Comprehensive Guide to Kingdom Plantae and Plant Classification

Introduction to Kingdom Plantae and Classification Systems

• Five Kingdom Classification System: Proposed by Robert Whittaker in $1969$. The five kingdoms include:

  • Monera: Prokaryotic organisms.
  • Protista: Eukaryotic unicellular organisms.
  • Fungi: Heterotrophic eukaryotic organisms with cell walls.
  • Plantae: Autotrophic eukaryotic organisms with cell walls.
  • Animalia: Heterotrophic eukaryotic organisms without cell walls.

• Definition of Kingdom Plantae: This group consists of autotrophic living organisms having eukaryotic cells with cell walls. They are the main source of food for all other living organisms.

  • Autotrophy: Plants are autotrophic because they perform photosynthesis using chlorophyll.

• Eichler’s Classification ($1883$): The botanist Eichler classified Kingdom Plantae into two major subkingdoms:

  1. Cryptogams
  2. Phanerogams

Basis for Plant Classification

• First Criterion: The presence or absence of organs (roots, stems, leaves).
• Second Criterion: The presence or absence of separate conducting tissues (xylem and phloem) for the conduction of water and food.
• Third Criterion: Whether the plants bear seeds.
• Fourth Criterion: If seeds are present, whether they are enclosed within a fruit or not.
• Fifth Criterion: The number of cotyledons in the seeds (monocots or dicots).

Sub-kingdom: Cryptogams

• Etymology: Derived from "cryptos" (hidden) and "gams" (reproductive organs). Their reproductive organs are non-visible.
• General Characteristics: These plants reproduce by spore formation. They do not produce seeds or flowers.

Division I - Thallophyta

• Habitat: Grow mainly in water (fresh water or saline water).
• Structure: They do not have specific parts like roots, stems, leaves, or flowers. They have a soft, fiber-like body.
• Nutrition: Autotrophic due to the presence of chlorophyll; these are commonly called algae.
• Diversity: Can be unicellular or multicellular, and microscopic or large.
• Examples of Algae:
  • Spirogyra (characterized by spirally arranged green thread-like chloroplasts).
  • Ulothrix
  • Ulva
  • Sargassum
  • Chara
• Fungi Integration: Various types of fungi like yeasts and moulds, which lack chlorophyll, are also traditionally categorized under this group in some biological contexts.

Division II - Bryophyta

• Status: Known as the "amphibians" of the plant kingdom because they grow in moist soil but require water for reproduction.
• Morphology:
  • Thalloid, multicellular, and autotrophic.
  • Body structure is flat and ribbon-like.
  • Lack true roots, stems, and leaves.
  • Possess stem-like or leaf-like parts and root-like structures called rhizoids.
• Tissues: They do not have specific tissues for the conduction of food and water.
• Examples:
  • Moss (Funaria)
  • Marchantia
  • Anthoceros
  • Riccia

Division III - Pteridophyta

• Morphology: Have well-developed roots, stems, and leaves.
• Conduction: Possess separate tissues (conducting system) for the conduction of food and water.
• Reproduction:
  • Do not bear flowers or fruits.
  • Reproduce asexually via spores formed along the back or posterior surface of their leaves (in structures called sporangia or sori).
  • Reproduce sexually by zygote formation.
• Examples:
  • Ferns like Nephrolepis, Marsilea, Pteris, Adiantum, Equisetum, Selaginella, and Lycopodium.

Sub-kingdom: Phanerogams

• Characteristics: Plants that have special structures for reproduction and produce seeds. Seeds contain an embryo and stored food used for the initial growth of the embryo during germination.
• Classification: Based on seed enclosure, they are divided into Gymnosperms and Angiosperms.

Division I - Gymnosperms

• Etymology: Derived from "gymnos" (naked) and "sperms" (seeds).
• Nature: Mostly evergreen, perennial, and woody.
• Morphology:
  • Stems are typically without branches.
  • Leaves form a crown at the top.
• Reproduction: Bear male and female flowers on different sporophylls of the same plant. Seeds lack a natural covering (no fruit formation).
• Examples:
  • Cycas
  • Picea (Christmas tree)
  • Thuja (Morpankhi)
  • Pinus (Deodar)

Division II - Angiosperms

• Etymology: Derived from "angios" (cover) and "sperms" (seeds).
• Characteristics: The flowers are the reproductive organs. Flowers develop into fruits, and seeds are formed within those fruits (covered seeds).
• Classification: Based on the number of cotyledons.

Comparison of Dicotyledonous and Monocotyledonous Plants

Questions & Discussion

• Can you recall? How have living organisms been classified? Living organisms are classified based on cell type (Prokaryotic/Eukaryotic), body organization (Unicellular/Multicellular), and mode of nutrition (Autotrophic/Heterotrophic) into Five Kingdoms.
• Can you tell? Which special cell organelles differentiate plant cells from animal cells? Plant cells contain cell walls and chloroplasts (which contain chlorophyll), which are absent in animal cells.
• Observation Task (Spirogyra): To observe Spirogyra, collect green fibers from a pond, wash them, and place them on a glass slide. Under a microscope, one observes spirally arranged green thread-like chloroplasts.
• Observation Task (Bryophyta): Green carpets on old walls or bricks in the rainy season are typically mosses or bryophytes.
• Use your brain power! What is the similarity between Thallophyta, Bryophyta, and Pteridophyta? Irrespective of their body structures, they all reproduce by spore formation and are called Cryptogams because their reproductive organs are hidden.
• Try this (Seed Categorization): Soak seeds of corn, beans, groundnut, tamarind, mango, and wheat in water for $8 \text{ to } 10 \text{ hours}$. Check if they divide into two equal halves (dicots) or not (monocots).