Morphology of Flowering Plants 

The morphology refers to the study and description of the physical form and external structure of plants. Flowering plants are the most diverse and widespread group of plants but they are all characterized by presence of roots, stems, leaves, flowers and fruits. The morphological study of flowering plants includes several key components. 

1.0Flowering Plants

Flowering plants, also known as angiosperms, are the most diverse group of land plants, with approximately 64 orders, 416 families, over 13,000 known genera, and about 300,000 species. Flowering plants are cosmopolitan, occupying a wide range of habitats on land, in fresh water and in the sea. The underground part of the flowering plant is the root system while the portion above the ground forms the shoot system. 

2.0The Root 

Root usually develops from the radicle of seed, lacking nodes and internodes. These roots are typically non-green and subterranean, exhibiting positive geotropism while showing negative phototropism. There are three types of root system. 

1. Tap Root System 

In many dicotyledonous (dicot) plants, the radical's direct elongation forms the primary root, which then gives rise to lateral roots across various orders, known as secondary, tertiary, and so on. This entire structure, comprising the primary root and its lateral branches, is called the tap root system. An example of this is the mustard plant.

2. Fibrous Root System 

Typical of monocotyledonous (monocot) plants, the primary root has a brief lifespan and is superseded by a multitude of roots. These roots arise from the stem's base, creating a network that forms the fibrous root system. A common example of this root type is found in the wheat plant.

3. Adventitious Root System  

In certain plants, such as grass, Monstera, and the banyan tree, roots emerge from plant parts other than the radicle. These roots are termed adventitious roots. 

Functions of the Root System:

Absorption of water and minerals, provide a proper anchorage to the plant parts, storage of reserve food material (Carrot, radish, turnip, sweet potato and Asparagus) and synthesis of PGR (plant growth regulators).

Region of Root:

Root Cap: Protects the root apex during soil penetration.

Meristematic Region: Just above the root cap, where cells divide actively.

Elongation Region: Cells elongate, aiding root length growth.

Maturation Region: Cells differentiate and mature; root hairs form here to absorb water and minerals.

Modification of Root 

1. Modified Roots for Support

Prop Roots: Example - Banyan tree roots hanging and supporting the tree.

Stilt Roots: Example - Roots emerging from the lower nodes of maize and sugarcane stems for support.

2. Modified Roots for Storage of Food

Tap Roots: Example - Carrot and turnip roots become swollen and store food.

Adventitious Roots: Example - Sweet potato roots swell and store food.

3. Modified Roots for Respiration

Pneumatophores: Example - Roots of Rhizophora (mangrove species) growing in swampy areas; these roots protrude above the ground and grow vertically upwards to facilitate oxygen intake for respiration.

3.0The Stem 

The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The region of the stem where leaves are born are called nodes while internodes are the portions between two nodes. The stem bears buds, which may be terminal or axillary. Stem is generally green when young and later often becomes woody and dark brown. Stem shows negatively geotropic growth. 

Function of Stem:

• The main function of the stem is spreading out branches bearing leaves, flowers and fruits. 
• It conducts water, minerals and photosynthates.
• In some plants, stems perform the function of storage of food, support, protection and of vegetative propagation.

Modification of Stem:

1. Underground Modifications

• Tuber: Swollen, stores food. E.g., Potato.
• Rhizome: Horizontal, for storage/perennation. E.g., Ginger.
• Corm: Condensed, vertical. E.g., Colocasia.
• Bulb: Reduced stem, stores food. E.g., Onion.

2. Sub-Aerial Modifications

• Runner/Stolon: Spread, form new plants. E.g., Strawberry, Jasmine.
• Sucker: Emerges above ground from below. E.g., Mint, Banana.
• Offset: Aquatic, with leaves/roots. E.g., Pistia.

3. Aerial Modifications

• Tendril: For climbing. E.g., Grapes.
• Thorn: For protection. E.g., Bougainvillea.
• Phylloclade: Photosynthesis, spiny leaves. E.g., Opuntia.

