10 Mysteries of Plant Intelligence

Plant intelligence? It sounds like an oxymoron. Because plants lack a central nervous system, we tend to see them as simple. However, flora have shown the ability to count, learn, communicate, adapt to environmental cues, perform arithmetic, camouflage by mimicking neighbors, form vast fungal networks, and even show memory. Not only do plants challenge our biases about intelligence, but they may also serve as models for future medical breakthroughs, industrial technologies, and space exploration.

Related: 10 Ways Plants Try to Defend Themselves from Being Eaten

10 Plant Arithmetic

The Venus flytrap counts. Up to five, in fact. Touch two hairs within a 20-second window, and the trap shuts. Touch five, digestion begins.

Dionaea muscipula became carnivorous to cope with poor soils. Flies and ants offer an attractive meal, but catching and breaking them down is calorically expensive. The plant counts in order to save energy. It needed to figure out how to tell the difference between a non-prey stimulus—like raindrops or debris—and a morsel worthy of jasmonic acid synthesis.

Bright colors and sweet nectar attract prey to the inner surface of the trapping leaves. Each touch develops an action potential with a calcium wave. If a second wave emerges before the action potential returns to baseline, the trap shuts within one-tenth of a second, entombing the fast-moving prey. Researchers refer to this biological clock as a form of short-term memory.

Some mutant flytraps are born without the ability to count. Researchers have found that applying exogenous jasmonic acid, the plant hormone that triggers digestive pathways, can restore the digestive response.^[1]

9 Chemical Communication

Leaf beetle larvae relish goldenrod, but goldenrod has something to say about it. When these critters beset the plant, Solidago altissima releases chemicals carrying a message: the plant is damaged and a bad food source. Undamaged goldenrod picks up the chemical signal and launches a preemptive defense against the larvae.

Goldenrod can tolerate losing 30% of its leaf mass to insects. Any more is deadly. So, this system is designed to keep larvae moving. As a result, the damage spreads across the entire population of plants rather than concentrating on one individual.

Researchers have observed chemical communication in 35 plant species. These volatile organic compounds (VOCs) are used not only to deter herbivores but also to attract predatory insects and can signal other plants—even completely unrelated species—to initiate defense responses. Because goldenrod grows in densities similar to crops, researchers are exploring ways to harness the power of VOCs in agriculture.^[2]

8 Wood-Wide Web

In 1997, Suzanne Simard found something shocking under the soil of British Columbia forests: vast webs of fungi connecting the roots of trees. These common mycorrhizal networks (CMN) became known as the wood-wide web because they resembled the internet. Simard observed carbon exchange between paper birch and Douglas-fir. She also observed that insect-plagued Douglas-fir communicated with nearby ponderosa pine, which in turn began producing defensive enzymes against the six-legged threat. Plants provide the fungi with carbon fixed from photosynthesis. In turn, fungi provide the plant with nitrogen and phosphorus. However, the same symbiotic networks can sometimes become parasitic.

Some of Simard’s broader claims have come under scrutiny. Evidence remains limited on how widespread CMNs are, their positive impact on seedling success, or whether mature trees use them to direct resources to their offspring.

Here’s what we know: CMNs exist and connect the roots of trees with other trees, shrubs, seedlings, and herbs. These networks transfer nutrients, carbon, water, and infochemical signals. What’s more, the discovery of CMNs has changed the way scientists see a forest—not as a series of independent, isolated trees, but as interconnected networks.^[3]

7 Thermogenesis

Warm-blooded plants? Sounds like science fiction. However, some plants like skunk cabbage are thermogenic—they make heat metabolically.

Symplocarpus foetidus often blooms before snowmelt. This member of the arum family generates heat by cyanide-resistant cellular respiration in its mitochondria. An abundance of these cellular powerhouses causes the spadix at the flower’s center to be about 20°F (-6.7°C) warmer than the surrounding air. It can accomplish this feat for over 14 days, providing an ideal early spring pollination and flower maturation.

The flower’s name derives from its fetid smell. This funk lures pollinators like gnats and flies, which most likely mistake the smell for carrion. Lotus and common pawpaw are also capable of producing metabolic heat. Curiously, they specialize in attracting beetles, as they evolved before bees became the prime pollinator.

Thermogenic plants’ ability to recognize and adapt to their environment has led some to refer to them as intelligent. In November 2005, researchers from the University of Morioka discovered skunk cabbage were using up to three variables to regulate their internal temperature—not unlike an oven thermostat. In Japan, the plant is known as the “Zen plant” for its perceived resemblance to a monk in meditation.^[4]

6 Boquila Vine Mimicry

The Boquila vine is a chameleon. This Chilean rainforest creeper mimics the leaves of plants it uses for support, and occasionally even nearby specimens it has no contact with. Boquila trifoliolata was first described in the 1800s, but it wasn’t until 2013 that its mimicry was revealed. Plant ecologist Ernesto Gianoli realized that an unknown specimen was a Boquila vine imitating one of its host plant’s leaves. After this discovery, Gianoli found Boquila mimicking more than 20 species of plants.

