Article by Mike Kluk -
This is Part I of an article that will be published over two months.
Scientists currently estimate that one billion years ago, plants and animals diverged from a common ancestor to form separate kingdoms. Since then, plants and animals have evolved radically different approaches to surviving on earth. There is little wonder then that our “light eating” brethren still have a few surprises for us. This book reveals just what an understatement that is.
Zoe Schlanger is a respected science writer for the Atlantic. The book is carefully researched and well documented with an extensive list of references to peer reviewed journal articles. That is particularly important given its rather remarkable subtitle: “How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth.” The phrase “plant intelligence” is certain to raise a few eyebrows and probably sell a few books. But Schlanger makes it clear from the beginning neither she nor the scientists she interviewed are equating plant “intelligence” with our common concept of animal intelligence. When she does range into more speculative theories or philosophy, she makes it clear she is doing so. On the other hand, new research is revealing that plants are not the passive, noninteractive life forms that they sometimes seem whose only real trick is to turn carbon, hydrogen, and oxygen into sugar. They are quite able to respond to and in some cases manipulate and modify their environment in meaningful ways. They have agency. That seems a better descriptor than intelligence for now given what current science can tell us.
In this article I am going to stick to relaying the quite amazing abilities, as described in The Light Eaters, that some plants exhibit. In many instances, the how and even the why of these are still much debated theories. New observations, new theories new debates and ultimately new understanding of the plant life on our planet is in the not distant future. It is the stuff of cutting-edge science and maybe a sprinkling of philosophy, so stay tuned. For the time being, let’s marvel a bit at what plants can do.
A Chilean shape shifter vine
A common vine in the Chilean rain forest, Boquila trifoliata, has developed a decidedly uncommon ability to imitate the leaves of other plants it is living among. Boquila normally has trifoliate oval leaves but very quickly those leaves can take on the shape, size, color texture and vein pattern of neighboring plants. A single vine has been known to mimic the leaves of four separate plants as it climbs a tree: low growing plants, bushes, taller understory and finally the leaves of the tree. Plant mimicry is not that uncommon over time. Weeds that can begin to look like a food crop are more likely to survive. Both rye and oats started out as scraggly weeds. But as they came to mimic the wheat they were growing among more and more, they became food grains themselves. Boquila is entirely different. It mimics other plants in essentially real time. There is documentation it can impersonate twenty different plants and the list is growing. The adaptive value is pretty clear; if your leaves look like all of the other leaves, your chances of being browsed are less. But the how is unknown. Theories range from the light receptors in its leaves actually being able to detect shape and color (something that is not as far-fetched as it sounds) to the plant being able to somehow incorporate the DNA of neighboring plants into its own or possibly the trick is accomplished with the help of associated colonies of bacteria.
Plant communication can be a long-distance relationship
It has been accepted for some time, that plants, especially trees in a forest, share nutrients through the mycelium network in the soil Taken together, the mycelium are a “mycorrhizal network,” which connects individual plants together to transfer water, nitrogen, carbon, and other minerals. This is a form of communication. Plants need to convey what they are short of and what they have in excess. But that is only the beginning of the extent of communication between plants.
For several years in the mid-seventies, a zoologist, David Rhoades, noticed that a research forest in Washington State was being decimated by an infestation of tent caterpillars. But suddenly the tide changed, and caterpillars began to die. Rhoades, also a biochemist, was able to establish that the trees being attacked had altered the content of their leaves to be less nutritious. It took a few years for the trees to make the switch, but the caterpillars were dying from malnutrition and diarrhea. That was revolutionary for its time; plants were not an entirely passive larvae lunch. But Rhodes noticed something even more unusual. Trees far away from the trees that had been first attacked, far too distant to be communicating through mycelium, had changed the chemistry of their leaves too. They were ready so that when the moths moved on to lay their eggs, the larvae died in the first year. Rhodes hypothesized that the trees were communicating through the air, probably with pheromones.
But Rhoades was not able to consistently replicate his results. Sometimes plants seemed to warn others, sometimes not. The scientific community criticized and even berated him. He was unable to get additional grant funding. He ended his career teaching in a community college.
Later research has confirmed that Rhoades was right. Some of this was done in the controlled environment of the lab. Some in well-designed field experiments. One of the foremost proponents of the idea that plants are not passive and uncommunicative is Rick Karban, a botanist at UC Davis. Even though Karban works in what is, in some respects, the fringes of scientific knowledge, he is a very rigorous and well-respected researcher. His field research, conducted at a UC Davis field station near Mammoth Lakes has demonstrated that sagebrush can communicate with other species, such as wild tobacco using airborne chemicals. That some plants can actually summon predators when being attacked by insects. Not just cross species but cross kingdom communication.
Karban and other researchers have also demonstrated that plants may selectively communicate with only those most closely related. If a threat is mild, they may use a chemical channel that is understood by only their close kin. If broader and more serious, the warning is one that can be understood by a wider range of plants in the neighborhood.
It’s all in the family
The recognition that plants may be able to recognize their close kin and act differently towards them has inspired a whole new course of research. In 2006, a Canadian researcher, Susan Dudley, discovered that at least some plants can recognize who their siblings are. She studied American searocket (Cakile edentula), a beach plant that scatters some of its seeds to the wind but drops others in a bunch. She found that those that had been scattered with other unrelated plants grew roots aggressively, taking over as much of the soil as possible. But when growing in a group of siblings, each plant confined its roots to a smaller area so as not to compete with its siblings. Dudley faced significant skepticism and pushback but persisted. Soon, other researchers began to notice the same phenomena. Researchers in Argentina found that sunflowers grown in groups of close kin produced forty-seven percent more oil than fields of sunflowers from more varied “families.” Close kin groupings would tilt their stalks at alternating angles to avoid shading each other.
Researchers in China found that closely related rice seedlings avoided competition with each other belowground. Their roots were directed to avoid direct competition. But when more distantly related lines are planted next to each other, lateral root length and competition increased dramatically. When the researchers used plastic film to block the potential chemical communication between the roots of closely related kin, family recognition stopped. In other plants however, kin recognition seems to be related to a plant identifying the quality of light reflected off the leaves of kin as opposed to more distantly related plants.
A vampire vine that can select its victims
The dodder vine (Cuscuta spp.) is common in warm moist areas worldwide. Because it lacks chlorophyll, it is dependent on other plants for sustenance. The challenge a dodder sprout faces is clear; it must find a host to sink its spikes into soon or perish. Time lapse photography shows the tip of the emerging seedling moving in a circle. Is it, in fact, sampling the “emanations” of neighboring plants, trying to detect a suitable host. It cannot effectively parasitize all plants, grasses for example. So, when experimentally grown between a stalk of wheat and a tomato plant, after a couple of circles, the seedling will consistently grow towards the tomato and ultimately parasitize it. When sprouting among a group of potentially suitable hosts, dodders can detect and choose from a distance those that were grown in nutrient rich soil as opposed to nutrient poor soil. And when given the choice between two potentially suitable hosts that are different distances away, the closer of the two is selected. It appears dodder seedlings can also use the light passing through neighboring plants as a clue to locate desirable hosts. When faced with a light array designed to look like a grass and one designed to look like a branching plant, they inevitably chose the latter.
This article will be continued next month. So, if you found this part interesting, be sure to look for the rest in July.
Editor’s note: In case you missed it, Mike Kluk also wrote Interview with a Plant Whisperer – UCD’s Dr. Richard Karban in May 2025.