The Secret Lives of Plants

Let’s face it: At first glance, plants don’t seem to lead very interesting lives. How much can a brainless organism that’s stuck in one place really do? Quite a lot, it turns out. Research shows that plants detect and respond to changes in the world around them. They maintain busy social lives, sharing resources and important news with others through complex networks. And they have highly developed senses much like our own.

“Plants can track almost everything happening in their environment,” says Heidi Appel, an ecologist at the University of Toledo in Ohio. “This involves all the same basic senses we have—seeing, hearing, touch, taste, and smell—plus some others.” Here’s what Appel and other scientists have discovered about the secret lives of plants.

Let’s face it: Plants don’t seem to lead very interesting lives. A plant doesn’t have a brain and is stuck in one place. What can it really do? Quite a lot, it turns out. Research shows that plants notice and act on changes in the world around them. They have busy social lives, sharing supplies and important news with others through complex networks. And they have highly developed senses much like our own.

“Plants can track almost everything happening in their environment,” says Heidi Appel. She’s an ecologist at the University of Toledo in Ohio. “This involves all the same basic senses we have—seeing, hearing, touch, taste, and smell—plus some others.” Appel and others are studying the secret lives of plants. Here’s what they’ve found.

Appel first became interested in whether plants could hear while talking with her colleague Rex Cocroft, who studies insect communication. He complained that the noisy chomping of a caterpillar was drowning out other bug sounds he wanted to record. “It was an ‘Aha!’ moment for us,” she says. They wondered if plants could also hear and respond to the chewing.

To find out, the scientists recorded vibrations of a caterpillar eating leaves and played the recording back to some plants but not others. Plants exposed to the munching sound produced more chemical defenses, substances that taste bad to bugs. Many plants use these chemicals to avoid being eaten. Other sounds, such as wind blowing, had no effect. “Plants respond selectively to sounds that are important to them,” says Appel. They ignore sounds that don’t pose a threat.

Appel remembers when she first became interested in whether plants could hear. She was talking with her colleague Rex Cocroft, who studies insect communication. He complained about the noisy chomping of a caterpillar. It was drowning out other bug sounds he wanted to record. “It was an ‘Aha!’ moment for us,” she says. They wondered if plants could also hear and respond to the chewing.

To find out, the scientists recorded vibrations of a caterpillar eating leaves. They played the recording back to some plants but not others. Plants exposed to the munching sound did respond. They produced more chemical defenses, substances that taste bad to bugs. Many plants use these chemicals to avoid being eaten. Other sounds, such as wind blowing, had no effect. “Plants respond selectively to sounds that are important to them,” says Appel. They ignore sounds that don’t pose a threat.

Plants are able to sense other things besides sound. “They don’t have noses or tongues, but they’re very tuned in to chemicals in their environment,” says Rick Karban, an ecologist at the University of California, Davis. “And they don’t have eyes, but they’re very sensitive to light.” Plant tissues contain photoreceptors. These molecules allow them to tell how bright the light is and which direction it’s coming from.

Plants can sense other things besides sound. Rick Karban is an ecologist at the University of California, Davis. “They don’t have noses or tongues, but they’re very tuned in to chemicals in their environment,” he says. “And they don’t have eyes, but they’re very sensitive to light.” Plant tissues contain photoreceptors. These molecules allow them to sense the brightness of light and which direction it’s coming from.

We may not think of plants as chatty, but they communicate in a complex language of chemicals. Karban studies what happens when hungry insects injure sagebrush plants. “When a plant is attacked, it emits chemical cues into the air,” he says. “Its neighbors detect those cues and increase their defenses.”

We may not think of plants as chatty, but they communicate. They use a language of chemicals. Karban studies what happens when hungry insects hurt sagebrush plants. “When a plant is attacked, it emits chemical cues into the air,” he says. “Its neighbors detect those cues and increase their defenses.”

Plants can prepare for an onslaught of bugs with not only chemical defenses but physical ones as well. Their tissue becomes tougher, making it harder to chew. And they can grow stiff hairs that thwart insects.

Some plants can even tell what kind of insect is eating them based on chemicals in the bugs’ saliva. Depending on the attacker, plants release different alarm signals and adjust their defenses.

Chemicals aren’t the only defenses plants use to prepare for a bug attack. They use physical defenses too. Their tissue becomes tougher, making it harder to chew. And they can grow stiff hairs that get in a bug’s way.

Some plants can even tell what kind of insect is eating them. Chemicals in the bugs’ saliva tip them off. Plants release different alarm signals for different bugs. They change their defenses.

Trees may seem like the most solitary and unchanging plants of all. But they busily interact with their environment and their neighbors.

Trees might seem like the most unchanging plants of all. But trees are busy too. They interact with their surroundings and neighbors.

The biggest, oldest trees have the most network connections. Simard calls them “mother trees.” They help youngsters grow, and they take special care of their families. Networked trees can chemically identify relatives, such as siblings or offspring. They send those seedlings extra food, nutrients, and water. If a tree in distress signals for help, nutrients or defensive chemicals arrive within hours.

“We’ve barely scratched the surface of the language of trees,” says Simard. “Their conversations and exchanges are so complex.”

The biggest, oldest trees have the most network connections. Simard calls them “mother trees.” They help young trees grow, and they take special care of their families. Through the network, trees can identify relatives. Chemicals tell them which trees are their siblings or offspring. The trees send those seedlings extra food, nutrients, and water. If a tree is in distress, it signals for help. Nutrients or defensive chemicals arrive within hours.

“We’ve barely scratched the surface of the language of trees,” says Simard. “Their conversations and exchanges are so complex.”

Some researchers even think plants may be intelligent, in a way. “They’re collecting information about their environment and using it to make decisions that benefit them,” says Karban. “If that process counts as intelligence, there’s more and more evidence that plants are exhibiting it.”

Some studies even suggest that plants may have a kind of memory of past events—such as bug attacks or cold snaps—that helps prepare them for future challenges. Plant scientists are still debating whether it makes sense to use terms like memory and intelligence for organisms without a brain. But there’s one thing they agree on, says Appel: “Don’t underestimate plants!”

Some researchers even think plants may be smart, in a way. “They’re collecting information about their environment and using it to make decisions that benefit them,” says Karban. “If that process counts as intelligence, there’s more and more evidence that plants are exhibiting it.”

Some studies suggest that plants may have a kind of memory of past events, such as bug attacks or cold snaps. This helps prepare them for future challenges. Does it make sense to use terms like memory and intelligence for living things without a brain? Plant scientists are still debating. But there’s one thing they agree on, Appel says: “Don’t underestimate plants!”