Pistil

What is a Pistil?

The pistil is the female part of a flower - where seeds develop after pollination. It has three main parts: a sticky tip (stigma) that catches pollen, a stalk (style) connecting the parts, and a swollen base (ovary) containing ovules that become seeds.

Structure

Three Main Parts

Stigma:

• Pollen-receptive surface at top
• Often sticky or hairy
• May be lobed or feathery
• Receives pollen grains

Style:

• Stalk between stigma and ovary
• Pollen tubes grow through it
• Can be long or short, or absent
• One or multiple per flower

Ovary:

• Swollen base containing ovules
• Ovules become seeds after fertilization
• Ovary becomes fruit
• Contains one to many ovules

Types of Pistils

Simple Pistil (One Carpel)

Single unit:

• One ovary, style, stigma
• From one carpel
• Example: Pea, avocado

Compound Pistil (Multiple Carpels)

Fused carpels:

• Appears as one pistil
• Multiple carpels joined
• Most common type
• Example: Tomato, mango

Multiple Pistils

Separate carpels:

• Many individual pistils per flower
• Each makes its own fruit
• Example: Magnolia, blackberry

Position in Flower

Superior Ovary

Above other parts:

• Ovary at top of receptacle
• Stamens below ovary
• Becomes fruit with withered flower parts at base
• Example: Guanacaste, most legumes

Inferior Ovary

Below other parts:

• Ovary embedded in receptacle
• Flower parts appear above ovary
• Becomes fruit with flower remnants on top
• Example: Mango, guava, apple

Function

Reproduction Process

1. Pollination: Pollen lands on stigma
2. Germination: Pollen grain sprouts pollen tube
3. Growth: Tube grows down through style
4. Fertilization: Sperm cells reach ovules in ovary
5. Seed development: Ovules become seeds
6. Fruit development: Ovary grows into fruit

Costa Rican Examples

Aguacate/Avocado (Persea americana)

• Simple pistil (one carpel)
• Becomes drupe fruit
• Large single seed
• Perfect flowers (both stamens and pistils)

Mango (Mangifera indica)

• Compound pistil
• Inferior ovary
• One fertile carpel (4 others sterile)
• Drupe with large flat seed

Ceiba (Ceiba pentandra)

• Compound pistil
• 5 carpels
• Long style projecting beyond stamens
• Becomes large capsule fruit

Stigma Variations

Types by Pollen Mode

Dry stigma:

• Wind-pollinated trees
• Non-sticky surface
• Feathery or branched
• Catches airborne pollen

Wet stigma:

• Insect/bird pollinated
• Sticky secretion
• Traps pollen grains
• Most Costa Rican trees

Style Length

Functional Adaptations

Long styles:

• Stigma extends beyond stamens
• Prevents self-pollination
• Accessed by long-tongued pollinators
• Example: Many trumpet flowers

Short or no style:

• Stigma near ovary
• Direct path for pollen tubes
• Quick fertilization
• Example: Some wind-pollinated trees

Carpel Number and Fruit Type

| Carpels | Example Tree | Fruit Type | | ------- | ------------ | ---------- | | 1 | Avocado | Drupe | | 2 | Jacaranda | Capsule | | 3 | Palms | Drupe | | 5 | Ceiba | Capsule | | Many | Magnolia | Aggregate |

Ovule Development

Before Fertilization

Ovules in ovary:

• Contain female gamete (egg)
• Awaiting fertilization
• Multiple per ovary
• Not all may be fertilized

After Fertilization

Seeds develop:

• Fertilized ovules become seeds
• Unfertilized ovules abort
• Seed contains embryo
• Protected by seed coat

Identifying Features

Family Characteristics

Fabaceae (legumes):

• Single carpel
• Superior ovary
• Becomes pod (legume)

Malvaceae (hibiscus family):

• 5 carpels
• Compound pistil
• Style branches into 5 stigmas

Anacardiaceae (mango family):

• Usually 1-3 carpels
• Often only one fertile
• Drupes

Economic Importance

Fruit Production

All fruits come from pistils:

• Ovary develops into fruit
• Seeds inside from ovules
• Crucial for food production
• Pollination essential

Why It Matters

Understanding pistils helps with:

• Flower identification: Number and arrangement diagnostic
• Pollination: Knowing fertilization requirements
• Fruit prediction: Ovary type indicates fruit type
• Breeding: Controlled crosses for hybrids
• Yield: Pistil health affects seed/fruit production

Field Tips

Examining pistils:

1. Locate in flower center
2. Count stigma lobes (= carpels)
3. Check if sticky (touch gently)
4. Note length of style
5. Feel for ovary at base
6. Compare to stamen number

Best time to observe:

• Flower just opened
• Before pollination
• Stigma fresh and receptive