Published On: Mon, Sep 9th, 2019

Do Plants Have a Brain?

Plants may be the most underappreciated life forms. Since they can’t move like animals, they’re usually considered simple environmental bystanders –– soaking up sun, providing oxygen through photosynthesis, providing the many fruits and vegetables we eat but otherwise living a passive existence.

Yet, scientific research is revealing so many under-recognized plant abilities, some are theorizing that plants actually have a “brain.” For example, plants can defend themselves against predators but also attract desirable visitors –– pollinators. They can communicate with other plants through their root systems and, according to some research, listen, count, remember, know their kin and feel emotions like pain.1

Certainly, plants don’t have the walnut-sized brain formations we associate with animals. But electrical and chemical signaling systems exist in plants that are analogous to those in animal brains replete with neurotransmitters like serotonin, dopamine and glutamate.2

The intelligence or brain of plants, say some scientists, may be like the distributed intelligence seen in the swarming of birds or insect colonies in which each individual has a part to play for the intelligent behavior of the whole. They are all part of the “brain.”

The ‘Brainy’ Venus Flytrap

Many have heard of the carnivorous Venus flytrap found in subtropical wetlands and also found in North Carolina and South Carolina.3 This plant traps its prey with leaves lined with “teeth” that clamp together like a clamshell, after its sensitive hairs are triggered and convey to them that food might be present.4

Contrary to its name, the Venus flytrap primarily eats ants, but also eats flies, beetles, slugs, spiders and even tiny frogs.

How “smart” is the Venus flytrap? When triggered, its trap stays slightly open for a few seconds to allow the escape of very small insects which will not provide enough food to justify the work required to digest them. (The plant secretes digestive juices, similar to those of humans, in a process that takes five to 12 days.)

The plant will also not close on a dead insect, one that doesn’t move, presumably because it will offer less nutritional value.5 In a TED talk, neuroscientist Greg Gage reveals that the Venus flytrap can actually “count” and, on the basis of how many times its sensitive hairs have been triggered, will “decide” whether the visitor is an actual insect and whether or not to close on it.6

It seems to be ruling out “false positives,” says Gage. Some researchers have ascertained that the decoded complete DNA sequence of the Venus flytrap is virtually the same size as the human genome.7

Another Brainy Plant Is the Mimosa Pudica or Sensitive Plant

Mimosa pudica is often called the “sensitive plant” because when its fern-looking leaves are lightly touched, they rapidly fold up and close. If you tap a leaf harder, the entire branch seems to fall down as demonstrated in Greg Gage’s TED talk. This amazing behavior could have evolved to scare away insects or make the sensitive plant less appealing to herbivores, he postulates.

Who says plants don’t move? Like the Venus flytrap, the sensitive plant not only moves –– it moves quickly. There is more to indicate the remarkable sensitive plant may have a brain. When Monica Gagliano, an animal ecologist at the University of Western Australia, conducted experiments on the plant, here is what happened writes Michael Pollan, in the New Yorker.8

“Gagliano potted fifty-six mimosa plants and rigged a system to drop them from a height of fifteen centimetres every five seconds. Each ‘training session’ involved sixty drops. She reported that some of the mimosas started to reopen their leaves after just four, five, or six drops, as if they had concluded that the stimulus could be safely ignored.

‘By the end, they were completely open,’ Gagliano said. ‘They couldn’t care less anymore.’ Was it just fatigue? Apparently not: when the plants were shaken, they again closed up.

‘Oh, this is something new,’ Gagliano said, imagining these events from the plants’ point of view. ‘You see, you want to be attuned to something new coming in. Then we went back to the drops, and they didn’t respond.’

Gagliano reported that she retested her plants after a week and found that they continued to disregard the drop stimulus, indicating that they ‘remembered’ what they had learned. Even after twenty-eight days, the lesson had not been forgotten.”

When Gagliano’s scientific colleagues scoffed at her conclusions that the sensitive plants were exhibiting intelligent, brain-like behavior, she reminded them that in similar experiments with bees, the insects forgot what they had learned after just 48 hours! No one doubts that bees have brains.

Other Smart Plants — Pitcher Plants

Even more “brainy” than the Venus flytrap or sensitive plant are pitcher plants, which feature deep cavities filled with digestive liquid that attracts and then drowns their prey.

