Introduction

• Whittaker’s Five Kingdom Classification (1969):
  • Monera, Protista, Fungi, Animalia, and Plantae.
  • Evolved over time due to advancements in understanding.

Evolution of Plant Kingdom Classification

• Dynamic Nature:
  • Changes in classification over time.
  • Exclusion of Fungi, Monera, and certain Protista from Plantae.

Kingdom Plantae

• Overview:
  • Includes Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms.
  • Dynamic understanding over time.

Concerns in Plant Classification

• Early Systems:
  • Based on superficial morphological characters.
  • Artificial, separated closely related species.
• Natural Classification:
  • Introduced by Bentham and Hooker.
  • Based on natural affinities, considering internal features.
• Phylogenetic Classification:
  • Based on evolutionary relationships.
  • Assumes common ancestry within taxa.

Modern Classification Approaches

• Numerical Taxonomy:
  • Uses computers to process observable characteristics.
  • Assigns numbers and codes to all characters.
• Cytotaxonomy:
  • Based on cytological information (chromosome number, structure, behavior).
• Chemotaxonomy:
  • Uses chemical constituents of plants to resolve classification challenges.

Algae

Introduction

• Characteristics:
  • Chlorophyll-bearing, simple, thalloid, autotrophic.
  • Largely aquatic, found in various habitats.
• Diversity:
  • Variable forms and sizes.
  • Ranging from colonial (e.g., Volvox) to filamentous (e.g., Ulothrix, Spirogyra).
  • Marine forms like kelps can be massive.

Reproduction

• Vegetative Reproduction:
  • Through fragmentation, each fragment develops into a thallus.
• Asexual Reproduction:
  • Production of spores, commonly zoospores.
  • Flagellated and motile, germinate to form new plants.
• Sexual Reproduction:
  • Fusion of two gametes.
  • Gametes can be flagellated and similar (isogamous) or non-flagellated but similar (isogamous).
  • Anisogamous reproduction in species like Eudorina.
  • Oogamous reproduction in species like Volvox, and Fucus.

Importance to Humans

• Carbon Fixation:
  • Algae contribute significantly to carbon dioxide fixation through photosynthesis.
• Oxygen Production:
  • Photosynthetic activity increases dissolved oxygen levels in their environment.
• Food Source:
  • Many marine algae species are used as food, e.g., Porphyra, Laminaria, and Sargassum.
• Industrial Uses:
  • Hydrocolloids (e.g., algin, carrageen) are commercially extracted from brown and red algae.
  • Agar from Gelidium and Gracilaria is used in microbiology and food.
• Food Supplements:
  • Chlorella, a unicellular alga rich in proteins, is used as a food supplement.

Classification

• Three Main Classes:
  • Chlorophyceae, Phaeophyceae, Rhodophyceae.

Chlorophyceae (Green Algae)

Characteristics:

• Plant Body:
  • Unicellular, colonial, or filamentous.
  • Typically grass is green due to dominant chlorophyll a and b pigments.
  • Chloroplasts exhibit various shapes (discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon-shaped).
  • The presence of storage bodies called pyrenoids in chloroplasts, containing protein and starch.
  • Rigid cell wall with an inner layer of cellulose and an outer layer of pectose.

Reproduction:

• Vegetative Reproduction:
  • Occurs through fragmentation or the formation of various types of spores.
• Asexual Reproduction:
  • Flagellated zoospores are produced in zoosporangia.

Sexual Reproduction:

• Shows variation in the type and formation of sex cells.
• Can be isogamous, anisogamous, or oogamous.

