What is Acute?
An acute apex is a leaf tip that forms a sharp point with an angle between 45-90 degrees. Not as drawn-out as acuminate, but sharper than obtuse. Think of a moderate point—distinctly sharp but not elongated.
Identifying Acute Apexes
Key Features
- Sharp point: Distinctly pointed (not rounded)
- Angle 45-90°: Moderate angle at tip
- Quick convergence: Sides come together fairly rapidly
- Not drawn out: Point isn't elongated
- Common form: Very frequent in tropical trees
Comparison with Similar Apexes
Apex Types by Angle
Acuminate: <45° (very sharp, drawn-out point) Acute: 45-90° (sharp point, moderate angle) Obtuse: >90° (blunt, rounded point) Rounded: No point, smoothly curved
Visual Measurement
The Angle Test
- Look at leaf tip straight-on
- Estimate angle where edges meet
- Less than 45° → Acuminate
- Between 45-90° → Acute
- More than 90° → Obtuse
Use a protractor for precision, or estimate with folded paper (45° = perfect diagonal, 90° = right angle).
Costa Rican Examples
Guanacaste (Enterolobium cyclocarpum):
- Leaflets with acute apexes
- Bipinnate leaves
- National tree
Laurel (Cordia alliodora):
- Acute to acuminate apex
- Important timber species
- Variable tip form
Many Mango (Mangifera indica):
- Acute apex common
- Lanceolate leaves
- Fruit tree
Jobo (Spondias mombin):
- Leaflets acute-tipped
- Pinnate compound leaves
- Native fruiting tree
Why Acute Matters
Identification Value
Species diagnostic:
- Acute vs acuminate can separate species
- Some species consistently acute
- Family patterns exist
Quick field check:
- Easy to assess visually
- No microscope needed
- Useful sorting character
Common Mistakes
Don't confuse:
- Acute with acuminate (check if angle <45° or drawn out)
- Acute with obtuse (check if angle >90°)
- Juvenile with mature leaves (apex can change)
- Damaged tip with natural form
Remember:
- Acute = 45-90° angle
- Check multiple leaves on same tree
- Look at healthy, undamaged tips
- Use reference examples
Field Recording
Notation
Precise:
- "Apex acute" (45-90° angle)
- "Apex shortly acute" (closer to 90°)
- "Apex acute to acuminate" (variable, 30-75°)
Complete description: "Leaves simple, elliptic, 8-12 cm long, margins entire, apex acute, base cuneate, glabrous on both surfaces."
Why It Matters
Understanding acute apexes helps with:
- Tree identification: Diagnostic feature
- Species comparison: Distinguishing similar species
- Age assessment: Apex form can vary with maturity
- Botanical accuracy: Precise terminology
- Field guide use: Standard descriptive language