A Blog by

Can a Plant Remember? This One Seems to—Here’s the Evidence

There’s this plant I’ve heard about that had a really bad afternoon a few years ago. It was in its pot bothering nobody and then, suddenly, it fell. Not once, but 56 times. (I’ll explain in a minute.) But it’s a plant. Things happen to plants, and as far as I know, they go on as before. They don’t have brains. They have no way to “remember” anything. They’re not animals. So I figure even 56 consecutive falls left no lasting impression.

I figured wrong. I just read an eye-popping paper by Monica Gagliano, associate professor of biology at the University of Western Australia. She’s got a plant that not only “remembered” what happened to it but stored that memory for almost a month. She saw this happen! Here’s the plant:

Picture of mimosa pudica leaves folding in after they are touched
Sensitive plant, shame plant (Mimosa pudica), flower and leaf, leaves sensitiv, leaflets folded after touching
Photograph by blickwinkel, Alamy

Gardeners call Mimosa pudica “the sensitive plant,” because if you touch it even lightly or drop it or disturb it, within seconds it folds its teeny leaves into what looks like a frightened or defensive curl. It’s fun to watch it get all shy (two and a half million people have seen this pokey, pokey video. You don’t have to watch it all, but it’ll get you in the mood.)

OK, so it’s highly sensitive. Knowing this, here’s what Gagliano did: She got a bunch of Mimosa pudicas, put them in pots, then loaded each one onto a special plant-dropping device using a sliding steel rail that worked like this:

Drawing by Robert Krulwich
Drawing by Robert Krulwich

Each potted plant was dropped roughly six inches, not once, but 60 times in a row at five-second intervals. The plants would glide into a soft, cushiony foam that prevented bouncing. The drop was sufficiently speedy to alarm the plant and cause its teeny leaves to fold into a defensive curl.

To “Eeek!” or Not to “Eeek!”

Six inches, however, is too short a distance to do harm, so what Gagliano wondered was: If she dropped 56 plants 60 times each, would these plants eventually realize nothing terrible was going to happen? Would any of them stop curling?

Or, to put it another way: Could a plant use memory to change its behavior?

To find out, she kept going with her experiment. And, as she writes in her paper, fairly quickly “observed that some individuals did not close their leaves fully when dropped.” In other words, plants seemed to figure out that falling this way wasn’t going to hurt, so more and more of them stopped protecting themselves—until, as she later told a room full of scientists, “By the end, they were completely open … They couldn’t care less anymore.”

Drawing by Robert Krulwich
Drawing by Robert Krulwich

Is this evidence of remembering, or is it something else? Maybe, skeptics suggested, all we’re seeing is a bunch of exhausted plants. Curling is work. It takes energy. After 60 drops, these plants may simply be pooped out—that’s why they don’t trigger their defenses. But Gagliano, anticipating this question, took some of those “tired” plants, put them in a shaker, shook them, and instantly they curled up again. “Oh, this is something new,” she imagined them saying, something that hasn’t happened before. That sense of a “before,” she said, is the best explanation for the plants’ change in behavior. They didn’t curl up again because “before” they’d learned there was no need. And they remembered.

A week later—after the shakings—she resumed her drops, and still the plants failed to get alarmed. Their leaves stayed open. She did it again, week after week, and after 28 days, these plants still “remembered” what they’d learned. That’s a long time to store a memory. Bees, she noted, forget what they’ve discovered in a couple of days.

But Without a Brain, How Do They Do It?

“Plants may lack brains,” Gagliano says in her paper, “but they do possess a sophisticated … signaling network.” Could there be some chemical or hormonal “unifying mechanism” that supports memory in plants? It wouldn’t be like an animal brain. It would be radically different, a distributed intelligence, organized in some way we don’t yet understand. But Gagliano thinks Mimosa pudica is challenging us to find out.

Michael Pollan, writing in the New Yorker, hung out with Gagliano last year, went with her to a science meeting, and vividly describes how she was roundly dismissed by many biologists, who bridle at the idea that any plant could be “intelligent.” Plants, they insist, are mainly genetic robots—they can’t learn from experience or change behavior. To say they can “generates strong feelings,” Pollan writes, “perhaps because it smudges the sharp line separating the animal kingdom from the plant kingdom.”

Drawing by Robert Krulwich
Drawing by Robert Krulwich

Plants have always been the bronze medalists, one step down from the animals, two steps down from us, the golden ones. By giving plants animal-like talents, Gagliano is mucking up the hierarchies, challenging the order of things.

We like to think because we have such big brains, we’re exceptional. Our trillions of neurons are keys to memory, feelings, consciousness. Brainless creatures by definition can’t do what we do—so of course, plants can’t “remember.”

But Gagliano says maybe they can.

“What we have shown here,” she says at the end of her paper “leads to one clear, albeit quite different, conclusion: the process of remembering may not require the conventional neural networks and pathways of animals; brains and neurons are just one possible, undeniably sophisticated, solution, but they may not be a necessary requirement for learning.”

And who knows? Maybe she just found the plant that will one day prove her right.

