What is Obtuse?
An obtuse apex is a blunt or rounded leaf tip with an angle greater than 90 degrees. It's not sharply pointed like acute or acuminate—think of it as a gently rounded or blunt end.
Identifying Obtuse Apexes
Key Features
- Blunt tip: Not sharply pointed
- Angle >90°: Broad angle at apex
- Slow convergence: Sides come together gradually or barely
- Rounded appearance: May grade into "rounded" apex
- Not abrupt: Smooth transition to tip
Comparison with Similar Apexes
Apex Types by Angle
Acuminate: <45° (very sharp, prolonged point) Acute: 45-90° (sharp point, moderate angle) Obtuse: >90° (blunt point, broad angle) Rounded: No angle, completely curved Truncate: Cut straight across (no point)
Visual Identification
The Angle Test
- Look at leaf tip
- Estimate angle where edges meet
- More than 90° but still pointed → Obtuse
- Completely rounded (no angle) → Rounded
- Cut straight across → Truncate
Remember: 90° = right angle (like corner of square). Obtuse is wider/blunter than right angle.
Costa Rican Examples
Coco (Cocos nucifera):
- Palm leaflets often obtuse-tipped
- Broad, blunt apex
- Beach palm
Níspero (Manilkara zapota):
- Leaves often obtuse to rounded
- Thick, leathery
- Sapodilla fruit tree
Some Ficus species:
- Variable apex forms
- Some have obtuse tips
- Depends on species and conditions
Why Obtuse Tips?
Functional Advantages
Reduced mechanical stress:
- Blunt tips less prone to tearing
- Wind damage reduction
- Important in exposed sites
Water conservation:
- Less surface area at tip
- Reduced transpiration
- Common in dry climates
Protection:
- Rounded tips less attractive to herbivores
- No vulnerable sharp point
- Damage-resistant
Ecological Context
Where obtuse is common:
- Dry forest species
- Wind-exposed sites
- Beach/coastal trees
- Thick, leathery leaves
Less common in:
- Rainforest understory (prefer acuminate drip tips)
- Pioneer species (often acute)
- Temperate zones
Common Mistakes
Don't confuse:
- Obtuse with rounded (obtuse still has slight point)
- Obtuse with acute (check angle - obtuse >90°)
- Obtuse with truncate (truncate is straight across)
- Damaged tip with natural obtuse form
Remember:
- Obtuse = blunt but still pointed
- Angle wider than 90° (right angle)
- Check multiple leaves on same tree
- Use protractor or folded paper for precision
Field Recording
Notation
Precise:
- "Apex obtuse" (>90° angle)
- "Apex obtuse to rounded" (variable, 90-180°)
- "Apex broadly obtuse" (very blunt, approaching rounded)
Complete description: "Leaves simple, oblong, 8-12 cm long, margins entire, apex obtuse, base cuneate, glabrous on both surfaces, thick and leathery."
Why It Matters
Understanding obtuse apexes helps with:
- Tree identification: Diagnostic feature
- Species comparison: Distinguishing similar species
- Ecological adaptation: Understanding environmental pressures
- Botanical accuracy: Precise terminology
- Field guide use: Standard descriptive language