Flower Anatomy: Sepals, Petals, Stamens, and Pistils
Flower Anatomy
First, there is a stalk (pedicel) which supports the flower. Some flowers may be without a stalk (sessile). The tip of the stalk may also be enlarged to form a cup-shaped receptacle or thalamus.
A flower is a specialized shoot in which the leaves are modified into floral structures.
The floral parts are borne on the thalamus in four whorls:
- First Whorl: Green sepals (collectively called calyx)
- Second Whorl: Large, brightly-colored petals (collectively called corolla).
- Third Whorl: Male parts (♂)
- Fourth Whorl: Centrally located pistil that may be formed of a single female unit called carpel, or of several fused carpels (collectively called gynoecium). Each carpel consists of a basal ovary, a middle style, and the uppermost stigma.
Complete and Incomplete Flowers
A complete (or perfect) flower is one that contains all four floral whorls.
If one or more sets of floral whorls are missing, the flower is called incomplete (or imperfect).
The essential parts of a flower are those that are directly concerned with reproduction.
These parts consist of the stamens (male parts) and the carpels (female parts).
The non-essential (accessory) parts are simply the helping parts which either protect the reproductive part of the flower or make the flower attractive for pollination.
Bracts
When a flower arises in the axil of a leaf-like structure, this structure is known as a bract.
Bracts may be green like ordinary leaves, or at times they are colored.
The large and colorful bract of a Bougainvillea is easily mistaken for a petal.
The actual flower in this case is small, somewhat cylindrical, and attached on the inner side of the bract.
Nectaries
Most flowers produce a sweet, fragrant liquid called nectar.
Groups of nectar-secreting cells are called nectaries.
Location: Situated usually at the base of the pistil or at the bases of the petals.
Example: Nasturtium
Sepals
The sepals may be free (polysepalous) or fused (gamosepalous).
Sepals are usually green, but in some cases, they are brightly colored (called petaloid sepals).
Example: Gul Mohar (where they are red)
- The sepals protect the young flower bud.
- When green, they also perform photosynthesis.
Corolla
Petals may be free (polypetalous) or united (gamopetalous), forming a tube.
- Attract insects for pollination.
- Protect stamens and pistils.
Monadelphous: Stamens are united in one group by their filaments. Only anthers are free. Example: China rose, cotton.
Diadelphous (two): The filaments are united in two bundles. Example: Pea
Polyadelphous (several): The filaments are united in several groups. Example: Bombax
Gynoecium
Gynoecium is also known as the pistil.
It is composed of one or more carpels.
Each carpel consists of three parts: stigma, style, and ovary.
Stigma: The terminal knob-like part.
Function: It serves as the landing place for pollen during pollination.
Style: The tubular, slender stalk which connects the stigma to the ovary.
Function: Connects the stigma to the ovary.
Ovary: The swollen basal portion composed of one or many carpels fused together.
Inflorescence and Placentation
Inflorescence: The mode of arrangement of flowers on the axis of a plant.
Placenta: The tissue that attaches the ovule to the wall of the ovary.