How, exactly, do plants move?

Trout lilies fling their petals back every morning to open the pollen shop. Photo by Sherry McPhail.

It’s true that we don’t think too much about this mystery until we start to wonder how some flowers close every night, like trout lilies and dandelions. Or how carnivorous plants shut their traps fast enough to catch a bug.

Plants are actually pretty mobile––just usually on a different time scale from us. Watch BBC’s Green Planet or a spring flowers time lapse by Neil Bromhall to speed things up.

So how do plants move? There are two main types of plant movement, both kinds in response to things like light, temperature, touch, water, wind and gravity.

Tropic plant movement is the slow movement of plants growing, cell by cell. Tropic movement is directional: a plant’s growth hormone tells cells to multiply toward sunlight, or away from wind, or down into the ground towards gravitational pull, or any other good reason to go one way or another.

The other kind, Nastic movement, doesn't involve cell growth, so it’s great for getting things done quickly. Here’s how it works: some trigger, like the touch of a bug in the trap or a cold nighttime temperature, starts fluid moving from some cells to other cells. It’s non-directional movement––not towards or away from the bug or the chill––and reversible, usually open/close.

Here’s an example: Venus flytraps can close quickly because, in response to a bug touching their trigger hairs, super-expandable cells in the trap’s outer walls swell quickly with water from cells from the inner walls, closing the hinge in a tenth of a second. Bugs worth digesting don’t stand a chance.

After the plant digests its prey, the trap’s outer wall cells transfer fluid back to the inner wall cells, reopening the trap for tomorrow’s hunt. Read more about how the plant counts, and remembers!

So now we all know how plants move, more or less. Fascinating, yes?