2. Floral Diversity
2.1 Introduction to Biological Classification
Biological classification is the process by which living organisms are categorized based on shared characteristics. This systematic approach allows scientists to study the vast diversity of life efficiently.
Three Domains of Life (Woese Classification)
Based on molecular differences in ribosomal RNA, Carl Woese proposed a three-domain system:
- Bacteria: Single-celled prokaryotic organisms with peptidoglycan in their cell walls.
- Archaea: Prokaryotic organisms that often live in extreme environments; they lack peptidoglycan in their cell walls.
- Eukarya: Organisms whose cells contain a nucleus and membrane-bound organelles, including protists, fungi, plants, and animals.
Binomial Nomenclature
Developed by Carolus Linnaeus, this system provides a unique two-part scientific name for every species:
- Genus: The first part, which is always capitalized.
- Species: The second part, which is written in lowercase.
- Rules: The name must be italicized when typed or underlined when handwritten. For example, the scientific name for humans is Homo sapiens.
Whittaker' | Five Kingdom Classification
Robert Whittaker proposed a system based on cell structure, mode of nutrition, and body organization:
- Monera: Unicellular prokaryotes (e.g., Bacteria).
- Protista: Unicellular eukaryotes.
- Fungi: Multicellular/unicellular heterotrophs with chitinous cell walls.
- Plantae: Multicellular autotrophs with cellulose cell walls.
- Animalia: Multicellular heterotrophs without cell walls.
Flora and Biodiversity in Nepal
Nepal is recognized as a global biodiversity hotspot due to its diverse topography and climatic zones. The country hosts a high number of endemic species (species found nowhere else in the world), making its conservation critical for global ecological balance.
2.2 Fungi: The Heterotrophic Decomposers
Fungi are eukaryotic, heterotrophic organisms that lack chlorophyll. Their cell walls are composed of chitin. Most fungi exist as a network of thread-like structures called mycelium, which is composed of individual filaments known as hyphae.
Classification of Fungi
| Class | Characteristics | Examples |
|---|---|---|
| Phycomycetes | Coenocytic hyphae (multinucleate); asexual reproduction via zoospores. | Mucor, Rhizopus |
| Ascomycetes | Known as "sac fungi"; produce spores in a sac called an ascus. | Yeast, Penicillium |
| Basidiomycetes | "Club fungi"; produce spores on a structure called a basidium. | Mushrooms, Puccinia |
| Deuteromycetes | "Imperfect fungi"; sexual stage is unknown or absent. | Alternaria |
Detailed Study: Mucor and Yeast
Mucor Structure and Reproduction
Mucor consists of a mycelium that grows on organic substrates. It reproduces asexually through sporangia supported by sporangiophores. During sexual reproduction, fusion of gametes leads to the formation of a thick-walled zygospore.
Yeast Structure and Reproduction
Unlike many fungi, Yeast is unicellular. It reproduces asexually through budding, where a small outgrowth forms a new cell. Sexually, yeast can form ascospores within an ascus.
Edible and Poisonous Fungi
- Edible: Agaricus bisporus (common button mushroom).
- Poisonous: Amanita phalloides (Death Cap).
Economic Importance of Fungi
- Decomposition: Act as primary decomposers in ecosystems.
- Antibiotics: Species like Penicillium are used to produce life-saving drugs.
- Food: Mushrooms are a vital source of nutrition.
- Symbiosis: Mycorrhiza (fungi + plant roots) aids in nutrient absorption.
- Diseases: Cause infections in humans (ringworm) and crops.
2.3 Lichens: The Symbiotic Pioneers
Lichens represent a symbiotic association between an alga (the phycobiont, providing food via photosynthesis) and a fungus (the mycobiont, providing shelter and minerals).
Morphological Forms:
- Crustose: Crust-like, tightly attached to the substrate.
- Foliose: Leaf-like, with distinct upper and lower surfaces.
- Fruticose: Shrub-like, branched structures.
Economic Importance: Lichens are highly sensitive to air pollution (especially SO2) and serve as pollution indicators. They are also used as dyes, medicines, and food for animals like reindeer.
