Plant Kingdom

1. Systems of Classification & Botanical Terminology

A. Systems of Classification

B. Key Plant Kingdom Terminology

• Gametophyte ($n$): Multicellular haploid phase producing gametes ($n$) via Mitosis.
• Sporophyte ($2n$): Multicellular diploid phase producing spores ($n$) via Meiosis (Except Algae where zygote undergoes meiosis).
• Spermatophyta: Seed-bearing plants $\to$ Gymnosperms & Angiosperms.
• Archegoniate: Female sex organ (Archegonium) bearing plants $\to$ Bryophytes, Pteridophytes, Gymnosperms.
• Tracheophyta: Vascular bundle (Xylem & Phloem) bearing plants $\to$ Pteridophytes, Gymnosperms, Angiosperms.
• Embryophyta: Plants producing embryo ($\text{Zygote} \to \text{Embryo}$) $\to$ Bryophytes to Angiosperms (Algae excluded!).
• Cryptogamae vs. Phanerogamae: Cryptogamae have hidden sex organs (Algae, Bryo, Pterido); Phanerogamae have exposed sex organs (Gymno, Angio).

C. Overview of Algae (Thallophyta)

• Simple, thalloid, autotrophic, chlorophyll-bearing, aquatic (freshwater & marine) gametophytes. Non-embryonic, atracheophyte, cryptogamic.
• Associations: Symbiotic with Fungi ($\to$ Lichens) or Epizootic on Animals (e.g., Sloth bear).
• Forms: Colonial ($\text{Volvox}$), Filamentous ($\text{Ulothrix, Spirogyra}$), Massive kelps (up to $100\text{ meters}$).
• Reproduction & Gametes:

  • Isogamous non-flagellated: $\text{Spirogyra}$.

  • Isogamous flagellated: $\text{Ulothrix}$.

  • Anisogamous: $\text{Eudorina}$.

  • Oogamous: $\text{Volvox, Fucus}$.

• Economic Uses: Fixes $50\%$ of global $\text{CO}_2$; Hydrocolloids $\to$ Algin (brown algae), Carrageen (red algae), Agar-Agar (from $\text{Gelidium}$ and $\text{Gracilaria}$). Single cell protein $\to$ $\text{Chlorella}$. Food $\to$ $\text{Sargassum, Laminaria, Porphyra}$.

2. Classification of Algae & Introduction to Bryophytes

A. Comparative Table of Algae Classes

B. Bryophytes (“Amphibians of Plant Kingdom”)

• Thalloid or erect, 1st Embryophytes, Atracheophytes, Aspermatophytes. Homosporous.
• Live in damp, shaded soil but depend on external water for sexual reproduction (flagellated antherozoids swim to egg).
• Dominant plant body is independent, free-living Gametophyte ($n$) attached to substrate by unicellular or multicellular Rhizoids.
• Multicellular sex organs: Male Antheridium (biflagellated antherozoids) & Female flask-shaped Archegonium (single egg cell).

3. Bryophyte Classes & Pteridophytes Overview

A. Bryophyte Life Cycle & Classification

• Sporophyte ($2n$): Differentiated into Foot, Seta, Capsule. Not free-living; remains attached to and nutritionally dependent on gametophyte. Spore mother cells in capsule undergo meiosis $\to$ Haploid Spores ($n$).
• 1. Liverworts (e.g., Marchantia): Dorsiventral, flattened thallus.

  • Asexual Reproduction: Fragmentation or specialized green multicellular asexual buds called Gemmae housed in Gemma Cups on dorsal thallus.

  • Sex organs borne on specialized erect stalks (Antheridiophore & Archegoniophore).

• 2. Mosses (e.g., Funaria, Polytrichum, Sphagnum): Two distinct gametophytic stages:

  • Juvenile Protonema Stage: Creeping, green, branched, filamentous stage developing directly from spore.

  • Adult Leafy Stage: Upright, slender spiral leafy axis bearing sex organs at apex.

  • Economic Importance: Sphagnum (Peat Moss) used as fuel and packing material for trans-shipment due to water holding capacity. Mosses $+$ Lichens pioneer ecological succession on bare rocks.

B. Pteridophytes (First Vascular Land Plants)

• Includes Horsetails and Ferns. 1st land plants with true vascular tissues (Xylem & Phloem). Aspermatophytes.
• Dominant phase is independent, true plant body Sporophyte ($2n$) differentiated into true roots, stem, and leaves.
• Leaves: Microphylls (small leaves; e.g., Selaginella) or Megaphylls (large fronds; e.g., Ferns).
• Sporophylls & Cones: Sporangia borne on leaf-like appendages called Sporophylls. May form compact structures called Strobili / Cones (e.g., Selaginella, Equisetum).
• Heterospory & Seed Habit Precursor:

  • Most pteridophytes are Homosporous (produce identical spores).

  • Selaginella and Salvinia are Heterosporous (produce Microspores $\to$ male gametophyte and Megaspores $\to$ female gametophyte).

  • Retention of female gametophyte on parent sporophyte is an important step in evolution $\to$ Precursor to Seed Habit!

4. Pteridophyte Classes, Gymnosperms & Angiosperms

A. Prothallus & Pteridophyte Classes

• Prothallus: Spores germinate to form an inconspicuous, small, multicellular, free-living, photosynthetic haploid gametophyte called Prothallus. Requires cool, damp, shady places (restricts geographical distribution).
• 4 Classes of Pteridophytes:

  1. Psilopsida: Psilotum.

  2. Lycopsida: Selaginella, Lycopodium.

  3. Sphenopsida: Equisetum (Horsetail).

  4. Pteropsida: Dryopteris, Pteris, Adiantum (Walking fern).

B. Gymnosperms (“Naked Seeds”)

• Ovules not enclosed by any ovary wall; remain exposed both before and after fertilization. Seeds are naked (no fruits!).
• Phanerogams, Tracheophytes (Xylem lacks vessels, phloem lacks companion cells – contain sieve cells). All are strictly Heterosporous.
• Dominant Sporophyte ($2n$): Male and female gametophytes do not have an independent free-living existence; remain retained within sporangia on parent sporophyte.
• Endosperm in Gymnosperms: Formed before fertilization $\to$ Always Haploid ($n$)!

C. Pinus vs. Cycas Comparison