Intelligence is an elusive concept, which challenges our definitions and our certainties. Traditionally associated with the presence of a central nervous system, it is now being questioned by more and more studies. The latest concerns a plant, known as Goldenrod (Solidago altissima), which appears to demonstrate surprising cognitive abilities. According to researchers, in fact, this species is able to perceive the danger signals emitted by its peers under attack, and also to modify its behavior to prepare to face the threat. A discovery that pushes us to question the nature of intelligence and the multiple forms that it can take in living things.
Communicating without a nervous system: Solidago's secret code
Solidago altissima, a common herbaceous plant in North America, is the focus of a recent study published in the journal Plant Signaling and Behavior (I link it here). Researchers Andre Kessler, a chemical ecologist at Cornell University, and his Ph.D Michael Mueller, they discovered that this plant is able to "listen" to the danger signals emitted by its neighbors attacked by herbivores, and to react accordingly.
When the beetle larvae begin to feed on the leaves of the Solidago, the plant emits volatile organic compounds (VOC). These are compounds that signal to insects that the plant is damaged and that they should look for a better food source. At the same time, the plants attacked they also change the reflection of red light from their leaves, a signal detectable remotely by other plants. Both the light and the chemical compounds appear to serve as private, distant warnings of imminent danger to other Solidagos in the vicinity. Only related neighbors with the right “understanding” can decipher the code embedded in VOCs.
An “intelligent” response to danger
In response to these signals, nearby Solidagos strengthen their defenses against predators, growing faster and producing defensive compounds to fight off insects, similar to an immune system. According to Kessler and Mueller, this behavior is not a simple reflex or fixed pattern of action, but a "considered" behavioral change, based on the costs of herbivory and peer competition. In other words, Solidago does not always react in the same way, but adapts its response based on the information it receives from the environment.
Depending on the information it receives from the environment, the plant changes its standard behavior. Given this definition and the accumulating evidence, the question is not whether plants express intelligent behavior, but how they achieve it without a nervous system and what the ecological consequences of these behaviors are.
Andre Kessler
Plant intelligence, very open debate
The idea that plants can exhibit “intelligent” behavior is still controversial in the scientific community. Many researchers are reluctant to attribute terms like “intelligence” or “cognition” to organisms without a central nervous system. However, the Solidago study is part of a growing body of research suggesting that plants are capable of sensing, learning, making decisions and communicating in much more complex ways than previously thought.
As early as the 80s, scientists discovered that some plants use VOCs to privately “talk” to their neighbors about common threats. Since then, numerous studies have investigated the sophisticated chemical communication networks in the plant world. What makes the study on Solidago particularly interesting is the idea that these plants not only communicate, but do so in an "intelligent" way, integrating information from the environment and modifying their behavior accordingly.
This obviously does not mean anthropomorphizing plants or attributing human characteristics to them. Rather, it is about recognizing that intelligence can manifest itself in different and unexpected ways, and that the plant world could still reserve many surprises for us.
