What Is a Pulvinus? The Joint That Lets Leaves Move
A pulvinus is a swelling on a leaf stalk that lets the leaf move. UF/IFAS Extension notes cocoa leaves have a long petiole with a swelling at each end called a pulvinus, plus the pulvinus lets the leaf swivel to catch sunlight.
The short answer
A pulvinus is a swollen joint on the petiole. UF/IFAS Extension notes cocoa has one at each end of the leaf stalk, plus it lets the leaf swivel toward sunlight. NC State Extension notes purple shamrock leaves close up at night or when disturbed, a leaf movement gardeners can see.
What does a pulvinus do?
It lets a leaf shift position. UF/IFAS notes the pulvinus allows the cocoa leaf to swivel to catch sunlight. Colorado State University Extension notes the petiole is the leaf stalk, so the pulvinus is a swelling there.
Where is a pulvinus found?
On cocoa, UF/IFAS notes it sits at each end of the petiole. Colorado State notes compound leaves have several leaflets arising from the same petiole.
| Plant | Leaf detail | Source |
|---|---|---|
| Cocoa | Pulvinus at each end of the petiole | UF/IFAS |
| Purple shamrock | Leaves close at night | NC State |
| Purple shamrock | Flowers close at night | NC State |
Source: UF/IFAS Extension plus NC State Extension.
Which plants show leaf movement?
NC State notes Oxalis triangularis leaves close up at night or when disturbed, plus its flowers also close at night. UF/IFAS notes cocoa leaves swivel to catch sunlight. NC State notes guard cells usually close the stomata in darkness, a separate change at the leaf surface.
How to: step by step
- Pick a plant with moving leaves.
- Find the leaf stalk.
- Check each end of it.
- Check for a swollen joint.
- Watch the leaf in low light.
- Note how it changes position.
Troubleshooting
No swelling seen: use a hand lens. UF/IFAS notes it sits at the stalk ends.
Leaves closed by day: the plant was disturbed. NC State notes purple shamrock closes when disturbed.
Flowers shut too: nighttime. NC State notes its flowers close at night.
For leaf parts see cannabis leaf anatomy plus cannabis nodes and internodes. Read companion plants when growing marijuana plus growing cannabis near trees. Kind Seed Co also stocks cannabis seeds.
Sources
- Oxalis triangularis (purple shamrock), NC State Extension Gardener Plant Toolbox
- Extension Gardener Handbook, chapter 3: botany, NC State Extension
- Botany (CMG GardenNotes 120), Colorado State University Extension
- Cocoa (chocolate bean) growing in the Florida home landscape, UF/IFAS Extension
FAQ
Do oxalis leaves close at night?
Yes. NC State Extension notes Oxalis triangularis leaves close up at night or when disturbed.
Where is the pulvinus on cocoa?
UF/IFAS Extension notes cocoa has a long petiole with a swelling at each end called a pulvinus.
What is a petiole?
Colorado State University Extension notes the petiole is the leaf stalk.
What is a leaflet?
Colorado State University Extension notes a compound leaf has several leaflets arising from the same petiole.
Do oxalis flowers close too?
Yes. NC State Extension notes the white to pink flowers of Oxalis triangularis also close at night.
