From its diminutive lavender flowers to its straggly windblown stalks, there is nothing about the beach weed known as the Great Lakes sea rocket to suggest that it might be any sort of a botanical wonder.

Yet scientists have found evidence that the sea rocket is able to do something that no other plant has ever been shown to do.

The sea rocket, researchers report, can distinguish between plants that are related to it and those that are not. And not only does this plant recognize its kin, but it also gives them preferential treatment.

If the sea rocket detects unrelated plants growing in the ground with it, the plant aggressively sprouts nutrient-grabbing roots. But if it detects family, it politely restrains itself.

The finding is a surprise, even a bit of a shock, in part because most animals have not even been shown to have the ability to recognize relatives, despite the huge advantages in doing so.

If an individual can identify kin, it can help them, an evolutionarily sensible act because relatives share some genes. The same discriminating organism could likewise ramp up nasty behavior against unrelated individuals with which it is most sensible to be in claws- or perhaps thorns-bared competition.

"I'm just amazed at what we've found," said Susan A. Dudley, an evolutionary plant ecologist at McMaster University in Hamilton, Ontario, who carried out the study with a graduate student, Amanda L. File.

"Plants," Dr. Dudley said, "have a secret social life."

Since the research on sea rockets was published in August in Biology Letters, a journal of the United Kingdom's national academy of science, Dr. Dudley and colleagues have found evidence that three other plant species can also recognize relatives.