What plants can actually do
Start with the behavior, because it is more impressive than most people expect. A root tip explores the soil, sensing gravity, moisture, nutrients, touch, and chemistry, and steers its growth toward what it needs while avoiding salt, toxins, and obstacles. A plant under attack by caterpillars releases airborne chemicals that prime its own undamaged leaves and can even alert neighboring plants to raise their defenses. Climbing plants find supports; some track the sun across the sky; a Venus flytrap counts insect touches before deciding to snap shut.
The botanist Anthony Trewavas has argued for years that this deserves to be called intelligent behavior, provided we judge a plant on its own terms rather than expecting it to act like an animal. A plant cannot run, so it computes with growth: it integrates dozens of environmental signals and reshapes its body and chemistry to compete and survive. By that working definition (flexible, goal-directed behavior tuned to circumstances) plants clearly qualify.
The learning controversy
The harder question is whether plants learn and remember. The most famous experiments come from Monica Gagliano. In a 2014 study she repeatedly dropped potted Mimosa pudica, whose leaves fold when jostled; the plants stopped folding once the drops registered as harmless, and appeared to retain that habituation for weeks. She later reported that pea seedlings could be trained to associate a fan with the direction of light, an apparent case of Pavlov-style associative learning.
These results are exciting and genuinely contested. Some labs have had trouble reproducing the associative-learning result, and critics led by the plant physiologist Lincoln Taiz argue in a widely cited 2019 paper that plants 'neither possess nor require consciousness' and that terms like learning and cognition are being stretched past the evidence. The fair verdict today: habituation-like effects in plants are real and repeatable, but strong claims of associative learning remain unproven and need independent replication.
Intelligence without a brain, or a metaphor stretched too far?
Underneath the data sits a definitional argument. Researchers such as Paco Calvo and Miguel Segundo-Ortin hold that cognition is a broad biological toolkit for sensing and responding adaptively, and that plants sit comfortably inside it. Skeptics reply that plants lack neurons, brains, and any known mechanism for subjective experience, so calling them 'intelligent' risks confusing sophisticated physiology with a mind.
Both sides largely agree on the biology and disagree on the words. What is not in doubt is that plants sense and process far more of their world than the old image of passive greenery allowed. Whether that adds up to 'intelligence' depends on how you define the term, which makes this a question about mainstream cognitive science as much as about botany. And there is no evidence that plants feel pain or have inner experiences, so the wonder here is in the biology, not in anything unsettling.