Study Notes on Plant Morphology

CHAPTER 3: PLANT MORPHOLOGY

THE EXTERNAL FORM OF PLANTS

PLANT MORPHOLOGY

• Morphology is defined as the study of the form and structure of organisms and their specific structural features.

• It encompasses the outward appearance of plants, including shape, structure, color, and pattern.

• Components of flowering plants include:

  • Root system (the underground part consisting of roots)

  • Shoot system (the above-ground part consisting of stems, leaves, and flowers)

• A flowering plant primarily consists of:

  1. Roots

  2. Stem

  3. Leaves

  4. Flowers

  5. Fruits

  6. Seeds

Morphology of Flowering Plants

Structure Overview

• Shoot System

  • Includes parts like Flower, Leaf, Stem, Bud, Node, Internode.

• Root System

  • Includes Primary Root, Secondary Roots, and Lateral Roots.

The Root

Endosperm

• Main features of the root include:

  • Develops from the radicle of the embryo.

  • Generally non-green and cylindrical in structure.

  • Does not exhibit nodes and internodes.

Characteristics of the Root

• Roots have the following characteristics:

  • Develop from the radicle of the embryo.

  • Typically are non-green and cylindrical.

  • Lack nodes and internodes.

Functions of Roots

• Roots perform several essential functions:

  • Anchor the plant into the soil.

  • Absorb water and dissolved mineral nutrients from the soil.

  • Store nutrients such as surplus sugars and starch.

  • Conduct/transport water and nutrients.

  • Engage in vegetative reproduction.

Types of Roots

Tap Roots or True Roots

• Tap roots develop from the radicle during seed germination and are characterized as true roots.

• The main root is referred to as the primary root, with branches of the first order termed secondary roots and those of the secondary order called tertiary roots.

• A tap root system is a characteristic of dicotyledonous plants which grows predominantly downwards.

• Acropetal succession in lateral branching means older and longer branches are located at the base, while younger, shorter ones are near the apex.

Adventitious Root System

• Defined as roots that develop from any part of the plant other than the radicle.

• Common sites of adventitious root development include:

  • Base of the stem

  • Nodes and leaves

• In monocots, the radicle is short-lived, leading to the formation of equal-sized adventitious roots, collectively termed a fibrous root system (for example, in maize, wheat, sugarcane).

• Fibrous roots generally do not penetrate deeply into the soil.

Root System Types

• Taproot System:

  • One main, dominant root (the tap root) grows deeper.

  • Typical in dicots and characterized by natural drought resistance.

• Fibrous Root System:

  • Comprises numerous thin roots of equal size without a central tap root.

  • Common in monocots, including grasses, these systems are effective in anchoring plants and preventing soil erosion.

Morphology of Stem

General Structure

• Stems are the above-ground organs of plants that support leaves and fruits while conducting water and sugars (via xylem and phloem).

• Key characteristics include:

  • Composed of nodes (attachment points for leaves) and internodes (space between nodes).

  • Capable of photosynthesis in younger, green stems.

  • Shoots rely on water and nutrients absorbed from the root system.

Components of a Stem

• Nodes: Points where leaves or branches attach.

• Internodes: Segments of the stem between the nodes.

• Leaf scars: Marks left after leaves fall off.

• Lenticels: Structures allowing gas exchange.

• Buds: Growing points that can develop into new shoots or flowers.

• Stems can be woody or soft/herbaceous, with woody stems undergoing secondary growth.

Functions of the Stem

• The primary functions of the stem include:

  • Supporting lateral appendages such as branches, leaves, flowers, and fruits.

  • Conducting water and minerals to shoots.

  • Transporting food throughout the plant.

  • Storage of carbohydrates and water.

  • Positioning leaves for optimal photosynthesis.

Morphology of Buds

• Buds are undeveloped tissues that can produce new stems and leaves.

• There are different types of buds:

  • Vegetative Buds: Develop into branches.

  • Apical Buds: Located at the apex of the stem.

  • Axillary Buds: Found in the axils of leaves.

  • Floral Buds: Develop into flowers.

Leaves

General Structure

• The leaf is critical to a plant's ability to perform photosynthesis. Key characteristics include:

  • Flattened blade (lamina) and a stalk (petiole).

  • Wide variability in size, shape, and color among different plants.

Parts of a Leaf

• Leaf Base: Expanded area where the leaf attaches to the stem.

• Petiole: Stalk connecting the blade to the stem.

• Lamina: The broad and flattened part of the leaf.

• Stipules: Small appendages that develop at the base of the petiole.

Leaf Structure and Functions

• Leaves serve vital functions:

  • Photosynthesis: Converts light energy into chemical energy.

  • Transpiration: Evaporation of water from leaves.

  • Gas Exchange: Absorption of O2 for respiration and CO2 for photosynthesis.

  • Guttation: Removal of excess water from leaf surfaces.

Leaf Venation Types

• Net Venation: Veins branch into a network (typical of dicots).

• Parallel Venation: Veins run parallel to each other (characteristic of monocots).

Types of Leaves

• Simple Leaves: Single, undivided lamina (e.g., Mango, Peepal).

• Compound Leaves: Lamina divided into multiple leaflets.

  • Pinnate Compound: Leaflets present on a common axis (rachis).

  • Palmate Compound: Leaflets attached at a common point.

Phyllotaxy (Leaf Arrangement)

• Phyllotaxy: Arrangement of leaves on the stem.

  • Alternate Phyllotaxy: One leaf arises at each node.

  • Opposite Phyllotaxy: Two leaves arise from each node, can be:

  • Decussate: One pair positioned at right angles to the next.

  • Superposed: Pairs are vertically aligned.

  • Whorled Phyllotaxy: More than two leaves arise from a single node, forming a circle around it.

Conclusion

• Understanding plant morphology is essential for comprehending plant biology, ecological interactions, and agricultural practices.