The Intelligence of Plants and Trees

“Today’s view of intelligence - as the product of a brain in the same way that urine is of the kidneys - is a huge oversimplification. A brain without a body produces the same amount of intelligence as the nut that it resembles.”

Says Stefano Mancuso, director of the International Laboratory of Plant Neurobiology in Florence who together with Alessandro Viola wrote “Brilliant Green: The Surprising History and Science of Plant Intelligence.”

Plants face many of the same problems as animals, though they differ significantly in their approach. Plants have to find energy, reproduce and stave off predators. To do these things, Mancuso argues, plants have developed smarts and sentience. “Intelligence is the ability to solve problems and plants are amazingly good in solving their problems,” Mancuso noted.

To solve their energy needs, most plants turn to the sun – in some cases literally. Plants are able to grow through shady areas to locate light and many even turn their leaves during the day to capture the best light. Some plants have taken a different route, however, supplying themselves with energy by preying on animals, including everything from insects to mice to even birds. The Venus flytrap may be the most famous of these, but there are at least 600 species of animal-eating flora. In order to do this, these plants have evolved complex lures and rapid reactions to catch, hold and devour animal prey.

Environment

Plants also harness animals in order to reproduce. Many plant use complex trickery or provide snacks and advertisements (colours) to lure in pollinators, communicating either through direct deception or rewards. New research finds that some plants even distinguish between different pollinators and only germinate their pollen for the best.

Finally, plants have evolved an incredible variety of toxic compounds to ward off predators. When attacked by an insect, many plants release a specific chemical compound. But they don’t just throw out compounds, but often release the precious chemical only in the leaf that’s under attack. Plants are both tricky and thrifty.

Scientists have discovered that plants have at least 20 different senses used to monitor complex conditions in their environment. According to Mancuso, they have senses that roughly correspond to our five, but also have additional ones that can do such things as measure humidity, detect gravity and sense electromagnetic fields.

Communication

Plants are also complex communicators. Today, scientists know that plants communicate in a wide variety of ways. The most well known of these is chemical volatiles – why some plants smell so good and others awful – but scientists have also discovered that plants communicate via electrical signals and even vibrations as well.

Many plants will even warn others of their species when danger is near. If attacked by an insect, a plant will send a chemical signal to their fellows as if to say, “hey, I’m being eaten – so prepare your defences”. Researchers have even discovered that plants recognize their close kin, reacting differently to plants from the same parent as those from a different parent.

“In the last several decades science has been showing that plants are endowed with feeling, weave complex social relations and can communicate with themselves and with animals,” write Mancuso and Viola, who also argue that plants show behaviours similar to sleeping and playing.

There is rising evidence that the radicle, or root apex, is the key to plant intelligence. Roots do not flounder randomly but search for the best positions and in some cases, will alter course before they hit an obstacle. Mancuso and colleagues recorded the same signals given off from this part of the plant as those from neurons in the animal brain.

One root apex may not be able to do much. But instead of having just one root, most plants have millions of individual roots, each with a single radicle. So, instead of a single powerful brain, plants have a million tiny computing structures that work together in a complex network. The strength of this evolutionary choice is that it allows a plant to survive even after losing 90% or more of its biomass.

We don’t even know for certain how many plant species exist on the planet. Currently, scientists have described around 20.000 species of plant. But there are probably more unknown than known. Many of these could be wiped out without ever being described, especially as unexplored rainforests and cloud forest – the most biodiverse communities on the planet – continue to fall in places like Brazil, Indonesia, Malaysia, the Democratic Republic of the Congo and Papua New Guinea, among others.
(November 2015)

Venus_Flytrap

Venus Flytrap

Illustration from Curtis's Botanical Magazine by William Curtis (1746–1799)