2.4 Algae: The Aquatic Autotrophs
Algae are chlorophyll-containing, autotrophic organisms found primarily in aquatic environments.
Major Classes of Algae
- Chlorophyceae (Green Algae): Contain chlorophyll a and b; cell walls are made of cellulose. Examples: Spirogyra, Chlamydomonas.
- Phaeophycece (Brown Algae): most possess the pigment fucoxanthin. They store food as laminarin. Examples: Sargassum, Fucus.
- Rhodophycece (Red Algae): Contain phycoerythrin. They are commercially important for producing agar and carrageenan.
Detailed Study: Spirogyra
Spirogyra is a filamentous green algae characterized by spiral-shaped chloroplasts. It undergoes scalariform conjugation, a type of sexual reproduction where genetic material moves through a conjugation tube to form a zygospore.
Economic Importance of Algae
- Food: Many seaweeds are eaten directly. Spirulina is a nutrient-rich supplement.
- Industrial: Agar (from red algae) is used in labs; alginates are used in food-thickening.
- Biofuel: Algae are being researched as a source of renewable energy.
2.5 Bryophyta: The Amphibians of the Plant Kingdom
Bryophytes lack true vascular tissue (xylem and phloem) and require water for fertilization, earning them the name "amphibians of the plant kingdom."
Classification of Bryophytes
- Liverworts: Thalloid-shaped bodies. Marchantia is a classic example. They reproduce asexually via gemmae (small multicellular bodies in gemmae cups).
- Hornworts: Characterized by horn-shaped sporophytes. Example: Anthoceros.
- Mosses: Mosses possess a leafy gametophyte and a protonema stage. Example: Funaria.
Economic Importance of Bryophytes
They aid in soil formation by breaking down rocks, help in water retention in forest floors, and contribute to peat formation (used as fuel).
2.6 Pteridophyta: The First Vascular Plants
Pteridophytes represent the evolutionary leap to vascular tissue (xylem and phloem). They possess true roots, stems, and leaves.
Study of Dryopteris
Dryopteris (a fern) features:
- Rhizome: An underground stem.
- Fronds: Large, divided leaves.
- Sori: Clusters of sporangia found on the underside of leaves.
- Prothallus: heart-shaped gametophyte.
Economic Importance: Used for ornamentation, medicinal purposes, and as soil binders.
2.7 Gymnosperms: The Naked Seed Plants
Gymnosperms produce seeds that are not enclosed within an ovary (naked seeds). They are typically perennial, woody plants.
Characteristics and Pinus
Gymnosperms possess xylem with tracheids but lack vessels, and phloem lacks sieve tubes. Pinus is a prominent-example:
- Morphology: Features needle-like leaves to reduce transpiration.
- Reproduction: Produnded by male and female cones.
- Symbiosis: Many species form mycorrhizal associations with fungi to assist nutrient uptake.
Economic Importance: Provides timber, resin, turpentine, and paper pulp.
2.8 Angiosperms: The Flowering Plants
Angiosperms are highly evolved plants where seeds are enclosed within fruits. They are characterized by the presence of flowers.
Taxonomic Hierarchy
Taxonomy is the science of identification, nomenclature, and classification. The hierarchy follows this order:
Kingdom → Division → Class → Order → Family → Genal → Species
Classification Systems
- Artificial System: Based on superficial characters (e.e., Linnaeus).
- Natural System: kind: Based on many natural characters (Bentham & Hooker).
- Phylogenetic System: Based on evolutionary relationships (Engler & Prantl).
Study of Key Families
| Family | Key Characteristics | Examples |
|---|---|---|
| Brassicaceae | Cruciform flowers, 4+2 stamens, silique fruit. | Mustard, Cabbage |
| Fabaceae | Papilionaceous flower, legume fruit, 10 stamens (diadelphous). | Pea, Beans |
| Solanaceae | Gamopetalous corolla, berry or capsule fruit. | Potato, Tomato |
| Liliaceae | Trimerous flowers, superior ovary, bulbous stems. | Onion, Tulip |
Note: Each-family plays a vital role in human-food-security and ecological-stability.