What Is a Decussate Leaf Arrangement? Pairs at Right Angles
A decussate leaf arrangement has leaves in opposite pairs, with each pair turned 90 degrees from the pair below. The University of Illinois woody plants tutorial defines decussate as leaves in opposite pairs that rotate 90 degrees at every node.
The short answer
Decussate is a kind of opposite arrangement. NC State Extension notes opposite leaves occur when two leaves at each node sit across from one another. The University of Illinois notes decussate pairs turn 90 degrees at every node. Distichous pairs line up in two ranks.
What does decussate mean?
The University of Illinois tutorial notes decussate leaves are arranged in opposite pairs that rotate 90 degrees at every node. From above, the pairs form a cross.
How is decussate different from opposite?
Opposite means two leaves per node. Decussate describes how the pairs turn along the stem.
| Arrangement | Leaves per node | Source |
|---|---|---|
| Alternate | One | NC State |
| Opposite | Two across from each other | NC State |
| Decussate | Two, turning 90 degrees each node | Illinois |
| Distichous | Two, in two ranks | Illinois |
| Whorled | Three or more | NC State |
Source: NC State Extension plus University of Illinois.
Which plants have decussate leaves?
The University of Illinois lists corneliancherry dogwood plus hedge maple among opposite leaved plants. NC State notes flowering dogwood leaves are opposite, while Colorado State lists maple for opposite plus catalpa for whorled. The University of Illinois notes arrangement is not always decussate or distichous, so check several nodes.
How to: step by step
- Pick a stem with opposite leaves.
- Sight down from the tip.
- Find the top leaf pair.
- Check the pair below it.
- See if it turns 90 degrees.
- Repeat on a few nodes.
Troubleshooting
Pairs line up: a distichous stem. The University of Illinois notes this pattern.
One leaf per node: alternate leaves. NC State notes this arrangement.
Three leaves at a node: a whorl. NC State notes whorls need three or more.
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
- Extension Gardener Handbook, chapter 3: botany, NC State Extension
- Cornus florida (flowering dogwood), NC State Extension Gardener Plant Toolbox
- Botany (CMG GardenNotes 120), Colorado State University Extension
- Opposite leaf arrangement, University of Illinois woody plants tutorial
FAQ
Are all opposite leaves decussate?
No. The University of Illinois tutorial notes opposite leaves may be distichous or decussate.
Does flowering dogwood have opposite leaves?
Yes. NC State Extension notes flowering dogwood leaves are opposite with veins that arch toward the tip.
What is a distichous arrangement?
The University of Illinois tutorial notes distichous leaves are arranged in two ranks along either side of the stem.
Is decussate the same as whorled?
No. NC State Extension notes a whorl has three or more leaves at a node, while decussate pairs have two.
What is an alternate arrangement?
NC State Extension notes alternate leaves have one leaf at each node, alternating on each side of the stem.
