Acute

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

1. Sharp point: Distinctly pointed (not rounded)
2. Angle 45-90°: Moderate angle at tip
3. Quick convergence: Sides come together fairly rapidly
4. Not drawn out: Point isn't elongated
5. 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

1. Look at leaf tip straight-on
2. Estimate angle where edges meet
3. Less than 45° → Acuminate
4. Between 45-90° → Acute
5. 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