By Jennifer Langille
The answer is phototropism.
Let’s break down the word: photo is Greek for “light,” and tropism simply means “turn”. So, phototropism literally means a plant’s movement or turning towards the light. It’s one of the ways plants interact with their environment—slowly, silently, and often beautifully.
Here are five fun facts to help you appreciate this and other botanical magic:
1. It’s all about growth hormones.
Phototropism is triggered by special plant hormones called auxins. These hormones help regulate growth, and they’re always on the move—literally. When light hits one side of a stem, auxins migrate to the shaded side. There, they stimulate the cells to elongate more than the cells on the sunny side.
That uneven growth causes the stem to bend toward the light. Auxins are at work all over the plant, but in phototropism, they act like little messengers telling the plant, “This way to the sun!” You’ve probably also seen this in seedlings on a windowsill that lean towards the light.
- Gravitropism (Geotropism): Knowing up from down
Even seeds planted sideways somehow grow the “right” way: roots downward, shoots upward. That’s thanks to gravitropism, the plant’s response to gravity. Roots grow with gravity (positive gravitropism), while stems push against it (negative gravitropism). It’s why buried seeds don’t stay confused for long.
- Heliotropism: Chasing the sun
Heliotropism is a bit different from phototropism. Rather than growing permanently toward the light, some plants move their leaves or flower heads throughout the day to follow the sun’s path. Young sunflowers are famous for this. They track the sun from east to west, then reset overnight. It’s a temporary movement, but a charming one.
- Thigmotropism: Responding to touch
Ever watched a clematis vine curl its way around a trellis? That’s thigmotropism—a plant’s growth response to touch (thigma is Greek for “touch”). Tendrils and climbing stems use this ability to sense nearby structures and anchor themselves. The movement may be slow, but it’s remarkably precise, purposeful, and often essential for the plant’s survival.
Here’s a curious twist: in the Northern Hemisphere, most twining vines spiral counterclockwise, while in the Southern Hemisphere, they tend to twirl clockwise.
Scientists are still puzzling out why, but it’s a quiet reminder that plants respond not only to what’s close by, but also to the broader forces that shape their world. Listen to this wonderfully silly song about plants that twist and twirl!
June 2025
2 Responses
Another fantastic article! I didn’t know there were so many “ tropisms”. If it was anyone but you I would think you made up “ thigmotropism”.
I’ve seen all of these in my plants. The poor things are so abused and neglected.
Chris and I were telling Martha and Sean last night about our day at the Tatamagouche Market and our visit to your beautiful home and gardens.
Thank you, Pat. Tropisms, indeed! Isn’t this fascinating, that plants have this ability? It amazes me. I was so happy you & Chris came to see me, and really enjoyed our visit!