Most pitcher plants are found in tropical environments but some are present on the U.S. Eastern Seaboard, Gulf Coast, the Great Lakes region, Washington state and Alaska.9 Here is how ZME Science describes the pitcher plant’s ingenious actions.10

“The Asian carnivorous species of plant from Borneo are called pitcher plants, due to their cup-shaped traps for the insects which resembles a pitcher. Pitcher plants can easily capture and trap ants due to the plant’s margins that become wet and very slippery.

When the prey walks on the edges of the flower, it falls inside the cup and is trapped there. But this plant has developed a different strategy – instead of eating one ant at a time, it devised a strategy to eat more insects in one meal.

The plant can make its edge slippery or safe, and it does so depending on what it wants. ‘The plant’s key trapping surface is extremely slippery when wet, but not when dry,’ explained project leader Ulrike Bauer of Bristol University’s School of Biological Sciences.

‘For up to eight hours during dry days, these traps are switched off and do not capture any of their insect visitors. At first sight, this is puzzling because natural selection should favor traps that catch as many insects as possible.’

The thing is, ants don’t all march in at once – they have individual scouts that go ahead and see if a route is safe. If the scouts find that the plant’s edge is not slippery, they come in with nectar. Pretty soon, the ants will return in bigger numbers to retrieve more nectar, but they will have a sad surprise – the edge of the plant has become slippery again, trapping many of them in one go.

So the plant chooses to let the scouts go and lure in more ants to feast upon. The plant’s strategy appears to be extremely successful, biologists report.”

More Pitcher Plant Ingenuity

Pitcher plants have also evolved a unique relationship with bats. They attract bats to roost and defecate to fertilize them by attuning to the bats’ specific echo-generating calls and thus luring them. However, the pitcher plant does not eat the bats. It has other uses for them. Here is how The New York Times describes the symbiotic relationship that has developed between bats and some pitcher plants:11

“By the looks of it, Nepenthes hemsleyana, a pitcher plant in the peat swamp forests of Borneo, is gradually shrugging off meat eating in favor of the nitrogen-rich offerings of an insectivorous bat.

As reported in the July issue of Current Biology, Michael Schoner of the University of Greifswald in Germany and his colleagues found that the Hardwicke’s woolly bat and the pitcher have entered a mutually satisfactory partnership.12 The plant offers the bat a perfect place to roost, and the bat fertilizes the plant with its feces.

Weighing barely more than a penny, the bat fits in the pitcher ‘like a cork in a bottle,’ said Mr. Schoner, a doctoral student.

The pitcher plant advertises its accommodations through a special concave structure along its orifice that reflects the bat’s sonar signal from many angles, making the roost easy to find; and it keeps its pool of digestive juices well below the space where the bat cocoons itself.

Bats love their pitchers, and not just for sleeping. ‘We’ve found bats copulating inside,’ Mr. Schoner said. ‘Also, mothers that have given birth to their babies.'”

Attracting Visitors in Clever Ways

Many realize that the physically attractive and fragrant flowers of plants draw bees, hummingbirds and other pollinators to them –– which seems to be the point of the visual and olfactory cues. But some plants have another way to “lock in the loyalty” of pollinators, says a study in Science.13

These plants manipulate the memory of bees by emitting caffeine, a psychoactive drug they can produce. The caffeine is said to prompt bees to remember a particular plant and return to it, making them more loyal and dependable pollinators. Here is how Science describes the phenomenon:14

“A key challenge in floral advertising is that signals must be not only attractive but also memorable: The more distinct a flower signal, the more likely a pollinator is to remember it, increasing the probability that pollinators will visit more flowers of this species while ignoring competing flower species.”

Repelling Visitors in Clever Ways

Plants have many ways of repelling visitors too –– defending themselves by warding off visitors. For example, both the sand verbena and the honey-scented pincushion coat themselves in sand, which protects them from damage from herbivores.15 And who has failed to notice that beautiful roses are surrounded with puncture-capable thorns that keep herbivores and even humans at a distance?

Plants can also alter the taste or texture of their leaves to produce toxins that make them less appealing to herbivores. For example, acacia trees are reported to produce bitter tasting tannins that make their leaves unappetizing and difficult to digest to nibbling antelopes.16

With their many subtle and not-so-subtle survival mechanisms, it is hard to believe plants do not have a brain –– albeit manifested differently than what we see in animals. They certainly exhibit intelligence, creativity and awareness of their surroundings.