Sprout of the ordinary: Have we completely misunderstood what plants are?
It turns out they are territorial, almost clannish. Certain vines can make caterpillars eat each other. How did we miss all this? Take a look.
Botany is a field in turmoil, says Atlantic writer and climate science journalist Zoe Schlanger (who has a degree in environmental studies, journalism and politics from New York University).
Her new book, The Light Eaters (HarperCollins), examines the latest epiphanies, and how they are prompting researchers to rethink how they view their subjects.
What kind of “intelligence” allows vines to blend their leaves into the shrub on which they climb? How do tomato plants manufacture their own insect repellent, and then communicate to their neighbours that it’s time for them to do the same? How does a pea seedling “hear” water flowing and make its way towards it?
Given that there is now evidence of “intent” behind these actions — where earlier they were seen as accidents of circumstance or autonomous response — researchers are asking deeper questions too. Do plants have social lives, and hierarchies? Do they have memory? What about personalities?
Schlanger’s book draws together strange answers, and strange new questions, from the labs and field notes of researchers around the world.
The very hungry caterpillars
In 2017, it was found that tomato plants, which produce a chemical called methyl jasmonate (MeJA), could spark cannibalism in caterpillars (who do tend to eat each other in nature, but typically not when other food is freely available).
Emitted as an airborne signal, the MeJA also served to warn neighbouring plants that the ravenous bugs were near.
As the caterpillars started feeding on each other, other tomato plants nearby began to emit this chemical too, states the report by researchers at University of Wisconsin-Madison, published in Nature Ecology and Evolution.
Meanwhile, a 1991 study published in the journal Phytochemistry found that plants such as lima beans used a similar mechanism, releasing volatile organic compounds to summon the caterpillar’s specific predators, such as wasps and ants. (It’s like the start of a botanical horror film!)
Not in my backyard
Plant behaviour can be territorial. In 2018, new research began emerging about how ferns protect their home ground, Schlanger writes. Researchers at Colgate University in New York found that they can emit a hormone that slows the rate at which sperm from neighbouring ferns swim through water (fern sperm must swim through water to propagate).
The sabotaging fern can enjoy more of whatever is scarce, be it water, sunlight or soil. ““This is brand new,” Eric Schuettpelz, a research botanist at the Smithsonian’s National Museum of Natural History in Washington, DC, told me over the phone,” Schlanger writes. ““We know it’s the plant hormone but no idea how it works,” Schuettpelz said. How did a fern know it was beside some fern competition? How did it time its malevolent release?”
The friends and family plan
Plants have been found to be familial. Research by entomologist Richard Karban of the University of California, Davis, published in 2013 in the Proceedings of the Royal Society B: Biological Sciences, has shown that species of sagebrush found on the mountainside of Mammoth Lakes were more likely to heed chemical warnings wafting through the air, if they came from close family members (plants that had emerged from the seeds of this parent plant).
Scientists from the University of Turku in Finland, Ryukoku University in Japan and Cornell in USA, meanwhile, found that, when munched on by predators, goldenrods in a hospitable environment used incredibly specific chemical alarms that could be deciphered only by close kin. The same species, in more hostile regions, sent out signals that could be understood by a wider array of plant species.
The inference made, Schlanger writes, was that “when times are truly tough, you don’t want to be left standing in a field alone when it’s over, if you’re a plant. There’ll be no one to mate with, no one to help bring in pollinators. It’s the closest scientists have come to showing intentionality in plant communication.”
Root causes
Why has it taken this long for researchers to notice these behaviours? A key reason is that plants exist on a much slower timescale than our own, Schlanger writes.
As a result, humans suffer from what, in botany circles, is called plant blindness: “the tendency to view plant life as an indistinguishable mass, a green smudge, rather than as thousands of genetically separate and fragile individuals, as distinct from one another as a lion is from a trout.”
“This is precisely why it is important to understand plants as individuals in the way botanists are doing now,” says Prasanna NS, a botanist and TN Khoshoo Postdoctoral Fellow at the Ashoka Trust for Research in Ecology and the Environment (ATREE), in Bengaluru. “It brings in new perspective and lets people engage with plants through their unique behaviours, beyond their umbrella settings such as forests or grasslands.”
It’s important not to overdo things though, Prasanna points out. “When it comes to botany, things can go down a very slippery slope, as they did in the 1970s, with The Secret Life of Plants,” he says.
That 1973 book by journalist Peter Tompkins — cited as an example of what not to do, in Schlanger’s book too — drew on controversial, pseudoscientific experiments, and then oversimplified them, to suggest that plants could “feel” and “hear” and “enjoy Beethoven”. It suggested that they could read minds and respond to polygraph tests. It was all just a “beautiful collection of myths,” Schlanger writes.
The book set the field of botany back by decades, as researchers became wary of broaching the idea of any kind of “plant intelligence”.
This must not happen again, Prasanna says. “We must be careful not to anthropomorphise these behaviours as we have done with animals — and we shouldn’t have done it there either.”
