Scientific Exploration of Plant Sentience

Alien Earth: What researchers are revealing about the Green Kingdom is reshaping our comprehension of “other” lifeforms

Our accepted understanding of plants is out of touch with scientific research. Historically perceived as passive, sedentary lifeforms, some researchers now recognise plants as active participants in their environments—perceiving, responding, communicating, coordinating and even remembering. 

Research from fields like plant physiology, ecology, and plant neurobiology reveals that plants make complex decisions, sense their surroundings through multiple modalities, and form dynamic social networks that involve both competition and cooperation above and below the ground. Here are just a few snippets of what has been revealed.

Communication and Prediction

In southwest Australia, Verboom and Pate have observed plants native to this region to display asynchronous development between root and shoot systems. It was repeatedly observed that roots expanded in anticipation of water or nutrient needs in advance of those resources actually becoming available. The roots didn’t respond to a resource cue; they anticipated its arrival! Furthermore, communication between shoots and roots is not simply a top-down process. Rather, they found that roots can signal to the canopy to close stomata or alter growth patterns based on below-ground water or nutrient stress. 

Plant Memory and Learning

Monica Gagliano's 2014 study challenged the idea that plants lack capacity for learning and consequentially, memory. Her conclusion, grounded in carefully designed experiments, is yes—plants can not only perceive, but remember, adapt, and change their behaviour in response to experience. All without neurons or a brain. Gagliano's study used the sensitive plant Mimosa pudica, which rapidly closes its leaves when touched. She placed these plants on a shaker table that dropped them a short distance, a harmless but startling mechanical disturbance. Normally, the plant responds to this drop by closing its leaves—a defensive reflex. But over repeated trials, the first unexpected thing happened: the plants stopped closing their leaves. Gagliano interpreted this not as fatigue or damage, but as habituation—a basic form of learning where an organism stops responding to a repeated, non-harmful stimulus. 

Remarkably, when retested 28 days later, the plants still “remembered” that this particular stimulus was not dangerous, and the leaves remained open. 

Even more remarkably, if a novel mechanical disturbance was now introduced—all plants promptly closed up their leaves! 

This kind of long-term behavioural change had never been observed in plants in this way. It has challenged one of biology’s central dogmas: that learning is a function of neurons. 

Plants don’t have brains or nervous systems, but they do have complex signalling networks involving: 

• Electrical impulses (action potentials across cells)
• Hormonal messengers like auxins and jasmonates
• Changes in Gene expression triggered by environmental cues

Gagliano’s findings, alongside similar studies by researchers like František Baluška and Stefano Mancuso, have helped spark a growing interest in plant cognition—a term once seen as fringe, but now increasingly explored in interdisciplinary journals.

Underground Social Networks: Simard’s Mycorrhizal Discoveries

In the coniferous forests of North America, Suzanne Simard’s research on Douglas fir and Birch revealed vast underground mycorrhizal networks. These fungal threads connect tree roots, allowing the exchange of carbon, nutrients, and even chemical distress signals. Her discovery of the so-called "Mother Tree"—older, central trees that redistribute resources to seedlings—revolutionized our understanding of forest ecology. This is not random sharing. It’s selective, strategic, and species-aware resource distribution.

Roots as Environmental and Social Engineers

In Australia’s sandy southwest, Verboom and Pate documented how species like Eucalyptus and Banksia shape their own root environments by forming dense carbonate and clay layers. These layers, it appears, are engineered zones built in cooperation with both fungal mycelia and bacterial colonies where these subsoil organisms synthesise the clay from mineral resources the trees extract from deep groundwater reserves. Payment for services rendered is provided by the trees in the forms of both energy and niche provision for the fungi and bacteria where photosynthetically fixed carbon as complex carbohydrates, amino acids and other organic acids are secreted by roots. This engineered rhizosphere helps regulate water infiltration and retention as well as provides critical nutrient cycling to the Eucalypt and Banksia woodlands. In another study of rhizosphere modification, Pate and Bell investigated particular root structures—cluster roots, found within the Proteaceae plants. These structures exude carboxylates, an organic acid group that has a specific purpose. They mobilise the low levels of phosphorus in ancient, nutrient-depleted soils and they unlock the sometimes highly bound phosphorus in young nutrient rich soils. In both cases, this engineering strategy of the Proteaceae is likely to also benefit the surrounding plant species by making phosphorus more bioavailable as leaf litter and also the overlapping root zone.

Sensory Perception: Seeing, Smelling, Tasting, and Feeling the World

Plants perceive their environment through an array of sophisticated sensory systems. 

They "see" using light-sensitive photoreceptors such as phytochromes, cryptochromes, and phototropins. Early work by Winslow Briggs and Joanne Chory revealed how plants use these receptors to detect light direction, wavelength, duration, quantity and quality, shaping everything from germination to flowering. They use at least four major classes of photoreceptors to achieve this: phytochromes primarily responsible for absorbing the red and far-red wavelengths (600–750 nm), and three types of photoreceptors perceiving the blue to ultraviolet-A region of the spectrum (320–500 nm). Jorge Casal has shown that Arabidopsis seedlings use light to guide their early growth in surprisingly complex ways. Special proteins called photoreceptors help them sense how much light is available, what type it is, and where it’s coming from. For example, in low light, a photoreceptor called PHYA helps the seedling stretch upward, while others like PHYB and the cryptochromes take over once the plant reaches better light, helping it open its leaves and start photosynthesis. Another sensor, PHOT1, lets the plant bend toward light. These light sensors often work together and even interact with each other, helping the seedling make smart choices about how and where to grow. 

