Though plants possess nothing even remotely like brains, they can nevertheless communicate, measure time, and even use camouflage. They may not be thinking in a way that we'd recognize, but our chlorophyll-saturated pals are certainly doing a lot more than sitting around splitting water molecules. Here are ten things plants do that look pretty damn smart — even to those of us over here in the Kingdom Animalia.
1. Plants communicate with insects
As we've mentioned on io9 before, some plants have evolved a survival strategy that involves the chemical equivalent of sending out a distress call. When tobacco plants are attacked by caterpillars, they release a chemical into the air that attracts predatory bugs who like to eat caterpillars. So the nice smell you get from crushing up leaves may actually be the plant's way of asking its insect buddies to come bite your head off.
2. Plants have memories
Certainly plants don't "remember" the way humans do, but a group of researchers discovered that plants learn to associate various wavelengths of light with different kinds of danger. The scientists would shine light on plants for an hour, then expose them to a virus. This was a pathogen the plants could protect themselves from by manufacturing a particular chemical. What the scientists discovered was that the next time they shone light on the plants for an hour, its leaves began to manufacture the chemical necessary to fight the virus. It didn't manufacture the chemical at other times — only when exposed to the same kind of light for the same amount of time. The scientists speculated that perhaps plants have developed this "memory" because each season brings with it a change in the light — as well as changes in the kinds of pathogens likely to attack the plants. So from an evolutionary perspective, a plant that learns to associate light duration with certain pests is going to survive longer.
3. Plants create communication networks
Plants don't just yell for insect help when attacked — they also warn each other of impending doom. Strawberry, clover, and other ground plants grow by sending out "runners," horizontal stems that eventually bud into their own plants. These runners create simple communication networks between the connected plants. When one plant in a network is attacked by a bug, it sends out a warning to the network so that its siblings can build up defenses against the invaders — ranging from toxins to chemicals that simply taste really bad to herbivores.
4. Plants grow differently in response to sound
We may have to stop mocking gardeners who talk to their plants: University of Western Australia biologist Monica Gagliano found that corn plants could emit and respond to sound. Gagliano noticed that the roots of corn plants made clicking noises at around 220 Hz. She and her collaborators then grew corn suspended in water and played an artificially generated, continuous noise at 220 Hz. The roots responded to the noise by leaning towards the source of the sound. It's not clear why plants would evolve the ability to hear and emit sound, but Gagliano and her colleagues are trying to find out by gathering more data.
5. Plants measure time
How do you think plants know when to flower? That's right — they're keeping track of time. Scientists have recently identified a set of proteins in plants that respond to the amount of light they're exposed to during the day. When they receive enough light per 24 hour period, these proteins send a signal that activates the flowering cycle.
6. Plants know up from down
Are you one of those people who likes to screw around with plants by sticking them into the ground upsidown or sideways? Well plants don't give a fuck, just like honeybadgers. No matter how they are positioned, plants will aim their roots downward, into the ground. It's likely that they sense gravity, just the way their ambulatory cohorts do.
7. Plants know who is family and who isn't
It seems that plants can recognize kin. Explains Wired's Brandon Keim:
In a paper published in the November American Journal of Botany, [biologist Susan] Dudley describes how Impatiens pallida, a common flowering plant, devotes less energy than usual to growing roots when surrounded by relatives. In the presence of genetically unrelated Impatiens, individuals grow their roots as fast as they can.
Apparently plants recognize their relatives via chemicals exuded from their roots, and choose to share available nutrients with them.
8. Plants warn each other about approaching enemies
It seems that tobacco plants are pretty communicative. Not only do they call in their insect allies when attacked, but they also prepare for battle themselves when receiving chemical warnings from neighboring sagebrush. To discover this, scientists clipped some sagebrush, and observed that tobacco plants living downwind were eaten by herbivores far less often than they would be ordinarily. Apparently the tobacco had heeded the sagebrush's "danger" warnings, sent via windborne chemicals, and manufactured some defensive chemicals that made their leaves less tasty.
9. Plants use camouflage
As tobacco plants have taught us, one of a plant's best defenses is to make itself less tasty. The Mimosa pudica has a unique way of doing this. Instead of using chemicals to produce a nasty flavor, the plant curls its leaves up in response to touch. Scientists believe this is a defense to make the plant's leaves appear smaller and less succulent. Herbivores looking for a nice, leafy snack will go seek it elsewhere.
10. Plants are escape artists
Light provides plants with energy, a system for telling time . . . and an impetus to grow big enough to escape the confines of shade. Plant biologist Joanne Chory recently identified the exact protein that triggers stems and stalks to grow taller. The protein, called PIF7, senses the arrangement of light around the plant — and if the plant is in shade, will spur the entire plant to grow taller and seek sun. Chory says that she hopes to use PIF7 to push crops to grow larger and "thus produce more food or feedstock for biofuels and biorenewable chemicals."
Sources linked within the article. Top photo by Sebastian Duda, via Shutterstock.