No one knows how Boquila shape-shifts. Some suggest chemical exchange. Others point to genetic transfers from the host to the chameleon creeper. In 2021, Gianoli published a paper pointing to microbiome similarities between model and mimic, suggesting that bacteria might have a role.

Boquila uses mimicry to avoid herbivory. First, it climbs above ground-based grazers. Then it confuses visually based herbivores by hiding its succulent vines amongst less palatable species. Curiously, a single Boquila vine associated with two separate species can mimic both.^[5]

5 Root Hearing

For decades, people have suggested that plants can hear music—that they even have genre preferences. While this is mostly considered pseudoscience, recent research has provided evidence that plants can detect certain sounds.

In 2016, Monica Gagliano of the University of Western Australia found that pea plant roots can hear water. Pea seedlings grown in mazes were forced to make directional decisions. Their roots grew toward the sound of water—even if it was contained within a pipe that was not easily accessible. However, Pisum sativum did not grow toward recordings of running water, and white noise repelled them. When given the choice between the sound of water within a pipe and moist soil, the seedlings opted for the moist soil. Peas seem to use sound when sourcing water at a distance, but moisture gradients when nearby.

How plants hear remains a mystery. Michael Schöner of the University of Greifswald believes that “sound vibrations could trigger a response of the plant via mechanoreceptors—these could be very fine, hairy structures, anything that could work like a membrane.” Findings like these remain debated and require replication, but they hint at surprising plant sensory abilities.^[6]

4 Plantoid Robotics

Robots inspired by humans and animals… Sure. But plants? In 2015, a team developed the first soft robot modeled on plant tendrils. This “plantoid” emerged from the Istituto Italiano di Tecnologia, led by Barbara Mazzolai. These robots mimic the way plants avoid danger and seek nutrients without eyes or muscles. Sensors in the roots monitor temperature, humidity, light, and nutrition. These robots mimic vines in their ability to adapt to changing environments. More significantly, they can grow. Plantoids add cells to their structure using 3-D printers.

Mazzolai envisions plantoids as “a growing endoscope in the human body or even a space explorer of alien worlds.” In the future, we may find uses for plantoids in flexible supports in rehabilitation therapy, pollution monitoring, and even rescue operations. Plant roots are not the fastest diggers, but they are the most efficient ones, making plantoids a powerful tool for underground exploration.^[7]

3 Photoperiod Anticipation

Thale cress not only measures time, it divides it. This small mustard plant builds up energy reserves in its leaves during the day and consumes them at night. Researchers found that these stores decrease linearly with the length of darkness. This behavior, called photoperiod anticipation, requires complex arithmetic. Arabidopsis thaliana calculates precisely how much starch to consume so its energy reserves last the exact length of the night, maximizing metabolism and growth.

How thale cress measures and divides time remains a mystery. In 2012, Developmental Cell published research suggesting that PP2-A13 may be involved. This gene is expressed and may be required for plant survival during winter-like periods of low light. This agrees with researchers’ belief that the length of night is more important in photoperiod anticipation than hours of daylight.

When short-day-adapted Arabidopsis is suddenly exposed to a longer photoperiod, photoperiod stress occurs. This triggers a defense response with an increase in jasmonic acid, salicylic acid, and camalexin. This reaction not only reflects memory, but can actually boost resistance to pathogens.^[8]

2 Mimosa Memories

Mimosa pudica is so responsive that it is known as the “sensitive plant” or the “touch-me-not.” When stimulated, this creeper native to South and Central America closes its leaves.

In 2014, Monica Gagliano of the University of Western Australia conducted a series of experiments to test Mimosa pudica‘s long- and short-term memory. She dropped water on the plants in high- and low-light conditions. The mimosa stopped closing its leaves when it learned that the stimulus had no negative consequences.

Mimosa learned this behavior in a matter of seconds. What’s more, the plants in low-light conditions were faster learners. The more energetically costly the environment, the quicker the plants were to learn and form memories. This learned behavior lasted several weeks. Long after the stimulus had stopped and the environmental conditions changed, the mimosa’s memory appeared to remain. While these plants lack brains or nervous systems, they exhibit recall once expected only in animals. The findings are intriguing but remain controversial and in need of further replication.^[9]

1 Bad Neighbors

Chiles and fennel compete. Typically, fennel produces chemical signals that slow down the growth of its fast-growing rival. However, this is not the only way they communicate.

In 2013, Monica Gagliano blocked chemical, light, and physical contact between the plants. And yet, the chiles still sensed the presence of fennel. Chiles may use non-chemical cues—such as sound or possibly electromagnetic signals—though mechanisms remain unproven. Even without the standard signals, the chiles appeared to detect fennel and grew faster. When young chiles sense hostile neighbors, they allocate energy to their roots. Even if shielded from chemical signals, chile seeds are reluctant to grow near fennel.

When chiles sense they are near a friendly neighbor, like basil, they slow their growth. With these non-competitive plants, they put their energy into their stems rather than their roots. In experiments, the differences in germination and growth between chilies in proximity with fennel and basil were slight but significant.^[10]