Commonly Found Green Algae:

1. Chlamydomonas
2. Volvox
3. Ulothrix
4. Spirogyra
5. Chara

Phaeophyceae (Brown Algae)

1. Habitat and Diversity
   • Primarily marine habitats.
   • Wide variation in size and form.
   • Ranging from simple branched, filamentous forms (e.g., Ectocarpus) to towering kelps reaching heights of up to 100 meters.
2. Pigments and Color Variation
   • Contain chlorophyll a, chlorophyll c, carotenoids, and xanthophylls.
   • Color ranges from olive green to various shades of brown, influenced by the amount of fucoxanthin pigment.
3. Storage of Food
   • Food is stored as complex carbohydrates like laminarin or mannitol.
4. Cellular Features
   • Vegetative cells have a cellulosic wall.
   • Covered by a gelatinous coating of algin on the outside.
   • The protoplast contains plastids, a centrally located vacuole, and a nucleus.
5. Plant Body Structure
   • Attached to the substratum by a holdfast.
   • Comprises a stalk (stipe) and leaf-like photosynthetic organ (frond).
6. Reproduction
   • Vegetative Reproduction: Occurs through fragmentation.
   • Asexual Reproduction: Typically involves biflagellate zoospores, pear-shaped with two unequal laterally attached flagella.
   • Sexual Reproduction: Can be isogamous, anisogamous, or oogamous. Union of gametes may occur in water or within the oogonium (in oogamous species). Gametes are pyriform and bear two laterally attached flagella.
7. Common Forms
   • Ectocarpus
   • Dictyota
   • Laminaria
   • Sargassum
   • Fucus

Rhodophyceae (Red Algae)

1. Pigmentation and Color
   • Predominantly red due to the presence of the red pigment r-phycoerythrin.
2. Habitat and Distribution
   • The majority are marine, with higher concentrations in warmer areas.
   • Occur in well-lighted regions close to the water surface and at greater depths in oceans with limited light penetration.
3. Thallus Structure
   • Typically multicellular red thalli.
   • Some species exhibit complex body organization.
4. Food Storage
   • Food stored as Floridian starch, structurally similar to amylopectin and glycogen.
5. Reproductive Modes
   • Vegetative Reproduction: Primarily occurs through fragmentation.
   • Asexual Reproduction: Involves non-motile spores.
   • Sexual Reproduction: Oogamous, characterized by non-motile gametes.
6. Post-Fertilization Developments
   • Sexual reproduction is accompanied by complex post-fertilization developments.
7. Common Members
   • Polysiphonia
   • Porphyra
   • Gracilaria
   • Gelidium

BRYOPHYTES (Mosses and Liverworts)

1. Habitat and Characteristics
   • Commonly found in moist shaded areas, especially in hills.
   • Often referred to as the amphibians of the plant kingdom due to their ability to live in soil but dependence on water for sexual reproduction.
   • Thrive in damp, humid, and shaded localities.
2. Ecological Role
   • Play a crucial role in plant succession on bare rocks and soil.
   • Form dense mats on the soil, reducing the impact of falling rain and preventing soil erosion.
   • Essential in decomposing rocks, making substrates suitable for higher plant growth.
3. Plant Body
   • Differentiated thallus-like structure, either prostrate or erect.
   • Attached to the substratum by unicellular or multicellular rhizoids.
   • Lack true roots, stems, or leaves.
   • May possess root-like, leaf-like, or stem-like structures.
4. Gametophyte and Sex Organs
   • The main plant body is haploid, termed gametophyte.
   • Sex organs are multicellular.
   • Male Sex Organ (Antheridium): Produces biflagellate antherozoids.
   • Female Sex Organ (Archegonium): Flask-shaped, produces a single egg.
5. Life Cycle
   • Zygotes do not undergo immediate reduction division.
   • Produce a multicellular body called sporophyte.
   • Sporophyte, attached to gametophyte, derives nourishment.
   • Some sporophyte cells undergo reduction division (meiosis) to produce haploid spores.
   • Spores germinate to form a new gametophyte.
6. Economic Importance
   • Mosses provide food for herbaceous mammals, birds, and other animals.
   • Sphagnum moss species provide peat used as fuel and packing material for trans-shipment due to water-holding capacity.
7. Ecological Importance
   • Mosses, along with lichens, are pioneers in colonizing rocks, contributing to ecological balance.
8. Classification
   • Bryophytes are divided into liverworts and mosses.

