Plants, we are learning, have internal means of remembering and keeping track of things:
In a study published in Nature Communications, researchers from Nara Institute of Science and Technology have revealed that a family of proteins that control small heat shock genes enables plants to ‘remember’ how to deal with heat stress…
“Heat stress is often repeating and changing,” says lead author of the study Nobutoshi Yamaguchi. “Once plants have undergone mild heat stress, they become tolerant and can adapt to further heat stress. This is referred to as heat stress ‘memory’ and has been reported to be correlated to epigenetic modifications.” Epigenetic modifications are inheritable changes in the way genes are expressed, and do not involve changes in the underlying DNA sequences.Nara Institute of Science and Technology, “How to beat the heat: Memory mechanism allows plants to adapt to heat stress” at ScienceDaily (June 10, 2021) The paper is open access.
Of course, plants don’t have ideas, as such. What they may remember (have an internal record of) is physical things that happened to them. Epigenetics (the genetic changes that are not inherited but acquired from a life form’s experience and then passed on) may function as a sort of memory in the absence of a brain or mind.
Plants have other ways of remembering things that researchers have begun to learn about over the last decade or two. In some cases, they can transmit information through special cells:
As reported by the BBC July 14, scientists found that light shining on a leaf cell triggered a cascade of events that was immediately signaled to the rest of the plant via a type of cell called a bundle sheath cell. Those cells exist in every part of a plant. Karpinski, of the Warsaw University of Life Sciences in Poland, measured the electrical signals from those cells, and compared it to finding a central nervous system for plants…Rebecca Boyle, “Can Plants Think?” at Popular Science (July 15, 2010)
Some plants can remember things for up to a month:
Abstract: In Mimosa pudica-the sensitive plant-the defensive leaf-folding behaviour in response to repeated physical disturbance exhibits clear habituation, suggesting some elementary form of learning. Applying the theory and the analytical methods usually employed in animal learning research, we show that leaf-folding habituation is more pronounced and persistent for plants growing in energetically costly environments. Astonishingly, Mimosa can display the learned response even when left undisturbed in a more favourable environment for a month. This relatively long-lasting learned behavioural change as a result of previous experience matches the persistence of habituation effects observed in many animals. © 2014 Springer-Verlag Berlin Heidelberg.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.
“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.Robert Krulwich, “Can a Plant Remember? This One Seems to—Here’s the Evidence” at National Geographic (December 14, 2015)
Doubtless, there is, in each case, a chemical system by which the plant keeps track and we are slowly beginning to document such systems in a variety of plants. Think of the plant’s signaling system, perhaps, as an internal counter rather than a brain or a mind.
If so, the counting system could cause processes to kick in or not, depending on the chemical environment:
Of the possible plant talents that have gone under-recognized, memory is one of the most intriguing. Some plants live their whole lives in one season, while others grow for hundreds of years. Either way, it has not been obvious to us that any of them hold on to past events in ways that change how they react to new challenges. But biologists have shown that certain plants in certain situations can store information about their experiences and use that information to guide how they grow, develop, or behave. Functionally, at least, they appear to be creating memories. How, when, and why they form these memories might help scientists train plants to face the challenges—poor soil, drought, extreme heat—that are happening with increasing frequency and intensity. But first they have to understand: What does a plant remember? What is better to forget?Sarah Laskow, “The Hidden Memories of Plants” at Atlas Obscura (September 5, 2017)
In one sense, we always knew that plants could remember. They know, for example, if they have been through a winter in order to begin germination in the spring. But we didn’t know how they were doing it or how much they can really “remember” (due to internal chemical changes).
So plants don’t have minds or brains but that doesn’t turn out to be essential for just keeping track of things.
You may also wish to read:
Researchers: Yes, plants have nervous systems too. Not only that but, like mammals, they use glutamate to speed transmission (April 11, 2019)