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Six reasons plants are cleverer than you think

In Is Eating Plants Wrong? botanist James Wong discovers that plants are capable of things that used to be thought the preserve of animals, or even humans. He speaks with plant scientists from around the world whose research has led them to conclude that plants can communicate, learn, and even remember. Some even go as far as to say plants are intelligent.

1. Plants communicate through fragrances

Plants can communicate by emitting scents called volatile organic compounds through the air. These scents are picked up by other parts of the same plant, or by neighbouring plants, who then react to them, change their defences, and as a result receive less chewing damage from the different insects that nibble their leaves.

So if a leaf is being eaten by an insect or a caterpillar, the plant releases a warning scent, which nearby leaves pick up, and act on by emitting a different compound to repel the insect, or to attract predators of the nibbler like birds or wasps to come and eat it.

2. Sagebrush shrubs have regional dialects

Professor Rick Karban of the University of California at Davis found that sagebrush shrubs are more effective at communicating with neighbouring plants, than with those growing over two hundred kilometres away. The sagebrush plants use different regional dialects for communication!

In a scientifically rigorous experiment, they found that the southern sagebrush shrubs did not respond to cues from their northern cousins as much as to those from southern plants, and vice versa. The shrubs don’t seem to understand their distant cousins as well as their neighbours. Professor Karban and his team were able to measure and confirm this by using both northern and southern sagebrush clippings in both northern and southern locations, to make sure it’s actually the dialect that’s different, and not the topic of conversation, as it were.

3. Plants can learn to associate a sound with “food” (a light source) like Pavlov’s dogs

The Russian scientist Ivan Pavlov famously found that his dogs learned to associate the sound of a bell with the arrival of food. He would ring a bell before serving them their meal, and the animals came to salivate at the mere sound of the bell, before dinner was dished up.

Dr Monica Gagliano of the University of Western Australia tried a similar test with pea seedlings and found that the plants did indeed learn to associate sound with food! The plants learned to make an association, remembered it, and acted upon it. Which led Dr Gagliano to ask, “who is making the choice?”. “Who”, not “what”!

How these peashoots make decisions

Dr Monica Gagliano of the University of Western Australia explains.

How plants communicate

If potted in a row, sharing roots in each pot, plants can play Chinese whispers.

4. Plants can play Chinese whispers and remember the message

Plants can communicate through substances they emit through their roots, as well as through fragrances sent out from their leaves. And if potted in a row, sharing roots in each pot, they can play Chinese whispers. They can pass a message from the first root of the first plant down to the last plant in the same row of pots. And they can remember the passed-down message, and act on it when necessary!

5. Trees feed their relatives

Trees can share nutrients, and do that more with kin, than with unrelated trees. In any given patch of forest, the trees are all connected to each other through an underground fungal network, with fungi linking the trees’ roots in a symbiotic system called mycorrhiza. A pioneer of this aspect of plant science, Prof Suzanne Simard, has dubbed this the “wood wide web”. She has observed that trees pass both information and nutrients to each other through the mycorrhiza.

What’s more, they can distinguish between related and unrelated trees, and, for example, send more carbon to their kin than to strangers! It seems to be that trees really do have a preference for sharing with kin, and that it’s the tree making that choice, not the fungus. Dr Brian Pickles of the University of Reading, who collaborates with Prof. Simard, tested this on tree seedlings. He potted them together with both full siblings and unrelated seedlings. In a lab, not a fungus-rich forest soil. And indeed the siblings shared more with each other than with the strangers! The difference was small, but potentially enough to tip a seedling from the dying category into the surviving category.

The wood wide web: how trees share with their kin.

Dr Brian Pickles explains how trees share with their relatives.

6. Plants can sense more than we can

Plants don’t have brains, and yet without brains, and without neurons even, they can do many things that we need brains and sensory organs for.

So without eyes plants can perceive a lot of information about light, without noses they can perceive chemical information like smells, without ears they can perceive the vibrations of sounds. Plants are very perceptive about what’s going on in their environments. They can sense touch, and taste, too, for example they can identify herbivore predators nibbling their leaves from the taste of the herbivore’s saliva.

So plants have the same five senses humans have? “And then some,” says Prof. Rick Karban. Namely plants can also perceive electrical signals, temperature, electromagnetic forces, heavy metals, pathogens, gravity and more.

Listen to Is Eating Plants Wrong? with botanist James Wong to learn more.