LIVERWORTS (Class Hepaticopsida)

1. Habitat and Characteristics
   • Typically found in moist, shady habitats such as stream banks, marshy areas, damp soil, tree bark, and wooded areas.
   • The plant body is thalloid, as seen in examples like Marchantia.
   • Dorsiventral thallus closely appressed to the substrate.
   • Some varieties have tiny leaf-like appendages arranged in two rows on stem-like structures.
2. Asexual Reproduction
   • Fragmentation: Liverworts reproduce asexually by the fragmentation of thalli.
   • Gemmae: Specialized structures called gemmae (singular: gemma) are formed. These are green, multicellular asexual buds.
   • Gemmae develop in gemma cups on the thalli, detach, and germinate to form new individuals.
3. Sexual Reproduction
   • Male and female sex organs can be produced on the same or different thalli.
   • Sporophyte Differentiation: Sporophyte has distinct parts – foot, seta, and capsule.
   • Capsule produces spores through meiosis.
   • Spores germinate to give rise to free-living gametophytes.
4. Role in Ecosystem
   • Liverworts contribute to the ecological balance, especially in maintaining moisture in their habitats.

MOSSES (Class Bryopsida)

1. Life Cycle Dominance
   • The primary stage in the life cycle of mosses is the gametophyte.
   • Gametophyte has two stages:
     • Protonema Stage: Develops directly from a spore. It is a creeping, green, branched, and often filamentous stage.
     • Leafy Stage: Develops from the secondary protonema as a lateral bud. Consists of upright, slender axes with spirally arranged leaves.
2. Attachment to Substrate
   • Attached to the soil through multicellular and branched rhizoids.
   • Rhizoids aid in absorption and anchorage.
3. Vegetative Reproduction
   • Fragmentation: Mosses reproduce vegetatively through fragmentation.
   • Budding: Budding occurs in the secondary protonema.
4. Sexual Reproduction
   • Sex Organs: Antheridia and archegonia are produced at the apex of leafy shoots.
   • Fertilization: After fertilization, the zygote develops into a sporophyte.
   • Sporophyte Structure: Consists of a foot, seta, and capsule.
   • Elaborate Capsule: The capsule is more elaborate compared to liverworts.
   • Spore Formation: Spores are formed through meiosis within the capsule.
5. Spore Dispersal Mechanism
   • Mosses exhibit an elaborate mechanism for spore dispersal.
6. Common Examples
   • Funaria, Polytrichum, and Sphagnum: Represent common examples of mosses.

PTERIDOPHYTES: HORSETAILS AND FERNS

1. Introduction
   • Definition: Pteridophytes encompass horsetails and ferns.
   • Utilization: Used for medicinal purposes and as soil binders; grown as ornamentals.
   • Evolutionary Significance: First terrestrial plants possessing vascular tissues (xylem and phloem).
2. Habitat and Distribution
   • Found in cool, damp, shady places; some thrive in sandy-soil conditions.
   • Limited geographical spread due to specific growth requirements and water dependence for fertilization.
3. Life Cycle
   • Dominant Phase: Sporophyte, differentiated into true root, stem, and leaves.
   • Vascular Tissues: Well-differentiated xylem and phloem present in roots, stem, and leaves.
   • Leaf Types: Small (microphylls) or large (macrophylls).
   • Sporangia: Located on sporophylls; may form strobili or cones (Selaginella, Equisetum).
4. Reproductive Process
   • Spore Formation: Spores produced by meiosis in sporangia.
   • Gametophyte: Multicellular, free-living, mostly photosynthetic thalloid gametophytes (prothallus).
   • Sex Organs: Antheridia (male) and archegonia (female) are present in gametophytes.
   • Fertilization: Water-dependent transfer of antherozoids to archegonia for fertilization.
   • Zygote Development: Zygote develops into a multicellular, well-differentiated sporophyte.
5. Spore Types
   • Homosporous: The majority of pteridophytes produce similar spores.
   • Heterosporous: Genera like Selaginella and Salvinia produce two kinds of spores (macro and micro).
6. Seed Habit
   • Precursor to the seed habit is considered an important step in evolution.
   • Female gametophytes in heterosporous plants retain young embryos on the parent sporophytes.
7. Classification
   • Four classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), and Pteropsida (Dryopteris, Pteris, Adiantum).

