The traditional view of trees and other plants as being cruder organisms than animals is being overturned by a plethora of recent research, a recent Treework Seminar in London’s Kew Gardens heard.
Researchers point to functions including breathing, digestion, problem solving, vision and even memory!
“For a long time, plants have been thought of as inferior,” said botany professor Francis Halle … but we may have been doing them an injustice. Darwin’s plant “brain”
Colleagues described how plants can detect the sound of a chewing insect, while plant roots give out a kind of click, thought to give them an idea of their spatial distribution. Roots have a very specific architecture underground that could be a sign of echolocation.
Darwin noted in 1880 that a plant’s radicle “acts like the brain of one of the lower animals”. Though it is challenging to study in real time, the root tip does have a lot of electrical activity, much like the brain, the Seminar heard.
There is also strong evidence that some plants have a primitive kind of vision – they can detect form as well as light. Leaves of the South American vine Boquila trifoliolata, for example, change shape to resemble those of its host plant in a matter of weeks.
Allied to this is spatial awareness. A wild lima bean will grow towards a nearby pole, while parasitic plants of the genus Cucscuta (dodder) always choose to grow up a tomato plant over wheat, but will take wheat over nothing. Passiflora has even been shown to anticipate the location of a slow-moving target.
Another speaker highlighted how: “Since Aristotle, we have thought of plants as insensitive, distinguished from animals by a lack of physical awareness.” In fact, said professor Monica Gagliano, plants have more genes for signalling than we do. She cited the response of Mimosa pudica to being touched: “It’s not just an instantaneous response but a learned one – and you can’t learn without memory.”
Dignity for plants
She concluded: “We don’t need more science so much as a change in the way we think about the animal/plant divide.” Taken to its conclusion, this might lead to humans having moral and even legal obligations towards plants, and in 2008 the Swiss government’s ethics committee said research proposals should consider the “dignity” of plants.
As Kew organisers noted, these are questions we don’t normally challenge ourselves with but they can certainly change our ideas about trees!