Editor’s Note: This post was originally published with a photo of a plant that was misidentified as Mimosa Pudica. We have since updated the post with a new image.

30 thoughts on “Can a Plant Remember? This One Seems to—Here’s the Evidence

  1. A being that can signal can store information, including not only plants but microorganisms. I don’t know why this is being disputed.

    1. A seed has memory. . I also have this plant growing and it does have intelligence in every part of it..if you touch the leaves it closes but if the stem is also touched it folds back..like a arm..it also has medicanal properties in it..

  2. Although not mentioned in this article, it seems that she may be on to discovering the evolutionary precursors to the chemicals signals that we use for memory.

    1. You reminded me of an old Hitchcock story I read as a kid. In the end, the tree branch fell on him and feasted on his blood. As an aside, oak trees will assassinate other trees it doesn’t want by sending out chemicals, others will feed others nutrients they need. Apparently that one works in combination with mushrooms. And in the Botany of Desire one guy was doing a study in which bacteria were dropped into boiling water in a separate room. When they fell, the plant (which was having it’s electrical energy measured) let out an equivalent of a scream. It seems to me the idea of intelligence is too narrowly defined. And that given what we’ve done with our intelligence, it may be over-rated as well. So beware the tree! 🙂

  3. The picture of the plant on top of the page does not seem to be Mimosa pudica more commonly know in the states among educators as a TickeMe Plant. Mimosa pudica has pink flowers. I grow TickleMe Plants with my students and have observed them “remembering” that the bouncy ride in my car was no reason to close as they “learned” and did not close after a while traveling in my car. Also I had them stop closing with a constant fan blowing on them.

    1. Hi Samantha,

      I’m Becky, one of the producers of this blog. Thanks for pointing out your doubts about the veracity of the caption of the Mimosa pudica plant. Getty is currently working with its researchers to confirm the exact species of the plant. I’ll update the post with that information as soon as possible.

      Becky

      1. Definitely not Mimosa pudica in this photo. Appears to be Acacia dealbata, sometimes called “mimosa” as a common name. Same family of plants, but certainly not the sensitive plant, Mimosa pudica, which has pink flowers and a creeping habit.

    2. Thanks again for pointing out that the plant in the photo was misidentified as Mimosa pudica. We have updated the post with an accurate image an an editor’s note.

  4. I think this article would have been much more interesting if the author had reported what are the points other scientist do not agree with. Were there methodological errors?

  5. Perhaps the act of leaf closing requires a certain amount of a chemical that the plant very slowly manufactures. The first touch of the leaf triggers a reaction from the “full tank” of the chemical and spurs the plant into making more of this chemical. BUT it takes time to make this chemical, so retouching the leaf during this period calls upon a dilute solution of this chemical while the plant is striving to bring it back up to full strength. Doing it a number of times reduces the power of this chemical until it can be fully replaced by the plant. It would be the same as driving a sap collector into a maple tree and then driving ten of them into the tree and observing that the tree no longer wants to give the same volume of sap per collector.

    1. If that were the case, then leaf folding response to the different stimulus of shaking post “habituation” to the dropping would not occur.

    2. Have done a similar experiment by blowing on the plant with a fan with similar results. At the end of the test when i heated the tip of the leaves they curled up. I did this at home and not under controlled conditions. I liked your theory and tested it for myself.

  6. StarryGordon is right: All living things sense their environment and subsequently respond—the time delay implying some memory. Bacteria also have an adaptive immune mechanism that protects them against viruses (called CRISPR/Cas), a type of memory system that is now being used for genetic engineering. Plants have hormone-like signalling systems called auxins. When they grow during the night toward light detected during the day, it seems that they “remember”.
    Everything long considered unique to humans—memory, emotions, cooperativity, consciousness, etc—has counterparts in all living things. Wouldn’t it seem fair to conclude that Mimosas have a fear response to touch? That they become “conscious” of being in a threatening or nonthreatening environment?

  7. The leaves close by means of hydathodes – water filled cells that release water.
    The memory she describes is most likely merely a reduction in physical sensitivity to that particular stressor. She changed the stressor (by shaking) and the hydathodes closed the leaflets.
    She repeated the “learned response stressor” – the 6″ drop – but the tissues were still altered to not react to that particular stressor.

  8. well I think It’s just because the plant couldn’t do it anymore, the system of closing the leaves is not forever-working and there’s a limit of times the plant can close the leave 🙂

  9. I occasionally set my Mimosa plants outdoors where they are exposed to random breezes. Usually within a couple of hours, they habituate to the wind and the leaves remain open. Apparently some selective chemical mechanism acts as a switch to turn off the closing response to specific stimuli because even after they “learn” not to react to the wind, the leaves still respond by folding to touch and bumping under those conditions.

  10. Maybe when the plants are dropped repeatedly because of continuous irritation by the same stimulus the signal transduction pathway is somehow disturbed or upset which fail the plants to perceive or fully perceive the same stimulus again & they don’t produce any response. And when a time break is given they can regain this ability ( or otherwise loose the memory ). But when the plants are shaken in a shaker may be they perceive it as different stimulus and use alternative pathway to produce response.

