What is Pith?
The pith is the soft, spongy core at the very center of a tree's trunk or branch. In cross-section, it appears as a small, often darker circle right in the middle of the wood.
Structure and Function
Young Trees
- Stores nutrients and water
- Provides structural support in early growth
- May be photosynthetic in green stems
Mature Trees
- Often dries out, shrinks, or becomes hollow
- No longer actively functional
- Heartwood forms around it
Pith Shapes
Different species have characteristic pith shapes in cross-section:
- Round: Most common (e.g., Laurel)
- Star-shaped: Some Fabaceae members
- Triangular: Certain palms
- Hollow: Guarumo and other pioneer species
Costa Rican Examples
Balsa (Ochroma pyramidale)
Very large, soft pith — the entire wood is remarkably lightweight because of its large, thin-walled cells.
Guarumo (Cecropia obtusifolia)
Hollow pith chambers house symbiotic Azteca ants — a classic example of myrmecophytism.
Papaya (Carica papaya)
Almost entirely pith — the trunk is more like a giant herbaceous stem than true wood.
Practical Significance
- Wood quality: Large pith can cause checking (splitting) in lumber.
- Propagation: Pith-rich cuttings root easily but may rot quickly.
- Ecology: Hollow pith provides nesting habitat for insects and small animals.