Biology: Flower Structure and Symmetry

Flower Structure

• Typical flowers feature four whorls: calyx, corolla, androecium, and gynoecium.
• Calyx and corolla are accessory organs; androecium and gynoecium are reproductive organs.

Flower Types

• Bisexual Flowers: Contain both androecium and gynoecium.
• Unisexual Flowers: Contain either androecium or gynoecium.

Symmetry Types

• Actinomorphic (Radial Symmetry): Can be divided into two equal halves through any plane.
• Zygomorphic (Bilateral Symmetry): Divided into two halves through one specific plane.
• Asymmetrical: Cannot be divided into equal halves.

Floral Appendage Variations

• Trimerous: Floral appendages in multiples of 3.
• Tetramerous: Floral appendages in multiples of 4.
• Pentamerous: Floral appendages in multiples of 5.

Presence of Bracts

• Bracteate: Possesses bracts.
• Ebracteate: No bracts present.

Flower Position Classification

• Hypogynous: Gynoecium is the highest; ovary is superior.
• Perigynous: Ovary in the center; other parts at the same level; ovary is half inferior.
• Epigynous: Thalamus encloses the ovary; other parts above; ovary is inferior.

Flower Parts

• Calyx (Sepals): Protects buds; can be gamosepalous (united) or polysepalous (free).
• Corolla (Petals): Brightly colored; can be gamopetalous (united) or polypetalous (free).

Aestivation Types

• Valvate: Margins touch without overlap.
• Twisted: One margin overlaps in one direction.
• Imbricate: Margins overlap in both directions.
• Vexillary: In five-petal flowers, the largest petal overlaps the others.

Androecium

• Male reproductive organ consisting of stamen (filament and anther).
• Sterile stamen is called a staminode.
• Anther typically bilobed with two pollen sacs per lobe.

Gynoecium

• Female reproductive part formed by carpels.
• Carpel Structure:
  • Style: Connects stigma to ovary.
  • Stigma: Receives pollen.
  • Ovary: Contains ovules.

Placentation Types

• Marginal: Placenta along the ventral suture; ovules on the ridge.
• Axile: Ovules attached in a multilocular ovary.
• Parietal: Ovules on the inner walls of the ovary.
• Free Central: Ovules on a central axis; no septa.
• Basal: Placenta at the base with a single ovule.

Monocotyledon

• Reference to a group of flowering plants with one cotyledon in the seed.