What is Dimorphism?
Dimorphism means having two different forms. In trees, this can appear as different leaf shapes on the same individual (heterophylly), different forms between juvenile and adult trees, or visible differences between male and female trees.
Types of Dimorphism in Trees
Leaf Dimorphism (Heterophylly)
- Juvenile leaves may be very different from adult leaves.
- Sun leaves (upper canopy) are often smaller, thicker, and more lobed than shade leaves (understory).
- This can complicate identification — juvenile trees may look like a completely different species.
Sexual Dimorphism
- In dioecious species (separate male and female trees), male and female trees may differ in:
- Size: Females sometimes shorter due to reproductive energy investment.
- Crown shape: Different branching patterns.
- Phenology: Different flowering and leafing times.
Developmental Dimorphism
- Young trees may have spiny trunks that become smooth with age (e.g., Ceiba).
- Bark texture, branching pattern, and growth form can change dramatically with maturity.
Costa Rican Examples
Ceiba (Ceiba pentandra)
Young trees have heavily spined trunks; mature trees lose their spines and develop massive buttress roots — a dramatic developmental dimorphism.
Guarumo (Cecropia obtusifolia)
Juvenile leaves are entire (unlobed); adult leaves are deeply palmate with 7–11 lobes.
Why It Matters
- Identification: Knowing about dimorphism prevents misidentifying juvenile or shade-form trees.
- Ecology: Different leaf forms optimize photosynthesis under different light conditions.
- Forestry: Understanding developmental dimorphism helps assess tree maturity and health.