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
- Pollination: Pollen lands on stigma
- Germination: Pollen grain sprouts pollen tube
- Growth: Tube grows down through style
- Fertilization: Sperm cells reach ovules in ovary
- Seed development: Ovules become seeds
- 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:
- Locate in flower center
- Count stigma lobes (= carpels)
- Check if sticky (touch gently)
- Note length of style
- Feel for ovary at base
- Compare to stamen number
Best time to observe:
- Flower just opened
- Before pollination
- Stigma fresh and receptive