4.0The Leaf

Leaves are crucial vegetative structures emerging laterally from the stem at nodes, typically featuring a flattened shape for efficient photosynthesis. They arise from shoot apical meristems, displaying acropetal arrangement, and comprise three principal components:

1. Leaf Base (Hypopodium): This part attaches the leaf to the stem. In monocots, it forms a sheath around the stem, either partially or fully. Some legumes have a swollen leaf base, termed pulvinus.
2. Petiole (Mesopodium): The stalk linking the lamina (leaf blade) to the stem or branch. Leaves with petioles are petiolate; without petioles, they are sessile. Variations include swollen petioles in Eichhornia and winged petioles in Citrus, aiding in light exposure and air flow around the leaf.
3. Lamina (Epipodium): The wide, green, flattened part of the leaf dedicated to photosynthesis and transpiration.

Modification of Leaf:

Leaf modifications transform leaves into specialised structures, serving unique functions beyond photosynthesis:

• Leaf Tendril: Entire leaf or part becomes a wiry structure for climbing. Example: Wild pea (Lathyrus aphaca).
• Leaf Spine: Leaves harden into sharp spines for protection. Examples: Opuntia, Cacti.
• Leaf Pitcher: Leaves morph into pitcher shapes for trapping insects or storing water. Examples: Nepenthes (insectivorous), Dischidia (non-insectivorous).
• Leaf Bladder: Leaves form bladder-like structures for trapping small organisms. Example: Utricularia (bladderwort).
• Phyllode: Petioles widen and assume leaf functions, including photosynthesis. Examples: Australian acacia, Parkinsonia.
• Leaflet Tendril: Part of the leaf (leaflet) adapts into a tendril for support. Examples: Garden pea (Pisum sativum), Sweet pea (Lathyrus odoratus).

5.0Flower

A flower is a modified shoot where in the shoot apical meristem changes to floral meristem. Internodes do not elongate and the axis gets condensed. When a shoot tip transforms into a flower, it is always solitary.

Generally flowers have a short or long stalk which is called pedicel. The upper part of the pedicel is swollen, which is called thalamus. Floral leaves are present on it.

There are 4 types of floral leaves.

• Calyx (whorl of Sepals) 
• Corolla (whorl of  Petals)
• Androecium (whorl of Stamens)
• Gynoecium (whorl of pistils or carpels) 

6.0The Fruits 

The fruit is the characteristic feature of the flowering plants. It is the mature or ripened ovary, developed after fertilisation.

If a fruit is formed without fertilisation of the ovary, it is called a parthenocarpic fruit. In some fruits like grapes, banana seeds are not found and such types of fruits are called parthenocarpic or seedless fruits. Parthenocarpy can be induced through the application of growth hormones. Generally the ovary wall changes into pericarp. This pericarp may be thick and fleshy or thick and hard or thin and soft.

In fleshy fruits pericarp (fruit wall) is made up of 3 layers :-

Outermost layer      = Epicarp

Middle layer            = Mesocarp

Innermost layer       = Endocarp

Learn more: Fruits

7.0The Seed 

The ovules after fertilisation, develop into seeds. A seed is made up of a seed coat and an embryo. The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea).

Types of Seeds

Based on Cotyledon Number

Monocotyledonous Seeds (Monocots)

• Have one cotyledon (seed leaf).
• Examples include grains like wheat, rice, and corn.

Dicotyledonous Seeds (Dicots)

• Contain two cotyledons.
• Examples include beans, peas, and almonds.

Based on Endosperm Presence

Endospermic Seeds (Albuminous Seeds)

• Retain endosperm at maturity, providing nutrition to the germinating seed.
• Examples: Most monocots, such as wheat and corn, and some dicots like castor.

Non-Endospermic Seeds (Exalbuminous Seeds)

• Consume the endosperm during development, and the cotyledons provide nutrition to the germinating seed.
• Examples: Most dicots, such as peas and beans.