Stefano Mancuso’s Brilliant Green and Plant Revolution: review of two books

In my previous article, I reviewed two most recent books by the Italian plant scientist Stefano Mancuso, which covered the amazing biological talents of plants and what we can learn from them for our own and own planet’s sake.

This time, I review the two books Mancuso published previously and which I read in German translation, provided by the publisher Kunstmann (originally in Italian, these are also available in English):

• Brilliant Green
• Plant Revolution

The first book is about the sensory and cognitive capacities of plants (which do exist, albeit in a completely different form we humans are prepared to recognise as such), the second continues the plant neuroscience narrative and builds on plants’ adaptive skills to propose solutions for the human technology and environmental protection.

Unlike the most recent Mancuso books (in my case of backwards reviewing, the previous books), these two are less anecdotal, and aim to give the reader some basic knowledge about plant physiology, ecology and molecular biology. This is needed to get a grasp on how plants can perform neurological processes like sensory processing and cognition without having a brain or anything even remotely analogous. The only shortcoming is that in both these books the references are not numbered in the main text, but simply listed in the appendix.

Brilliant Green

This book was first published in 2013 under the original title “Verde Brillante: Sensibilita e intelligenza del mondo vegetale“, translated “Brilliant green: sensory perception and intelligence of the plant world”. Mancuso’s coauthor there is the science journalist Alessandra Viola.

Now, what is this nonsense, with plant intelligence, you might ask? Intelligence is defined in psychology by IQ and university degrees, but outside of it as the ability to solve problems and to learn in the process. This is something plants can do very well, without having a brain.

But then again, you might object, plants are not even able to run away from a very hungry caterpillar, doesn’t it prove they are no smarter than rocks? Well, you would start with the wrong assumption, by comparing plants to animals. Mancuso never tires of reiterating that plants are utterly different, more different than any alien life form we might imagine, and that’s it’s wrong to compare them with us. Half a billion years ago the plants chose a sessile life style where they quite literally take root and never move from the place of their birth. Which also means plants cannot run away from their predators or any other adverse situations, they can’t go elsewhere in search of food, a mate or a better environment. Moving is an approach with which animals solve most if not all problems, and while plants of course do move, they never leave the spot they quite literally hit roots. This is why plants evolved to solve problems differently. The fact that these allegedly stupid sedentary organisms have not been long ago eaten into oblivion (thus taking first the herbivores, then the carnivores with them) somehow proves that plants somehow are able to react, adapt and even defend themselves after all.

And plants do defend themselves, very efficiently actually, they also secure resources, all of which they achieve by making decisions and learning. How else can trees survive for hundreds and even thousands of years if they never learn, and respond to recurrent outside attacks and stressors with adaptations and swifter reactions, basically a form of memory? But every intelligence needs an input, and Mancuso shows that plants are even better than animals in this regard. Plants deploy many senses: smell (via volatile chemicals), taste (especially root tips), touch (many trees avoid growing into each other’s foliage), light perception of course (needs no explaining), and even hearing (apparently, even this!), plus many others, the Florentine professor speaks of 15 senses, e.g. for gravity, water, oxygen, salinity, chemicals (both useful and noxious). A plant uses those sensory inputs for signal transmission inside the plant and outward communication with organisms around it, like other plants, but also with animals and fungi. And of course, plants also sleep, again in their own way.

Plants perform quite complex cognitive tasks in a kind of swarm intelligence manner. The reason why plants don’t have a brain as we animals do is not due to their stupidity or their dull lives, but due to the simple fact that exactly because of their sessile nature plants can’t run away from an attack. They must be constantly able to sacrifice parts of their body, and this is exactly why many plants can even survive being burned. Their modular bodies are built in a repetitive fractal way, all functions are distributed over the entire plant, instead of being concentrated in unique or pairwise organs like with animals.

Plants can smell without a nose, taste without a tongue, touch without hands and perceive light without eyes, although some people note that leaf epidermis cells are built as tiny lenses and wonder if plants can actually “see” shapes). Plants can also hear without ears (they have no music preference, but do react positively to certain sound frequencies), and Mancuso also wonders if the clicks of rupturing cell walls of growing roof tips can actually be acoustically perceived by other root tips and neighbour plants, which would reveal a new world of plant communication.

