Question
What are the four whorls of a flower — calyx, corolla, androecium, and gynoecium — and what is the function of each?
Solution — Step by Step
A typical flower has four whorls arranged in concentric circles on the thalamus (receptacle):
- Calyx (outermost) — made of sepals
- Corolla — made of petals
- Androecium — male reproductive whorl (stamens)
- Gynoecium (innermost) — female reproductive whorl (carpels/pistil)
The outer two (calyx + corolla) are accessory whorls — they help but are not directly reproductive. The inner two (androecium + gynoecium) are essential whorls — they carry out reproduction.
Made of sepals (usually green, leaf-like).
Function: Protects the flower bud before it opens. In some plants (like Hibiscus), there is an additional outer whorl called the epicalyx.
- Gamosepalous: sepals fused (e.g., Hibiscus)
- Polysepalous: sepals free (e.g., Mustard)
After flowering, the calyx may fall off or persist. In brinjal and tomato, the calyx persists even in the fruit.
Made of petals (usually brightly coloured).
Function: Attracts pollinators (insects, birds) through colour, scent, and sometimes nectar guides.
- Gamopetalous: petals fused (e.g., Datura, Petunia)
- Polypetalous: petals free (e.g., Rose, Mustard)
Different petal arrangements create different symmetries:
- Actinomorphic: radial symmetry (can be divided equally in any plane) — e.g., Mustard
- Zygomorphic: bilateral symmetry (one plane only) — e.g., Pea, Bean
Made of stamens, each consisting of:
- Filament: the stalk
- Anther: the swollen top part that produces pollen grains (male gametes)
A stamen with a sterile anther is called a staminode.
Types based on fusion:
- Free stamens: polyandrous
- Fused into one bundle: monadelphous (e.g., Hibiscus)
- Two bundles: diadelphous (e.g., Pea — 9 fused + 1 free)
Made of one or more carpels (also called pistils). Each carpel has three parts:
- Stigma: sticky tip that receives pollen
- Style: the tube connecting stigma to ovary
- Ovary: swollen base containing ovules (which develop into seeds after fertilization)
Types based on carpel fusion:
- Apocarpous: carpels free (e.g., Lotus, Rose)
- Syncarpous: carpels fused (e.g., Mustard, Tomato)
flowchart TD
A["Flower Structure"] --> B["Accessory Whorls"]
A --> C["Essential Whorls"]
B --> D["Calyx: Sepals — Protection"]
B --> E["Corolla: Petals — Attraction"]
C --> F["Androecium: Stamens — Male, pollen production"]
C --> G["Gynoecium: Carpels — Female, ovule bearing"]
F --> H["Anther + Filament"]
G --> I["Stigma + Style + Ovary"]Why This Works
The four-whorl arrangement is a highly efficient reproductive strategy. The outer whorls protect and advertise, while the inner whorls carry out the actual business of reproduction. This layered design ensures that the delicate reproductive organs (stamens and carpels) are protected during development and exposed only when the flower opens for pollination.
Flowers that have all four whorls are called complete flowers. Those missing any whorl are incomplete. If both androecium and gynoecium are present, the flower is bisexual (perfect). If only one is present, it is unisexual (imperfect).
Alternative Method
For NEET-level identification, remember the floral formula format. For example, Solanaceae (tomato family): it encodes the number and fusion status of each whorl in one compact notation. Learning floral formulas for the 6 NEET-important families (Fabaceae, Solanaceae, Liliaceae, Brassicaceae, Asteraceae, Poaceae) covers most exam questions.
Common Mistake
Students confuse carpel with pistil. In a syncarpous gynoecium (fused carpels), the entire fused structure is called a pistil — but it is made of multiple carpels. In an apocarpous gynoecium, each carpel is itself a pistil. So “one pistil” does not always mean “one carpel.” NEET 2023 had a question that required distinguishing these terms correctly.