The scientific consensus is that plants do not have the kind of cognitive faculties necessary to support a consciousness that includes things like self-awareness, theory of mind, or complex emotions. That said, plants do have sophisticated mechanisms for sensing, perceiving, and responding to their environment. Plants do not simply sprout out of the ground, grow toward the sun, and hope for the best. If you watch houseplants for long enough and in a wide range of circumstances, it’s not uncommon to get the impression that maybe plants can think, maybe plants are self-conscious. With this in mind, here are some of the most critical and impressive aspects of plant perception that will help you appreciate the complexity of your houseplants, while also recognizing that houseplants cannot think as we do.
Proprioception: This is the plant’s ability to perceive itself in space. The plant knows if it sends off a growth shoot toward another part of its foliage, the two parts of the plant will connect and can be used for mutual support. The plant will also know where it still has room to grow. Proprioception also plays a crucial role in the plant’s ability to balance itself, while maintaining its other physiological processes. Humans also have proprioception, but this cognitive faculty is distinct from self-consciousness.
Geotropism: Also called gravitropism, this is the plant’s ability to sense gravity. Statoliths within specialized statocyte cells are denser than the surrounding cytoplasm and are sensitive to the force of gravity. But more than just knowing which way is up and which way is down, the plant shows a differentiated response. The plant roots are constantly trying to grow down with gravity, while the stems are constantly trying to grow up against gravity. More than just proprioception and geotropism, some plants can sense orientation and gradients to a degree that they have a fully formed sense of balance, or equilibrioception.
Photomorphogenesis: This is the plant’s ability to detect light and modulate its growth pattern. Again, the plant shows a differentiated response in which the roots are programmed to grow away from light, while the stems and foliage and programmed to grow toward light. This process begins as soon as the seed is germinated. A combination of phytochromes, cryptochromes, and phototropins also allow the plant to detect and respond to various duration, strength, and wavelengths of light. The plant has its own Circadian rhythm, internal clock, and seasonal adaptations. A related process, photoperiodism, detects periods of darkness to regulate when the plant produces its flowers.
Response to Other Stimuli: Space, gravity, and light are some of the most important and obvious ways that plants mimic behavior that can create the impression that plants can think. Even still, these are far from the only stimuli that plants can detect and respond to. Plants can also detect moisture, temperature, sound, touch, physical trauma, pests, and a wide range of chemicals in their environment. They can detect chemicals released by other plants and animals and release their own chemicals to repel unwanted pests and warn other plants that pests are in the area. They can communicate in a kind of common plant language.
Final Thoughts on Plant Consciousness
With these complex sensory and perceptual faculties, it’s no wonder that people wonder whether or not houseplants can think, and whether they might have a consciousness similar to our own. Know that scientists have taken the question quite seriously, but the research and best scientific minds believe plants don’t have consciousness as we think of it. Sure, you can attempt to parse certain aspects of plant perception in ways that parallel human consciousness. In many ways, plants can see, hear, smell, and respond to stimulus, but again the consensus is that the evidence is lacking that plants can learn, feel, or think in complex ways.