Plant neurobiology:Integrated view of plant signaling (above & below) ground 🌱 #PlantScience https://t.co/0RALmyuD7v pic.twitter.com/crr5laNQgg

— Cory Cowan🌱🔬 (@CoryLCowan) July 29, 2016

Plant neurobiology is a thing, if you are still not convinced because of their lack of neurons: plant cells also generate electric action potentials in their xylem which can send a signal from a root tip all the way to the leaves of a tree. For example, if the root tips report lack of water, the plant must close its leaf stomata up in the foliage to prevent further evaporation. But then again, with stomata closed there will be no more CO₂ available for photosynthesis. A plant will need to make a decision how to proceed, and while plants may not “think” as fast as animals, they do decide, and their decisions are always the best ones.

Especially the root tips of plants are something truly fascinating and the best subject to understand plant cognition. These seem to really work as ants or termites in a swarm intelligence colony, each one rather simple on itself, but with millions of them for one single plant (trees may have billions of root tips) a gigantic computational power emerges, capable of the most complex cognitive decisions. This process is called Emergent Properties, and this is apparently how plant neuroscience and plant intelligence happens. It’s not like Mancuso is the first to see the root ball of a plant as its brain: various scientists of the past, including Charles Darwin, thought the same.

Its task sounds simple: a root tip must grow towards the resources, away from stressors like light and around obstacles like stones. But which resources should the root tip go for? Water, nitrates, phosphates, minerals, air (plants breathe via roots) etc? These different necessities are most definitely not to be found in the same direction, sometimes exactly the opposite. This is where the swarm intelligence of the millions of root tips, each capable of processing local information for many parameters and of sending signals upwards inside the plant and around them in the soil, electrically, chemically, and maybe even acoustically, comes into play. The emergent property is here that a plant knows exactly which root tip has to grow towards which resource.

Above the ground, similar thing happens. Plants perceive their neighbours and interact with them via volatile chemical compounds, touch and other senses. They can warn their neighbours of predators (especially the very hungry caterpillars) and take defensive measures themselves. One leaf may be very stupid and easily munched or drained by an insect, but the whole plant is definitely not stupid.

At some point Mancuso even strays in human neuroscience and suggests that our brains operate similarly, a collective “emergent property” activity of neurons generates a cognitive process which results in a decision. Emergent properties is what makes the modular plant organisms, which are not indivisible individualisms like us animals, but rather clonal colonies, each bud on a tree like a polyp on a coral, very smart.

All this evolved because the sessile lifestyle of every plant is something animals (named after the Greek word describing movement) generally don’t comply with. But I wonder if maybe the lifestyle of some families among cnidaria (sea anemones and corals) is similar to that of plants in a way (corals even contain symbiotic algae for photosynthesis). In this regard, maybe it would be good if Mancuso one day compares notes with some zoology colleagues, for example to cross-check the biological adaptations of a sea anemone and a stinging nettle!

Plant Revolution

This book was first published in Italian in 2017 under the title: “Plant Revolution: Le piante hanno gia inventato il nostra futuro“, meaning that plants have already invented our future. And this is what the book is about, the inspirations our technology and civilization can take from plants.

The book is a kind of sequel to Brilliant Green, further expanding on the topic of plant neuroscience, this time with illustrations. There is even more about the cognitive strategy of swarm intelligence which is slower, but at the end more efficient. Mancuso does not have much admiration for human obsession with logic and hierarchical order, he has stories in this regard, both personal and of famous people proving these do not really work as intended but create a mess instead.

Not all plant reactions are slow though. The insect-eating plant like venus flytrap shuts its leaves swiftly, and only when the plant is sure the object is indeed edible and already inside, so it won’t escape. Humans were also always fascinated by the mimosa plant, which is famous for its rapid reaction of leaf folding when touched or shaken ever so slightly. Mancuso also reminds of an old experiment with mimosa, once performed by an assistant of Lamarck, and repeated under more controlled conditions by the book author’s own lab. Being shaken or dropped makes the mimosa to close its leaves. And yet, when the stress is repetitive, the plant learns not to react to it anymore, and remembers the lesson even a month later (Gagliano et al 2014).

