Pistil: Female Reproductive Structure of a Flower – Anatomy & Function
The pistil (or carpel, if single) is the female reproductive organ of a flowering plant (angiosperm). It receives pollen, facilitates fertilization, and develops into fruit/seed.
Anatomy (Basal to Apical)
| Part | Description | Function |
|---|
| Ovary | Swollen basal portion; contains one or more ovules (each with an embryo sac/egg cell) | Site of fertilization; matures into fruit |
| Style | Slender stalk connecting ovary to stigma; may be short, long, or absent (sessile stigma) | Pathway for pollen tube growth; site of pollen-pistil recognition (self-incompatibility) |
| Stigma | Apical receptive surface; often sticky, feathery, or papillate | Captures pollen; hydrates & germinates it; selects compatible pollen |
Pistil vs. Carpel
- Carpel: A single ovule-bearing unit (one ovary + style + stigma).
- Pistil: One or fused carpels (syncarpous) — e.g., tomato (2 fused), lily (3 fused). Apocarpous = separate carpels (e.g., strawberry, buttercup).
Fertilization Sequence
- Pollen lands on stigma → hydrates → germinates pollen tube.
- Tube grows down style (guided by chemotropic signals from ovule).
- Enters ovule via micropyle → releases two sperm cells.
- Double fertilization: (1) Sperm + egg → zygote (2n) → embryo. (2) Sperm + 2 polar nuclei → triploid (3n) endosperm (nutritive tissue).
- Ovule → seed; Ovary → fruit.
Diversity
- Simple pistil: 1 carpel (pea, bean).
- Compound pistil: 2+ fused carpels (most flowering plants).
- Stigma types: Wet (sticky exudate) vs. dry (papillae); specialized for wind (feathery) or insect (compact) pollination.
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