Hardly articulate, the tiny strangleweed, a pale parasitic plant, can sense the presence of friends, foes, and food, and make adroit decisions on how to approach them.
Mustard weed, a common plant with a six-week life cycle, can't find its way in the world if its root-tip statolith - a starchy "brain" that communicates with the rest of the plant - is cut off.
The ground-hugging mayapple plans its growth two years into the future, based on computations of weather patterns. And many who visit the redwoods of the Northwest come away awed by the trees' survival for millenniums - a journey that, for some trees, precedes the Parthenon.
As trowel-wielding scientists dig up a trove of new findings, even those skeptical of the evolving paradigm of "plant intelligence" acknowledge that, down to the simplest magnolia or fern, flora have the smarts of the forest. Some scientists say they carefully consider their environment, speculate on the future, conquer territory and enemies, and are often capable of forethought - revelations that could affect everyone from gardeners to philosophers.
Indeed, extraordinary new findings on how plants investigate and respond to their environments are part of a sprouting debate over the nature of intelligence itself.
"The attitude of people is changing quite substantially," says Anthony Trewavas, a plant
biochemist at the University of Edinburgh in Scotland and a prominent scholar of plant intelligence. "The idea of intelligence is going from the very narrow view that it's just human to something that's much more generally found in life."
To be sure, there are no signs of Socratic logic or Shakespearean thought, and the subject of plant "brains" has sparked heated exchanges at botany conferences. Plants, skeptics scoff, surely don't fall in love, bake soufflés, or ponder poetry. And can a simple reaction to one's environment truly qualify as active, intentional reasoning?
But the late Nobel Prize-winning plant geneticist Barbara McClintock called plant cells "thoughtful." Darwin wrote about root-tip "brains." Not only can plants communicate with each other and with insects by coded gas exhalations, scientists say now, they can perform Euclidean geometry calculations through cellular computations and, like a peeved boss, remember the tiniest transgression for months.
To a growing number of biologists, the fact that plants are now known to challenge and exert power over other species is proof of a basic intellect.
"If intelligence is the capacity to acquire and apply knowledge, then, absolutely, plants are intelligent," agrees Leslie Sieburth, a biologist at the University of Utah in Salt Lake City.
For philosophers, one of the key findings is that two cuttings, or clones, taken from the same "mother plant" behave differently even when planted in identical conditions.
"We now know there's an ability of self-recognition in plants, which is highly unusual and quite extraordinary that it's actually there," says Dr. Trewavas. "But why has no one come to grips with it? Because the prevailing view of a plant, even among plant biologists, is that it's a simple organism that grows reproducibly in a flower pot."
But here at the labs on the North Carolina State campus, where fluorescent grow-rooms hold genetic secrets and laser microscopes parse the inner workings of live plants, there is still skepticism about the ability of ordinary houseplants to intellectualize their environment.
Most plant biologists are still looking at the mysteries of "signal transduction," or how genetic, chemical, and hormonal orders are dispersed for complex plant behavior. But skeptics say it's less a product of intelligence than mechanical directives, more genetic than genius. Some see the attribution of intelligence to plants as relative - an oversimplification of a complex human trait.
And despite intensifying research, exactly how a plant's complex orders are formulated and carried out remains draped in leafy mystery.
"There is still much that we do not know about how plants work, but a big part of intelligence is self-consciousness, and plants do not have that," says Heike Winter Sederoff, a plant biologist at N.C. State.
Still, a new NASA grant awarded to the university to study gravitational effects on crop plants came in part due to new findings that plants have neurotransmitters very similar to humans' - capable, perhaps, of offering clues on how gravity affects more sentient beings. The National Science Foundation has awarded a $5 million research grant to pinpoint the molecular clockwork by which plants know when to grow and when to flower.
The new field of plant neurobiology holds its first conference - The First Symposium on Plant Neurobiology - in May in Florence, Italy.
The debate is rapidly moving past the theoretical. In space, "smart plants" can provide not only food, oxygen, and clean air, but also valuable companionship for lonely space travelers, say some - a boon for astronauts if America is to go to Mars. Research on the workings of the mustard weed's statolith, for example, may one day yield a corn crop with 1-3/8 the gravitational force of Earth.
Some Earth-bound farmers, meanwhile, see the possibility of communicating with plants to time waterings for ultimate growth. A new gene, Bypass-1, found by University of Utah researchers, may make that possible.
Still, it can be hard for the common houseplant to command respect - even among those who study it most closely.
"When I was a postdoc, I had a neighbor who watched me buy plants, forget to water them, and throw them out, buy them and throw them out," says Dr. Sieburth. "When she found out I had a PhD in botany, I thought she was going to die."