🌿 Introduction
The Plant Kingdom (Plantae) comprises multicellular, eukaryotic, autotrophic organisms that use chlorophyll for photosynthesis. They are vital for maintaining life on Earth by producing oxygen, food, and shelter.
🧬 Characteristics of the Plant Kingdom
- Cell Type: Eukaryotic with distinct nucleus and organelles.
- Cell Wall: Made of cellulose.
- Nutrition: Autotrophic via photosynthesis.
- Reproduction: Both sexual and asexual.
- Reserve Food Material: Starch.
🌱 Evolutionary Perspective
Plants evolved from aquatic green algae (Chlorophyceae). Over time, they adapted to terrestrial environments by developing:
- Waxy cuticle to prevent water loss.
- Stomata for gas exchange.
- Conducting tissues (xylem & phloem).
- Seeds and flowers for reproduction.
🧾 Basis of Classification
According to R.H. Whittaker (1969), plants are classified based on:
- Cell Structure (Prokaryotic/Eukaryotic)
- Body Organization (Unicellular/Multicellular)
- Mode of Nutrition (Autotrophic/Heterotrophic)
- Reproduction (Asexual/Sexual)
- Phylogenetic Relationships (Evolutionary ancestry)
🪴 Major Divisions of Plant Kingdom
Plants are grouped into five major divisions:
| Division | Examples | Key Feature |
|---|---|---|
| Thallophyta (Algae) | Spirogyra, Ulva | Simple body, aquatic |
| Bryophyta | Funaria, Marchantia | Amphibians of plant kingdom |
| Pteridophyta | Marsilea, Ferns | Vascular plants without seeds |
| Gymnosperms | Cycas, Pinus | Naked seeds |
| Angiosperms | Mango, Rose | Enclosed seeds, flowers and fruits |
🌻 Alternation of Generations
Plants show two distinct life phases:
- Gametophytic phase – Haploid (n), produces gametes.
- Sporophytic phase – Diploid (2n), produces spores. These alternate in successive generations, varying among groups (algae to angiosperms).
🧠 Summary
- All plants are eukaryotic, multicellular, and autotrophic.
- The plant kingdom is classified into algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
- Evolution shows gradual adaptation to terrestrial habitats.
💡 Solved Examples
Q1. On what basis did Whittaker classify organisms?
A1. Whittaker’s classification was based on cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships.
Q2. Why are green plants called autotrophs?
A2. Because they synthesize their own food using sunlight, CO₂, and H₂O through photosynthesis.
Q3. Which group of plants is considered the amphibians of the plant kingdom?
A3. Bryophytes — they live on land but require water for fertilization.
Q4. What is alternation of generations?
A4. It is the alternation between haploid (gametophyte) and diploid (sporophyte) stages in a plant’s life cycle.
Q5. Which plant group first developed vascular tissues?
A5. Pteridophytes were the first plants to develop vascular tissues (xylem and phloem).