Obtuse

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

1. Blunt tip: Not sharply pointed
2. Angle >90°: Broad angle at apex
3. Slow convergence: Sides come together gradually or barely
4. Rounded appearance: May grade into "rounded" apex
5. 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

1. Look at leaf tip
2. Estimate angle where edges meet
3. More than 90° but still pointed → Obtuse
4. Completely rounded (no angle) → Rounded
5. 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