Plants are Plants: Personal Reflections from a Plant Physiologist

Plants are plants.

The statement seems obvious. Yet over the course of my life as a plant physiologist, I have come to regard it less as a truism than as an invitation to look closer. We say “plants are plants” as if we know what that means. But in fact, we do not. Many aspects of plant physiology and behavior remain unexplained. Much of my scientific career has been devoted to understanding what it means to be a plant, and the process by which we gain that knowledge.

The humans who observe, study, and live alongside plants often find themselves identifying with them. We attribute to plants human or animal characteristics, perhaps o make them more familiar. Yet this tendency can miss the point. Plants are not animals. They have evolved in fundamentally different ways, not least in that they make their own food, producing the energy on which nearly all life depends. If plants are difficult for humans to understand, it is not because they are simple, but because they are plants.

Because the more closely we study plants, the more our assumptions can falter. While many plant adaptations are now described as “intelligent behavior,” the nature of plant intelligence remains difficult to characterize. As scientists search for the biological bases of knowing, remembering, deciding, and acting in plants, we are repeatedly confronted with the limits of our own frameworks. The difficulty, I have come to believe, lies not only in plants themselves, but in the ways we have learned to do science.

What follows is a personal meditation on some key lessons I have learned over twenty-five years as a scientist hoping to understand, and teach about plants as plants.

My research career has revolved around what appears to be a simple question: How do leaves grow? As a plant physiologist, I focused on the cellular and physiological processes that regulate growth rate. What mechanisms cause leaves to grow faster or slower? Most people assume we already know the answer. In fact, when I told friends and family about my work, they laughed and said, “Don’t we already know that?” Growth, they assumed—as many scientists did at the time—was simply the result of photosynthesis.

But that explanation never fully satisfied me. I began this work as a technician at Duke University’s Phytotron after earning a BS in Botany. There, I worked under Paul Kramer, a leader in the study of how plants gather, retain and lose water, and deal with water deficit and water stress. His research team handed me a ruler and assigned a simple task: measure daily the length and width of cotton and soybean leaves in the field, greenhouse, and growth chambers.

What surprised me (and surprises nearly everyone who does this) is how quickly leaves grow. Within just a few hours, measurable change occurs, visible to the naked eye. This simple act of watching growth unfold in real time is often what first convinces people that plants are living beings. They move. They change. And we can see it.

Yet that realization raised deeper questions. If growth is so dynamic, so responsive, then what precisely governs it?

I continued to explore this question as a graduate student in the laboratory of Robert Cleland at the University of Washington. Cleland’s group was developing what became known as the Acid Growth Theory, which remains the best available explanation for how plant hormones regulate cell elongation. The prevailing view held that light stimulates leaf growth through photosynthesis: Light produces sugars, sugars fuel growth.

But our experiments showed otherwise. Albino leaves, incapable of photosynthesis, grow just fine.¹ Toxins that block photosynthesis do not block growth. Clearly, light was acting through another process. But how? 

To investigate, we turned to increasingly sophisticated instruments: position transducers to measure growth rates continuously, electrodes to track ion fluxes, tools to measure pH changes at the leaf surface. We discovered that red- and blue-light photoreceptors regulate ion movement and cell wall acidification, which in turn control growth rate.² We had identified signals that switch growth on and off and learned something about how those switches work.

These fundamental findings had important practical implications. For example, plant breeders could use growth rate to predict yield and biomass production. Subsequent collaborative research showed that leaf growth rate proved to be a strong predictor of productivity in poplar plantations and bean crops … until it didn’t.³ When plant canopies closed and plants sensed their neighbors via phytochrome signaling, growth slowed in leaves and accelerated in reproductive organs. We found that, in older plants, leaf growth rate was inversely related to yield! In other words, we had found just the opposite of what we’d predicted, contradicting ourselves but, in the process, making our work that much more useful. This finding expanded our work to look at the whole plant and ask: How do plants know to shift growth from one organ (e.g. a leaf) to another (e.g. a pod)?⁴ This is a good example of how the simplest of questions, how do leaves grow, can lead to more complicated ones, laying a foundation for understanding adaptive behaviors in plants.

Here was the lesson science taught me again and again: even our most elegant explanations remain provisional. Sometimes the simplest questions lead not to simple answers, but more questions. Plant growth, far from being a straightforward outcome of photosynthesis, revealed itself as an integrated, adaptive process: one that coordinates perception, signaling, and response across the entire plant.

As my career progressed and I earned tenure, I felt freer to ask broader questions. Growth underlies much of what we describe as plant behavior. But what, exactly, counts as behavior? And what counts as knowing?

These questions followed me into the classroom. I developed a course called The Physiological Basis of Plant Behavior, hoping to attract University of Washington biology students to learn about plants. In the class, I asked students to solve puzzles that required them to explain plant actions using physiological mechanisms. For example, corn seedlings planted in rows orient their leaves perpendicular to the rows, so they don’t self-shade. How do they know where to put their new leaves? Another puzzle: Plants respond to the buzzing sound caused by chewing insects by synthesizing proteins to make their tissues undigestible. By what mechanism do they detect the sounds, and how is this information conveyed to the machinery that makes the toxins?

One year, an anthropologist studying plant neurobiology, Kristi Onzic, joined my class as part of her fieldwork. She noticed that students had intuitively self-sorted at tables according to shared backgrounds: local students sitting with local students, international and transfer students gravitating toward one another. (I should note, academic performance was similar across these groups). Curious about how these lived affiliations might shape students’ relationships to science, Kristi conducted an informal experiment. She asked each group to draw a circle representing all they knew about the world, and within it a second circle indicating how much of that knowledge they believed came from science. The results were striking. Students who had grown up locally and entered the university directly drew circles that nearly overlapped: For them, scientific knowledge constituted most of what they knew. Students from other countries or educational pathways drew much smaller inner circles. Science, they explained, was important, but it was just one way of knowing among many.