The book has other amazing stories about plants. Like the Chilean plant Boquilla trifoliata which can imitate the leafs of other plants it grows next to (Gianoli & Carrasco-Urra 2014), for reasons not entirely clear. There is also currently no viable explanation how this plant knows which leaf shape it must form, the hypotheses include horizontal gene transfer or the sense of smell, via volatile organic compounds. Mancuso recalls the possibility that plant epidermis cells can function as tiny lenses and wonders if B. trifoliata can actually see the leaf shapes it then emulates.

There are also amazing stories of plant evolution, like that of rye, which was originally a weed contamination of the wheat which humans just started to cultivate in the (then) fertile crescent of the Middle East. Each meddling rye grain was selectively discarded by early farmers, so the plant responded by evolving its grains to match those of wheat. When human agricultural tradition expanded up north, rye proved to be the one growing best under the harsher conditions, and soon became the key bread crop in the area of central and eastern Europe. Rye basically self-domesticated itself, something we generally associate with cat and dog evolution.

Or the story of amaranth, which we hipsters know as a very expensive (pseudo) grain you only get in an organic shop. Well actually amaranth is a weed also, and it pollutes the giant American fields of soy and corn, the staple supply of the US meat industry. The American solution was of course to plant RoundUp-Ready GMO crops and dump enormous amounts of glyphosate, killing everything except the genetically resistant crops. Guess what. Amaranth evolved a glyphosate resistance and continues spoiling everything.

But as it is with all Mancuso books, he soon discusses human civilization. Specifically, how plants with their modular assembly and low energy requirements can provide technical solutions for humanity and save the planet from the climate and ecological disasters. I this regard, he derives much inspiration from plant movements. Yes, plants of course move, as time-lapse films have proven long ago. Their movements are just too slow for us to perceive (except of mimosa or meat-eating plants), but this is not a handicap at all. First of all, plants live on a different time scale than animals (some trees grow to be thousands of years old). Second, plants, being sessile anyway, don’t need to move fast, but it sure pays off to conserve energy. And plants are masters in performing movements sometimes without any energy input whatsoever, using dead tissues.

For example, pine cones can open up and certain seeds (Erodicum cicutarium) can even crawl and dig themselves in by drawing energy from changes in air humidity during day and night. Sure, the movement is slow, but if you wish to send a robot into space to explore planets like Mars, speed is less relevant than energy efficiency. Hence the idea of Plantoids, plant-inspired robots which are built like plants and operate like plants. Instead of investing into high-tech robot with controlled navigation where many things can go wrong rendering the entire landing project a failure, plantoids should be rather deployed as swarm of many cheap and simple modules, to cover a large territory while allowing for loss of some or even many of them. The project was funded by EU Commission as part of the FET programme, also European Space Agency (ESA) was interested.

Other space exploration ideas are being discussed, like growing crops on Mars or even in spaceships. Which is not trivial, because gravity is very important for plants and gravitropismus is one of their key senses. In this regard, Mancuso talks about his and his colleagues experiments on parabolic flights by ESA, where they did measure rapid action potentials and other physiological responses in root tips under microgravity.

The books turns to various ways to draw inspiration from plant design, not just for space travel. Mancuso tells of success stories like the giant water lilly Victoria amazonica, whose 3 meter wide and extremely robust leaves served as the inspiration for the structure of London Exhibition’s Crystal Palace in 1851. The book ends with the story of the Jellyfish Barge.

Jellyfish Barge was co-invented by Mancuso together with other Italian scientists, architects and engineers. It is an octagonal floating greenhouse where vegetables can be grown at sea, entirely without any energy input (except the sunlight), and even without any freshwater. This is because solar panels provide the energy required to desalinate seawater by evaporation. Upscaling can be done like everything else in plants: by docking more Jellyfish Barge modules together. Despite being extremely eco-friendly, the concept failed to attract industrial investors so far. Which I kind of understand, there is no short-term money to be made in saving the planet, but truly unlimited amounts of it in destroying the planet.

Again, Mancuso books are highly recommended. Once we stop looking at plants as a inanimate objects, we will recognise how fascinating and evolutionary successful they are, capable of amazing adaptation and intelligent low-energy solutions to very complex problems.

Disclaimer: As usual, I receive no payment or incentive to write this review, but I did receive the books gratis from the publisher upon request

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