Plants can "smell" in the sense that they detect volatile organic compounds (VOCs) released by neighbouring plants. Studies by Consuelo De Moraes (2001) demonstrated that tobacco plants increase production of protective chemicals when exposed to airborne signals from caterpillar-damaged neighbours.

Their ability to "taste"—more accurately, to sense and respond to chemicals—is apparent in root and shoot behaviour. Research has shown that roots and growing tips can differentiate between nitrate and phosphate concentrations and alter their development accordingly. Work by José Dinneny and colleagues has highlighted how roots integrate these nutrient signals to fine-tune their architecture.

Plants sense “touch” via mechanosensitive channels, responding with growth modification—a phenomenon known as thigmomorphogenesis. The word, coined by Mark Jaffe who conducted pioneering work on the phenomenon, derives from three Greek roots, ‘thigma’ for touch, ‘morphe’ for form or shape, and ‘genesis’, for origin or generation. Janet Braam and Wassim Chehab provide an excellent review of the subject in Current Biology. Touch responses are manifested by tendrils, root tips and probably in some cases, leaves. Tendrils use their sense of touch to coil around adjacent structures, enabling vines to climb, root tips also react to touch, such as barriers in the soil which induce changing growth direction. You may have noticed in some forests, a gap between tree canopies, sometimes referred to as crown shyness. Thigmomorphogenesis probably plays some role in this in combination with the trees “seeing” reflected light from their neighbours.

Being upright

Something I never considered beyond seeking light is that most plants know which way is “up”. Yes, plants sense gravity. They do this with intracellular mobile structures called statoliths—dense, starch-filled organelles in root cap and shoot cells that settle to the “bottom” of the cell regardless of orientation of the plant. Studies by Patrick Masson and colleagues helped unravel how this positional sensing guides both root and shoot growth.

Plants as Decision Makers

From Simard’s trees allocating carbon to their kin, to Gagliano’s mimosa “remembering” harmless stimuli, to Australian plants pre-emptively expanding their root systems—one thing becomes clear: decision-making is not unique to animal brains. Studies like those by Elizabeth Van Volkenburgh and Anthony Trewavas propose that plant responses to environmental stimuli are flexible, context-dependent, and reflect a form of biological computation. Plants weigh trade-offs, make adjustments, and change their behaviour accordingly. This reframes cognition as something emergent and not just limited to animal brains.

Final Thoughts

We really do need to review our perceptions of non-animal life-forms. Plants are definitely not passive fixtures in the landscape. We are learning that they are sentient in their own, non-anthropomorphic ways—capable of complex sensory integration, inter-organ communication, environmental engineering, memory, and social cooperation. From the tips of their roots to their highest meristems, plants are active agents in their own survival. 

References

• Blancaflor, Fasano & Masson (1998) – Plant Physiology
• Briggs & Huala (1999) – Annual Review of Cell and Developmental Biology
• Chory (1993) – Trends in Genetics
• Casal, J.J. (2000). "Phytochromes, cryptochromes, phototropin: Photoreceptor interactions in plants." Photochemistry and Photobiology, 71(1), 1–11.
• Casal et al. (1998). "Light quality and the shade avoidance response in plants." Plant Physiology, 118(3), 701–710. https://doi.org/10.1104/pp.118.3.701
• De Moraes et al. (2001) – Nature
• E. Wassim Chehab, Elizabeth Eich, Janet Braam, Thigmomorphogenesis: a complex plant response to mechano-stimulation, Journal of Experimental Botany, Volume 60, Issue 1, January 2009, Pages 43–56, https://doi.org/10.1093/jxb/ern315
• Dinneny et al. (2008) – Science
• Geng et al. (2013) – The Plant Cell
• Gagliano, M., Renton, M., Depczynski, M., & Mancuso, S. (2014). Experience teaches plants to learn faster and forget slower in environments where it matters. Oecologia, 175(1), 63–72.
• Gagliano, M., Vyazovskiy, V.V., Borbély, A.A., Grimonprez, M., & Depczynski, M. (2016). Learning by association in plants. Scientific Reports, 6, 38427.
• Pate, J.S., Verboom, W.H., & Galloway, P.D. (2001). Co-occurrence of Proteaceae, laterite and related oligotrophic soils: Coincidence or causal? Plant and Soil, 233(2), 211–227.
• Lambers, H., Brundrett, M.C., Raven, J.A., & Hopper, S.D. (2010). Plant mineral nutrition in ancient landscapes: High plant species diversity on infertile soils is linked to functional diversity for nutritional strategies. Plant and Soil, 334, 11–31.
• Nishimura, T., Mori, S., Shikata, H., Nakamura, M., Hashiguchi, Y., Abe, Y., Hagihara, T., Yoshikawa, H. Y., Toyota, M., Higaki, T., & Morita, M. T. (2023). Cell polarity linked to gravity sensing is generated by LZY translocation from statoliths to the plasma membrane. Science, 381(6656), 711–716. https://doi.org/10.1126/science.adh9978
• Simard’s Book: Finding the Mother Tree (2021)
• Telewski (1995) – Wind and Trees (Cambridge University Press)