What Is an Ocrea? Sheaths at the Nodes of Knotweeds
An ocrea is a sheath like structure that wraps the stem where a leaf meets it. NC State Extension notes Japanese knotweed has an ocrea at this joint, plus mile a minute has rounded leaf like stipules called ocrea at its nodes.
The short answer
An ocrea is a sheath at the node. NC State Extension notes that where Japanese knotweed leaves meet the stem there is a sheath like structure called an ocrea. On mile a minute the stems are jointed at the nodes with rounded leaf like stipules called ocrea. Look at the leaf joint.
Where is the ocrea on a plant?
It lies at the node. NC State Extension notes the node is the stem area where leaves are, or once were, attached, plus a bud sits within it. The ocrea wraps the stem where the leaf joins.
Which plants have an ocrea?
NC State lists it for Japanese knotweed plus mile a minute, two members of the knotweed family.
| Plant | Ocrea detail | Source |
|---|---|---|
| Japanese knotweed | Sheath where leaves meet the stem | NC State |
| Mile a minute | Rounded leaf like stipules at nodes | NC State |
Source: NC State Extension Gardener Plant Toolbox.
Why does the ocrea matter for ID?
It offers a clue at the node. NC State notes Japanese knotweed has hollow stems with swollen nodes that look like bamboo, though it is not related to bamboo. The ocrea at each joint helps confirm the knotweed family.
How to: step by step
- Find a leaf on the stem.
- Follow its stalk to the stem.
- Inspect the joint.
- Check for a wrapping sheath.
- Note how the node is swollen.
- Compare with the table above.
Troubleshooting
No sheath: check a newer node. NC State notes leaves may once have been attached at older nodes.
Stem looks like bamboo: Japanese knotweed. NC State notes its swollen nodes.
Round leaf like parts: mile a minute. NC State notes its ocrea look like stipules.
For stem 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
- Reynoutria japonica (Japanese knotweed), NC State Extension Gardener Plant Toolbox
- Persicaria perfoliata (mile a minute), NC State Extension Gardener Plant Toolbox
- Rheum rhabarbarum (rhubarb), NC State Extension Gardener Plant Toolbox
- Extension Gardener Handbook, chapter 3: botany, NC State Extension
FAQ
What is a node?
NC State Extension notes the node is the stem area where leaves are attached, or once were, plus a bud sits within it.
Is the ocrea part of the leaf?
It sits at the leaf joint. NC State Extension notes the sheath like ocrea is where Japanese knotweed leaves meet the stem.
What is an internode?
NC State Extension notes the area between nodes is the internode.
Is an ocrea the same as a stipule?
NC State Extension describes mile a minute ocrea as rounded leaf like stipules at the nodes.
Why do knotweed stems look like bamboo?
NC State Extension notes Japanese knotweed has hollow stems with swollen nodes, though it is not related to bamboo.
