.
In fact, these plants retained this learned behavior for at least a month. This experiment, along with others, provides compelling evidence that plants can learn and even remember experiences.
A Nervous System, but No Brain
The question arises: How do plants communicate, learn, and remember without a brain or nervous system? Gilroy points out that all living organisms face similar challenges—finding food, water, and defending themselves—but plants solve these problems differently from animals. While animals rely on movement and a nervous system, plants have evolved their own solutions. They grow toward light, use chemicals to ward off predators, and even alter the soil to benefit themselves.
Plants may not have brains, but they do have systems that allow them to process information. Like animals, plants use neurotransmitters, such as glutamate, to send signals. When a plant is wounded, it releases glutamate to communicate with other parts of the plant, triggering a defensive response. Some scientists argue that this process is akin to the neural signaling found in animals.
Plants also rely on a sophisticated network of tubes, known as xylem and phloem, to move water, nutrients, and neurotransmitters throughout their bodies. This system acts like a nervous system, allowing plants to respond to their environment without the need for nerves or a brain.
Are Plants Intelligent?
Despite these remarkable abilities, the question remains: Are plants intelligent? Some researchers argue that they are, while others remain skeptical. The challenge lies in how we define intelligence. Elizabeth Van Volkenburgh, a plant biologist at the University of Washington, notes that while plants don’t have a nervous system, they do have a sensory system that allows them to respond to their environment in complex ways.
Others, like Rick Karban, believe that the debate over whether plants are “intelligent” is less important than understanding the full scope of their capabilities. “It’s more about what plants can do, how they interact with other organisms, and how they adapt to their environment,” he says.
Conclusion
Whether or not we label plants as “intelligent,” one thing is clear: they are far more capable and complex than we once believed. From communicating with neighbors to learning from experience and adapting to their environment, plants have developed extraordinary abilities to survive and thrive without a nervous system. As scientists continue to unravel these mysteries, they reveal a hidden world of plant behavior that challenges our understanding of intelligence itself.
Related topics: