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.

Some scientists say plants 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, 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."

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. Plants have neurotransmitters very similar to humans' - capable, perhaps, of offering clues on how gravity affects more sentient beings.

Excerpt from Christian Science Monitor, www.csmonitor.com