This exercise reinforced a question I often return to in my conversations with others about plants: What is science, and what is it not? How does science contribute to what we know? Many take science as a monolithic entity that produces singular truths that explain reality. And while science excels at testing hypotheses and generating reproducible data, its hypotheses often arise from individual imagination, intuition, and lived experience. Hypotheses are speculative explanations of reality; alone they are not science but rather dreams of reality. Scientific methods challenge the dreams and contribute evidence for how things work in a physical and chemical world. 

The question of science’s proper scope arises sharply in debates over plant neurobiology, a debate I know well. In 2005, when the Society for Plant Neurobiology was founded, I was asked to serve as chair of its Organizing Committee, and later became President. The Society brought together scientists investigating how plants perceive, integrate, and respond to their environments, work that challenged long-standing assumptions about what plants can do and how we should describe it. 

The term plant neurobiology was chosen deliberately. It was meant to provoke conversation about integration, signaling, and coordination in organisms without nervous systems. And almost immediately, questions erupted across the plant biology community. Was “neurobiology” an accurate or misleading term when applied to plants? Was there any scientific evidence that plants were in any meaningful sense “neural”? Could plant signaling networks be legitimately compared to animal nervous systems? These questions animated early symposia of the Society and generated a wave of editorials and responses in the literature. For well-considered reasons, the group changed its name in 2009 to the Society for Plant Signaling and Behavior. The research continued, as did the journal, under that name.

The term itself was intentionally provocative. Critics responded forcefully. Plants, they argued, possess no neurons, no brains, and therefore no consciousness; to suggest otherwise was to mislead students and open the door to pseudoscience.

To bring these questions into the classroom, I asked my students to read a series of papers by Lincoln Taiz and colleagues, including the strongly worded essay “Plants Neither Possess nor Require Consciousness.”⁵ In this paper, Taiz et al. argue that consciousness depends on a threshold level of neural complexity found only in animals with brains, and that claims about plant intelligence rely on misleading metaphors rather than empirical evidence. They emphasize that many plant behaviors (e.g., electrical signaling, rapid movements, growth responses) can be explained through known physiological mechanisms, without invoking cognition, intention, or subjective experience. They also warn that framing plant biology in cognitive or neurobiological terms risks confusing students about what constitutes legitimate scientific explanation.

These arguments sparked intense discussion.⁶ My students agreed that claims about plant consciousness require extraordinary evidence. At the same time, they were troubled by the implication that physiology alone is sufficient to explain all aspects of plant behavior, and that integrative frameworks analogous to neurobiology are unnecessary or even illegitimate. They rejected the suggestion that they were being misled. On the contrary, they felt energized and curious.

In response, the students decided to write their own paper, later published as “Understanding Plant Behavior: A Student Perspective.”⁷ Rather than arguing that plants are conscious, they focused on how scientific inquiry proceeds. Hypotheses, they noted, arise from diverse experiences, imaginations, and cultural backgrounds; testing and refinement follow. Framing plant function as behavior (rather than as a collection of isolated mechanisms) invited a broader range of questions and drew more students into serious engagement with physiology itself. As they wrote, “Scientific progress often requires challenging the boundaries of disciplinary languages, techniques, and trainings,” asking what cultural assumptions might be standing in the way of discovering new plant behaviors.⁸

For me, this exchange crystallized what was at stake in the plant neurobiology debate. The controversy was not simply about terminology, but about how science defines its own limits. Plant neurobiology, for all its tensions, revealed something essential: Scientific progress often occurs at the edges and boundaries of language, where concepts strain to keep pace with phenomena.

This debate casts a long historical shadow. Back when I was working at the Phytotron, I had plenty of time between my measurements to explore the research building. One day, I discovered a copy of the cult classic 1973 book, The Secret Life of Plants, hidden beneath a sink.⁹ The book captivated me, even as I recognized aspects lacked rigor. Its popular success, however, had real consequences. Many people shunned research into plant behavior. Shortly after publication of the book, federal research funding for plant electrophysiology dried up, stalling the field for at least 25 years. 

One figure in that book deserves special attention: Jagadish Chandra Bose. An engineer trained in England, Bose developed extraordinarily sensitive instruments to measure plant growth and electrical signaling in the early twentieth century. His experiments demonstrated plant movement, perception, and responsiveness with remarkable precision. Yet his work was largely excluded from mainstream science: partly because he worked in colonial India, partly because he was a mystic and a poet, and partly because his findings unsettled established categories.¹⁰

It took nearly a century for Bose’s work to be taken seriously again. His story serves as a cautionary tale: Science does not simply discover truth; it also decides what counts as discoverable. In other words, plants are plants, but who gets to say so, and how, is more than simply a scientific question. 

Many fear that research into plant behavior will once again drift toward pseudoscience. Popular enthusiasm can blur distinctions between hypothesis and evidence. That concern is not unfounded. Scientific rigor matters, and physiology remains indispensable to understanding how plants function. 

Where critics and I disagree is not over what plants are, but over how science should respond to what it does not yet understand. To insist that current physiological explanations are sufficient is to risk foreclosing questions before they can fully take shape. To restrict inquiry to existing disciplinary languages is to assume, prematurely, that those languages are already adequate to the phenomena before us. We can test bold hypotheses carefully, allowing concepts to evolve, while remaining attentive to signals that do not yet fit established frameworks.

Plants are plants. But taking that statement seriously requires more, not less, curiosity. If plants continue to surprise us, it is not because we have been careless in studying them, but because they insist on being understood on their own terms. And learning what those terms are remains an unfinished scientific task.