Kin recognition is important for the social behavior of most animals. Animals tend to behave in ways that benefit their relatives, often at a loss to themselves. Some common examples are honeybees, who work to promote the reproduction of their queen, or prairie dogs, who call out to warn nearby relatives of danger, at the same time drawing attention to themselves and risking attack.
Recognizing relatives is also helpful for avoiding inbreeding.
Until recently, the ability to recognize kin has been attributed exclusively to animals. But last year, Susan Dudley, at McMaster University in Hamilton, Ontario, reported on the “secret social life” of the American sea rocket, a dune-dwelling plant with little purple flowers, found on the beaches of the Great Lakes.
Dr. Dudley and her graduate student Amanda File found that sea rockets grow more roots when they share a pot with strangers than when they are potted with relatives.
By growing more roots, plants increase their competitive ability underground. Plants with more roots are better at soaking up water and nutrients.
So sea rockets purposely leave more space in the pot for their relatives, giving them a better chance to access water and nutrients. But when a stranger is nearby, they have no inhibitions about hogging all the resources.
Sea rockets seem to recognize their neighbors based on some cue in the roots, since plants potted individually do not change their root-growing behavior when non-relatives are placed in nearby pots.
Since Dr. Dudley published her findings, kin recognition has been demonstrated in several other plant species.
Plants have several different ways of sensing their neighbors. They can detect changes in light, caused by absorption of particular wavelengths by neighboring plants. They can also detect chemicals released by other plants into the soil or air.
One parasitic weed, the dodder, which thrives on nutrients extracted from other plants, actually grows towards its victims, a behavior startlingly similar to hunting.
Plants may be more aware of their surroundings than we’d like to admit. Scientists have known for 100 years that plants send electrical signals from one part of the plant to another. But nobody knows what these signals are for.
Sensory plant biology has blossomed into a hot topic, with a deep rift separating scientists who believe that plants have some sort of sensory-nervous system, and those who maintain that intelligence is limited to animals.
Attributing intelligent or planned behavior to plants may seem a stretch, but maybe plants are smarter than we think. We just haven’t noticed, because they move orders of magnitude slower than we do.
(photo from Harold Davis on flickr.com)