Flower Structure:

• A flower is the reproductive structure of angiosperms (flowering plants).
• It typically consists of four main whorls or parts arranged in concentric circles.

Whorls of a Flower:

• Flowers have four primary whorls:

a)  Calyx: The outermost whorl, composed of sepals.

b)  Corolla: The second whorl, consisting of petals.

c)  Androecium: The third whorl, containing stamens.

d)  Gynoecium: The innermost whorl, comprising carpels or pistils.

Reproductive Organs:

• The reproductive organs of a flower are the androecium (male) and gynoecium (female).
• Androecium: Contains stamens, each consisting of anther and filament, producing pollen.
• Gynoecium: Contains carpels, each consisting of stigma, style, and ovary, where ovules are located.

Parts of a Flower:

• Sepals: Green, leaf-like structures in the calyx that protect the flower bud.
• Petals: Usually colorful and attractive; they make up the corolla and serve to attract pollinators.
• Stamens: Male reproductive organs consisting of anther (producing pollen) and filament.
• Carpel/Pistil: Female reproductive organ containing stigma (receptive surface), style (connects stigma to ovary), and ovary (houses ovules).
• Ovules: Structures within the ovary that contain the female gametes (eggs).

Aestivation:

• Aestivation refers to the arrangement of sepals or petals in a floral bud before they open.

• Common aestivation patterns include:

  a) Valvate: Overlapping but not touching.

  b) Twisted (Contorted): Overlapping with one margin inside the other.

  c) Imbricate: Overlapping, with one sepal or petal covering the other partially.

  d) Vexillary (Papilionaceous): In pea flowers, with one large petal (banner) outside, two lateral petals (wings), and two smaller fused petals (keel) inside.

  e) Quincuncial: When sepals or petals are arranged in a whorl of five, with two partially overlapping outer elements and three inner elements.