Plants Can Recognize and Prefer Their Kin

HAMILTON, ONTARIO, CANADA–The apparently passive garden plant is not as easy-going as people assume, at least not with strangers. Researchers at McMaster University have found that plants become competitive when forced to share a pot with strangers of the same species, but they are more friendly when potted with their siblings.

“The ability to recognize and favor kin is common in animals, but this is the first time it has been shown in plants,” said Dr. Susan Dudley, associate professor of biology at McMaster University in Hamilton.”When plants share their pots, they get competitive and start growing more roots, which allows them to grab water and mineral nutrients before their neighbors get them,” Dudley explains.

Biologist Susan Dudley is the first to discover that plants recognize their kin. “It appears, though, that they only do this when sharing a pot with unrelated plants; when they share a pot with family they don’t increase their root growth,” the biologist says.

Because differences between groups of strangers and groups of siblings only occurred when they shared a pot, the root interactions may provide a cue for kin recognition. Though they lack cognition and memory, Dudley says the study shows plants are capable of complex social behaviors such as altruism towards relatives.

Like humans, says Dudley, the most interesting plant behaviors occur beneath the surface.

Dudley and her student, Amanda File, observed the behavior in sea rocket, Cakile edentula, a member of the mustard family native to beaches throughout North America, including the Great Lakes, where McMaster is located near Lake Ontario.

Sea Rocket
The American sea rocket grows on sandy beaches above the high tide line. The two biologists grew batches of sea rocket in pots of four, either with specimens from the same maternal family or from several different families.Those growing with strangers had a greater mass of roots after two months of growing than those sharing pots with siblings.

Gardeners might want to use this discovery to change their plant arrangements, placing siblings close to one another.

“Gardeners have known for a long time that some pairs of species get along better than others, and scientists are starting to catch up with why that happens,” says Dudley. “What I’ve found is that plants from the same mother may be more compatible with each other than with plants of the same species that had different mothers.

“The more we know about plants, the more complex their interactions seem to be, so it may be as hard to predict the outcome as when you mix different people at a party,” she joked.

How the plants learn which neighbor is a relative is still a mystery. Dudley speculates that a protein or chemical signal specific to each plant’s family might be secreted and detected by other roots nearby.

The study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada. It appeared recently in the Royal Society journal “Biology Letters.”--ENS