  11. The show Beyond Belief: Fact or Fiction (SEASON 4 EPISODE 8) featured a story about homicide detectives catching the man who murdered a florist by hooking a red Amaryllis, which was present during the murder, to a lie detector and performing a criminal line up looking for responses in the flower to each suspect. The show purports the story is true and happened in New York City in the late 1970s. They cite research by author/novelist Robert Tralins.
    (SOURCE: Wikipedia)

    1. Michael — this is such a kick in the head! It seems pretty close to totally improbable, that a plant would identify an individual human, even a murdering one. I’ve been reading lately about animals that recognize human individuals; angler fish seem to, crows do, I’ve read accounts of bees picking out the same individual over a series of days, but a plant fingering (oops, they don’t have any) a felon– that’s pretty wild.

  12. The article provides an empirical reason to believe that plants may ‘learn,’ but so little evidence is offered that it is difficult to characterize the process unequivocally. It raises more questions than it answers.

    If you water a plant less frequently but soak it more thoroughly each time, the plant will ‘learn’ to extract water from deeper levels in the soil; that is, the plant will grow longer roots. Likewise, if a plant does learn from its daily experiences, as the article suggests, that learning must be accompanied by some physiological change in the plant, just as its roots grow longer when water can be found a few inches away. We know that human learning is accompanied by changes in the size and relationships between neurons in the human brain. What is the physiological marker of learning in this case?

  13. Has anyone been looking at this from a sub atomic level? How everything is connected….so therefore memory is included in the new cells and are recording everything.going on. It does not matter if human animals plants whatever it is. Also VIBRATIONS play a key role. In the universe/ multiverse …..The empty space called dark space…(many names) has been recorded by scientist to have similar to our brain synaptic endless connections to vibrations, magnetic fields…..In short everything is alive, has memory, and is created to give us endless fun to explore the possibilities of what may, is, or can be so. Check out “Gregg Braden” highly intelligent scientist who has studied metaphysics,and is always researching. LOVE JOY AND PEACE TO ALL.

  14. What is memory? Is it stored information? If so, then every seed and every cell is capable of memory.
    If it is stored information of environmental events, then perhaps tree rings are a form of memory.
    Do we know if human memory is chemical, electrical or something more mysterious.
    I have plants that close their flowers at a certain time every day, others that will not open until the sun shines. Is this memory?
    Many plants respond to daylight length. This can be manipulated by light control. Many animal responses can also be manipulated. Think of Pavlov and his conditioned reflexes in dogs. Does the dog remember that he is about to be fed when the bell rings.
    If we define memory as “stored information” then of course plants can remember.

  15. It appears this research, and some of the comments, are getting away from actual science and more into pseudoscience. The person doing the experiments seems to have her mind already made-up on whether or not the plants actually have memory. All plant movement is most likely based on passive mechanical and chemical reactions, not sensory response.

  16. I had heard 2 streams from childhood.. one which says plants respond and then the science which says whatever you think insider is irrelevant and they cant understand that. I always inclined towards the side of science since they are more factual and proof driven.

    Then a week back, my family and I were at a place. I saw ‘touch me not plant’.. we all touched – it closed. We were super excited (as I used to be in childhood on touching this plant).
    I somehow decided to stop and let others go ahead. I prayed to plant (all inside my mind) – to let me know if it can indeed understand what I feel. I said, I am not going to hurt it and that if it understands this – it need not close the leaves. I touched them. They DID NOT CLOSE this time. I was so shocked.. I just kept touching my forehead. I called my mom. I told her this entire thing. Along came my niece. My mom did the same thing – touched it – it didn’t shy. my niece who is very young – touched it – it curled the leaves. I again did once it was normal – it did not close.
    Next time, when I was touching again – my hubby called and said its too late.. i lost my concentration – again touched it. IT closed 2 leafs by the time i could get back my concentration and STOPPED!
    I was shaking with disbelief and joy of finding out that its true!

    Does anyone have any explanation that is not too meek?

    1. I remember watching this bad documentary once that was far too “new-agey” for me. However, they had a segment in which this Buddhist monk would meditate over these jars of water. He would meditate with specific emotions (a very difficult task, I can say as I have been meditating since 1976 and find this difficult even now!). They then photographed the water molecules with a microscope and each emotion created a different pattern in the water. Science is also not nearly as factual as you imagine. What is researched often depends upon the profits that can be generated from the results. In other words, much of our research is profit driven, while real science is barely funded. There was a quote by Einstein which I don’t really remember well. It went went something like, “Science is ignorance based upon prejudice” It is a horrible paraphrase, but it gets to the pith of it. Science should always question its’ own beliefs, but it rarely does. There is no money in it. There are scientists today who question whether or not humans are actually conscious beings. I believe Hawkings is one of them. While the vast majority of people may not be truly conscious, it is a false and shallow argument. Yet, because of his stature, he is not truly questioned. Mystics knew of this thousands of years ago. True science is based upon observation of all factors. Modern science is not that inspiring to me. It sold its soul long ago.Always question authority of all kinds. Sorry for the rant.

Leave a Reply

Your email address will not be published. Required fields are marked *