GYMNOSPERMS: PLANTS WITH NAKED SEEDS

1. Definition and Overview
   • Gymnosperms: “Gymnos” (naked), “Sperma” (seeds).
   • Ovules not enclosed by an ovary wall, remain exposed before and after fertilization.
   • Seeds are naked.
2. Morphology
   • Size: Medium-sized to tall trees and shrubs.
   • Notable Example: Giant redwood tree Sequoia, one of the tallest tree species.
   • Roots: Tap roots; mycorrhizal association in some (Pinus); coralloid roots with cyanobacteria in others (Cycas).
   • Stems: Unbranched (Cycas) or branched (Pinus, Cedrus).
   • Leaves: Simple or compound; adapted to extreme conditions with reduced surface area, thick cuticle, and sunken stomata.
3. Reproductive Characteristics
   • Heterosporous: Produces haploid microspores and megaspores.
   • Sporangia: Borne on sporophylls arranged spirally to form strobili or cones.
   • Microsporangiate Strobili: Male cones or strobili bearing microsporophylls and microsporangia.
   • Macrosporangiate Strobili: Female cones or strobili bearing megasporophylls with ovules or megasporangia.
   • Pollen Grain: Highly reduced male gametophyte; developed within microsporangia.
   • Ovule Development: Megaspore mother cell differentiates within the nucellus, forming ovules.
   • Female Gametophyte: Multicellular, retained within the megasporangium; bears archegonia or female sex organs.
4. Reproductive Process
   • Pollen Transfer: Pollen grains are released, carried by air currents, and come in contact with ovule openings.
   • Fertilization: Pollen tube grows toward archegonia, and discharges male gametes.
   • Seed Development: Following fertilization, the zygote develops into an embryo; ovules develop into seeds.
   • Seed Covering: Seeds are not covered.
5. Conclusion
   • Gymnosperms exhibit unique reproductive features with exposed ovules, naked seeds, and reduced independent gametophytic existence.
   • The adaptive leaf structures contribute to their resilience in diverse environmental conditions.

ANGIOSPERMS: FLOWERING PLANTS WITH ENCLOSED SEEDS

1. Introduction and Distinction from Gymnosperms
   • Angiosperms: Flowering plants with enclosed seeds.
   • Flower Development: Pollen grains and ovules develop in specialized structures called flowers.
   • Seed Enclosure: Seeds enclosed in fruits.
   • Habitat: Diverse, occurring in various habitats, ranging from Wolffia (smallest) to Eucalyptus (tall trees).
2. Economic Importance
   • Versatility: Provide food, fodder, fuel, medicines, and various commercially important products.
   • Ubiquity: Wide distribution and adaptation to diverse environments.
3. Classification
   • Two Main Classes: Dicotyledons and Monocotyledons.
4. Dicotyledons
   • Characteristics:
     • Two cotyledons in the seed.
     • Vascular bundles in the stem arranged in a ring.
     • Taproot system.
     • Leaves often have reticulate venation.
5. Monocotyledons
   • Characteristics:
     • Single cotyledon in the seed.
     • Vascular bundles in the stem scattered.
     • Fibrous root system.
     • Leaves often have parallel venation.
6. Conclusion
   • Angiosperms represent a vast and diverse group of plants with significant economic importance.
   • The development of flowers and fruit encapsulation of seeds are key features distinguishing them from gymnosperms.
   • Classification into dicotyledons and monocotyledons further categorizes this extensive plant kingdom.