Summary & Tables
Chapter Overview: Classification Systems
The classification of the Plant Kingdom has evolved significantly over time:
- Artificial Systems (e.g., Linnaeus): Based on superficial morphological characters (habit, color, leaf shape). Now discarded as they separated closely related species and were easily affected by environment.
- Natural Systems (e.g., Bentham & Hooker): Based on natural affinities including ultrastructure, anatomy, and phytochemistry.
- Phylogenetic Systems (Current): Based on evolutionary relationships, assuming organisms in the same taxa share a common ancestor.
| Feature | Chlorophyceae (Green) | Phaeophyceae (Brown) | Rhodophyceae (Red) |
|---|---|---|---|
| Common Forms | Chlamydomonas, Volvox, Spirogyra | Ectocarpus, Laminaria, Sargassum | Polysiphonia, Porphyra, Gelidium |
| Pigments | Chlorophyll a, b | Chlorophyll a, c, Fucoxanthin | Chlorophyll a, d, r-phycoerythrin |
| Stored Food | Starch | Mannitol, Laminarin | Floridean Starch |
| Cell Wall | Cellulose | Cellulose & Algin | Cellulose, pectin, polysulphate esters |
| Flagella | 2-8, equal, apical | 2, unequal, lateral | Absent |
| Habitat | Fresh, Brackish, Salt | Fresh (rare), Brackish, Salt | Mostly Marine (Warmer areas) |
Algae & Bryophytes
Algae: Chlorophyll-bearing, simple, thalloid organisms. They are ecologically vital, performing 50% of earth's CO2 fixation. They reproduce vegetatively (fragmentation), asexually (zoospores), and sexually (isogamous, anisogamous, or oogamous).
Bryophytes: The "Amphibians of the Plant Kingdom".
- They live in soil but depend on water for sexual reproduction.
- Dominant body is the haploid Gametophyte.
- Sporophyte is not free-living; it remains attached to the gametophyte.
- Includes Liverworts (e.g., Marchantia) and Mosses (e.g., Funaria).
- Economic importance: Peat (fuel), packing material, and soil binders.
| Feature | Bryophytes | Pteridophytes |
|---|---|---|
| Dominant Phase | Gametophyte (Haploid, n) | Sporophyte (Diploid, 2n) |
| Vascular Tissue | Absent | Present (Xylem & Phloem) |
| Differentiation | Thallus-like, root-like structures (Rhizoids) | True roots, stems, and leaves |
| Sporophyte Nature | Parasitic/Dependent on Gametophyte | Independent, dominant plant body |
| Examples | Marchantia, Funaria | Selaginella, Equisetum, Ferns |
Pteridophytes & Gymnosperms
Pteridophytes: First terrestrial plants with vascular tissue. The main plant body is a Sporophyte. Most are homosporous, but some (e.g., Selaginella) are heterosporous.
Gymnosperms: "Naked Seed" plants.
- Ovules are not enclosed by an ovary wall; seeds remain exposed.
- Includes medium to tall trees (e.g., Sequoia, Pinus, Cycas).
- Leaves are adapted to extreme conditions (needle-like, sunken stomata).
- Unlike lower plants, gametophytes do not have an independent free-living existence.
| Group | Main Body | Vascular Tissue | Reproduction | Seed Habit |
|---|---|---|---|---|
| Algae | Thallus (n) | Absent | Zoospores, Gametes (Water req.) | Absent |
| Bryophytes | Gametophyte (n) | Absent | Water required for fertilization | Absent |
| Pteridophytes | Sporophyte (2n) | Present | Water required; Prothallus formed | Precursor |
| Gymnosperms | Sporophyte (2n) | Present | No water required (Wind); Cones | Present (Naked) |
| Angiosperms | Sporophyte (2n) | Present | Flowers; Double Fertilization | Present (In Fruit) |
Angiosperms (Flowering Plants)
In Angiosperms, pollen grains and ovules develop in specialized structures called flowers, and seeds are enclosed in fruits. They are divided into:
- Dicotyledons: Have two cotyledons in the seed.
- Monocotyledons: Have only one cotyledon.
They provide food, fodder, fuel, medicines, and are the most dominant plant group on earth.