🌸 Introduction

Angiosperms, or flowering plants, are the most advanced and diverse group in the plant kingdom whhich are characterized by the presence of flowers and seeds enclosed within fruits. They are an exceptionally large group, occurring in a wide range of habitats, from the tiniest Wolffia to tall trees like Eucalyptus (over 100 meters).

They produce flowers, fruits, and seeds enclosed within an ovary — hence called covered seed plants (Greek: angio = covered, sperma = seed).

They dominate all terrestrial ecosystems and exhibit a wide range of forms from tiny herbs to massive trees.

🌱 General Characteristics

  • Habitat: Found in almost all environments — aquatic, terrestrial, and epiphytic.
  • Plant Body: Differentiated into true roots, stems, and leaves.
  • Vascular Tissue: Well-developed xylem and phloem with vessels and companion cells.
  • Reproduction: By flowers — specialized reproductive structures.
  • Seeds: Enclosed within fruits.
  • Dominant Generation: Sporophyte.
  • Sporophyte is the dominant plant body, differentiated into roots, stems, and leaves.
  • Possess highly developed vascular tissues (xylem with vessels, phloem with companion cells).
  • Provide us with food, fodder, fuel, medicines, and several other commercially important products.

🌼 Classification

Angiosperms are divided into two main classes:

  1. Dicotyledons:
    • Characterized by having two cotyledons in their seeds.
    • Exhibit reticulate venation in leaves.
    • Flowers are typically tetramerous or pentamerous (floral whorls in multiples of 4 or 5).
    • Have a primary tap root system.
    • Vascular bundles are arranged in a ring and are open (allowing secondary growth).
  2. Monocotyledons:
    • Characterized by having only one cotyledon in their seeds.
    • Exhibit parallel venation in leaves.
    • Flowers are typically trimerous (floral whorls in multiples of 3).
    • Have a fibrous root system.
    • Vascular bundles are scattered and are closed (lacking cambium).
Feature Monocotyledons Dicotyledons
Number of cotyledons One Two
Leaf venation Parallel Reticulate
Vascular bundles Scattered In ring
Root system Fibrous Taproot
Floral parts Multiples of 3 Multiples of 4 or 5
Example Wheat, Maize, Onion Mango, Pea, Rose

🌸 Structure of Flower and Reproduction

  1. Flower: The reproductive organ consisting of sepals, petals, stamens, and carpels.
  2. Pollination: Transfer of pollen from anther to stigma (by wind, water, or animals).
  3. Fertilization: Occurs inside the ovary.

Reproduction

  • Flowers: The flower is the reproductive structure of angiosperms.
  • Sex Organs:
  • Stamen (Male): Consists of a filament and an anther. The anther produces pollen grains (male gametophytes) after meiosis.
  • Pistil/Carpel (Female): Consists of stigma, style, and ovary. The ovary contains one to many ovules.
  • Female Gametophyte (Embryo Sac): Within the ovule is the highly reduced female gametophyte, known as the embryo sac. It develops from the functional megaspore (formed after meiosis in the megaspore mother cell). A typical mature embryo sac is 7-celled and 8-nucleate (containing 1 egg cell, 2 synergids, 3 antipodal cells, and 1 central cell with 2 polar nuclei).
  • Pollination: Transfer of pollen grains from the anther to the stigma. Agents can be wind, water, insects, or other animals.
  • Post-fertilization:

💫 Double Fertilization

A unique feature of angiosperms:

  1. The pollen grain germinates on the stigma, and the pollen tube grows through the style to reach the ovule.
  2. The pollen tube enters the embryo sac and releases two male gametes.
  3. Syngamy: One male gamete fuses with the egg cell to form the diploid zygote (2n).
  4. Triple Fusion: The other male gamete fuses with the diploid secondary nucleus (formed by the fusion of the two polar nuclei) in the central cell to produce the triploid primary endosperm nucleus (PEN) (3n).

This process ensures development of both embryo and nutritive tissue simultaneously.

🌾 Fruit Formation (Post-fertilization)

  • The zygote develops into the embryo (with one or two cotyledons).
  • The PEN develops into the endosperm, which provides nourishment to the developing embryo.
  • Synergids and antipodal cells degenerate.
  • The ovule develops into the seed.
  • The ovary develops into the fruit, which encloses the seed(s).

🌿 Economic Importance

Use Example
Food Rice, Wheat, Maize, Potato
Fibre Cotton, Jute
Medicine Rauwolfia, Cinchona
Timber Teak, Sal
Ornamental Rose, Hibiscus

🧠 Summary

  • Angiosperms produce flowers, fruits, and seeds enclosed in ovary.
  • Divided into monocots and dicots.
  • Exhibit double fertilization and endosperm formation.
  • Most dominant plant group on Earth.

💡 Solved Examples

Q1. What distinguishes angiosperms from gymnosperms?
A1. Seeds in angiosperms are enclosed within fruits; in gymnosperms they are naked.

Q2. What is double fertilization?
A2. One male gamete fuses with egg to form zygote, another fuses with two polar nuclei to form triploid endosperm.

Q3. Give one feature common to monocots and dicots.
A3. Both have vascular tissues with xylem and phloem.

Q4. What is the function of endosperm?
A4. Endosperm provides nutrition to the developing embryo.

Q5. Name two economically important angiosperms.
A5. Oryza sativa (rice) and Gossypium (cotton).