Unit-I: Morphology of Vegetative Parts and Inflorescence
1. Characteristic Features of Angiosperms
Angiosperms, commonly known as flowering plants, represent the most diverse and dominant group of land plants. Their primary distinguishing feature is the production of flowers and the protection of seeds within a fruit derived from an ovary.
Definition: Angiosperms are vascular plants where the ovules are enclosed within an ovary, which matures into a fruit after fertilization.
- Vascular System: Highly developed xylem (containing vessels) and phloem (containing sieve tubes and companion cells).
- Double Fertilization: A unique process resulting in a diploid zygote and a triploid endosperm.
- Seed Habit: Seeds are enclosed within fruits, facilitating various dispersal mechanisms.
2. Study of Modified Root and Stem
Plants often modify their vegetative organs to perform specialized functions like storage, support, or respiration.
A. Root Modifications
- Storage Roots: Taproots (e.g., Carrot - Conical, Radish - Fusiform) or Adventitious roots (e.g., Sweet Potato) that swell to store nutrients.
- Supportive Roots:
- Prop Roots: Grow vertically downwards from aerial branches (e.g., Banyan tree).
- Stilt Roots: Grow from lower nodes of the stem for extra support (e.g., Maize, Sugarcane).
- Respiratory Roots (Pneumatophores): Found in halophytes; these grow upwards to obtain oxygen (e.g., Rhizophora).
B. Stem Modifications
- Underground (Storage): Rhizome (Ginger), Tuber (Potato), Bulb (Onion), and Corm (Colocasia).
- Sub-aerial (Propagation): Runner (Grasses), Stolon (Strawberry), Offset (Water Hyacinth), and Sucker (Chrysanthemum).
- Aerial (Specialized):
- Tendrils: For climbing (e.g., Grapevine).
- Thorns: For protection (e.g., Bougainvillea).
- Phylloclade: Green, fleshy stem performing photosynthesis (e.g., Opuntia).
3. Bud and its Modifications
A bud is a condensed embryonic shoot. Based on position, they are classified as terminal (apical) or axillary.
Modifications:
- Bulbils: Fleshy buds meant for vegetative propagation (e.g., Agave, Dioscorea).
- Floral Buds: Modified for sexual reproduction, eventually becoming flowers.
- Protection: Some buds are covered by "bud scales" to survive dormant periods.
4. Leaf Morphology: Venation, Phyllotaxy, and Modifications
A. Venation
The arrangement of veins and veinlets in the leaf lamina.
B. Phyllotaxy
The pattern of arrangement of leaves on the stem.
- Alternate: Single leaf at each node (e.g., China rose).
- Opposite: Pair of leaves at each node (e.g., Guava, Calotropis).
- Whorled: More than two leaves at a node (e.g., Alstonia).
C. Leaf Modifications
- Tendrils: For climbing (e.g., Peas).
- Spines: For defense and reducing transpiration (e.g., Cacti).
- Storage: Fleshy leaves for storing water or food (e.g., Aloe, Onion).
- Phyllode: Modified petiole that becomes green and leaf-like (e.g., Australian Acacia).
5. Types of Stipules and its Modifications
Stipules are small, leaf-like appendages found at the base of the petiole.
- Free-lateral: Two small green stipules on either side (e.g., Hibiscus).
- Adnate: Attached to the petiole (e.g., Rose).
- Ochreate: Form a tube-like covering around the node (e.g., Polygonum).
- Spiny: Modified into thorns for protection (e.g., Ziziphus).
- Tendrillar: Modified into tendrils for climbing (e.g., Smilax).
6. Leaf Texture, Shape, Apex, and Base
Detailed morphological descriptions are vital for plant identification and taxonomy.
- Texture: Can be coriaceous (leathery), herbaceous (thin/soft), or succulent (fleshy).
- Shape: Common shapes include Acicular (needle-like), Lanceolate (spear-shaped), Ovated (egg-shaped), and Cordate (heart-shaped).
- Apex: Examples include Acute (sharp point), Obtuse (rounded), or Caudate (tail-like).
- Base: Can be Cuneate (wedge-shaped), Cordate (heart-shaped), or Oblique (asymmetrical).
7. Origin, Evolution, and Types of Inflorescences
The arrangement of flowers on the floral axis (peduncle) is called the inflorescence.
A. Major Types
- Racemose: Indeterminate growth; main axis continues to grow. Flowers are in acropetal succession.
- Cymose: Determinate growth; main axis terminates in a flower. Flowers are in basipetal succession.
B. Special Types
- Cyathium: Looks like a single flower but is a group of flowers (e.g., Euphorbia).
- Hypanthodium: Fleshy receptacle forming a hollow cavity with an apical opening (e.g., Ficus/Fig).
- Verticillaster: A condensed dichasial cyme at the axil of leaves (e.g., Ocimum/Tulsi).
8. Exam Preparation
Exam Tip: Always draw neat, labeled diagrams for modifications. For inflorescences, clearly distinguish between acropetal (Racemose) and basipetal (Cymose) arrangements to score high.
Common Mistake: Confusing Phylloclade (stem modification) with Phyllode (leaf modification). Remember: Phylloclade starts with 'S' sound for Stem (clade/stem), while Phyllode involves the Petiole.
Frequently Asked Questions (FAQ)
- Q: What is the evolutionary significance of the inflorescence?
A: It increases pollination efficiency by grouping flowers, making them more visible to pollinators and ensuring better seed set.
- Q: What are Pneumatophores?
A: These are respiratory roots found in swampy/mangrove areas that grow vertically out of the soil to facilitate gas exchange.