Morphology of Flowering Plants | SSC CGL Tier 2 - Study Material, Online Tests, Previous Year PDF Download

Root System Variations

Flowering plants exhibit diverse root systems tailored to their specific needs, reflecting adaptations to their environment. The root system is broadly categorized into three types:

1. Taproot System: Typically observed in dicots such as gram and mustard, the primary root results from the elongation of the radicle during germination. This central root gives rise to secondary and tertiary roots, imparting stability and aiding in nutrient absorption.

2. Fibrous Root System: Predominant in monocotyledons like rice and wheat, this system features a multitude of roots originating from the stem's base. These roots collectively enhance the plant's ability to anchor itself securely in the soil.

3. Adventitious Root System: In some plants, the primary root does not originate from the radicle. Examples include grass, banyan trees, and maize. The development of roots in unconventional locations allows these plants to adapt to diverse ecological niches.

   

Root Modifications for Varied Functions

Roots undergo modifications to serve specific functions crucial for the plant's survival and growth. These modifications include:

• Storage Roots: Taproots, as seen in carrots and turnips, and adventitious roots, such as those in sweet potatoes, serve as nutrient storage organs, ensuring a reserve of essential substances during adverse conditions.

• Supportive Roots: Some plants, like the Banyan tree, employ prop roots arising from branches to provide additional structural support. Stilt roots in maize and sugarcane emerge from lower stem nodes, contributing to stability.

• Aerating Roots: Mangroves in swampy areas deploy pneumatophores—roots that grow upwards above the ground—to facilitate respiration. Notably, species like Rhizophora employ this adaptation.

• Nitrogen Fixation: Leguminous plants form root nodules, fostering a symbiotic relationship with nitrogen-fixing bacteria. This process enhances soil fertility and nutrient availability for the plant.

Stem Characteristics and Modifications

The stem, emerging from the plumule during germination, plays a pivotal role in transporting substances between the roots and leaves. Stem modifications accommodate a range of functions:

Types of Stem Modifications:

1. Underground Stem: Certain plants feature stems modified for subterranean functions. Examples include rhizomes (ginger, banana), tubers (potato), corms (colocasia), and bulbs (garlic, onions).

2. Stem Tendrils: Coiled structures like those in grapes, cucumber, and pumpkin serve as adaptations for climbing. These tendrils provide mechanical support, aiding the plant's ascent.

3. Thorns: Some plants, such as Bougainvillea and citrus, deploy modified axillary buds that transform into pointed thorns. This adaptation acts as a deterrent against grazing animals, offering protection to the plant.

4. Subaerial Weak Stem: Plants with subaerial stems exhibit various adaptations. Offsets (Eichhornia, Pistia), suckers (chrysanthemum, banana, pineapple), runners (grasses, strawberry), and stolons (mint) showcase the diversity in stem structures serving distinct ecological roles.

5. Aerial Modifications: Xerophytic plants demonstrate unique adaptations in aerial stems. Phylloclades in species like Euphorbia and Opuntia undergo complete metamorphosis, becoming fleshy and green. This modification helps in photosynthesis, compensating for reduced or thorn-like leaves that minimize water loss via transpiration.

Leaves: Structure, Types, and Modifications:

Leaves, vital for photosynthesis, undergo modifications that enhance their functionality. Understanding leaf morphology involves exploring:

• Leaf Types: Leaves can be simple or compound, with the arrangement of lobes and incisions determining their classification.

• Leaf Modifications: Various adaptations include tendrils (as in peas), spines (found in xerophytes like cactus), storage leaves (e.g., garlic, onion), and phyllodes, where the petiole transforms into a leaf-like structure (as seen in Acacia).

• Pitcher Leaves: In unique cases, as observed in pitcher plants, leaves are modified to form pitcher-like structures that trap insects, serving as a specialized adaptation.

Inflorescence: Arrangement of Flowers

The arrangement of flowers around the floral axis, termed inflorescence, is a crucial aspect of flowering plant morphology. Two primary types are racemose and cymose inflorescence, each exhibiting variations like raceme, spike, umbel, capitulum, corymb, catkin, spadix, monochasial cyme, dichasial cyme, etc.

Special Inflorescence Types

Certain plant species exhibit unique inflorescence structures:

• Verticillaster: In plants like Ocimum and Salvia, sessile flowers arrange in a dichasial cyme, creating a distinctive pattern.

• Cyathium: Found in the Euphorbia genus, this inflorescence type features an involucre of bracts forming a cup-shaped structure. A single female flower is surrounded by numerous male flowers.

• Hypanthodium: Represented by the fig, hypanthodium inflorescence encompasses both male and female flowers within a cavity, featuring an apical opening called ostiole.

The Flower: Structure, Symmetry, and Types

The flower, a reproductive structure, comprises four whorls: calyx, corolla, androecium, and gynoecium. Understanding flower symmetry, types, and characteristics involves:

• Flower Symmetry: Flowers can be actinomorphic (radially symmetrical) or zygomorphic (divisible into two equal parts in only one vertical plane).

• Flower Types: Based on the number of floral appendages (sepals, petals, stamens, carpels), flowers are classified as trimerous, tetramerous, or pentamerous.

• Floral Parts: The four whorls—calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels)—are attached to the swollen terminal of the pedicel, known as the thalamus.

Types of Flowers

The presence or absence of bracts and the position of the ovary classify flowers into Bracteate or Ebracteate and Hypogynous, Perigynous, or Epigynous types.

Androecium and Gynoecium: Male and Female Reproductive Parts

Understanding the intricate details of the androecium and gynoecium involves exploring the various structures and arrangements:

• Androecium: The male reproductive part consists of stamens, each comprising a filament and anther. Variations include staminode, epipetalous attachment, polyandrous arrangements, and different forms of adhesion, such as monadelphous, diadelphous, and polyadelphous.

• Gynoecium: The female reproductive part encompasses carpels, each comprising a stigma, style, and ovary. Carpels are categorized as apocarpous (e.g., rose) or syncarpous (e.g., tomato).

Placentation: Arrangement of Ovules in the Ovary

Understanding placentation, the specific arrangement of ovules in the ovary, provides insights into the diversity of floral structures. Types of placentation include marginal (e.g., pea), axile (e.g., lemon), parietal (e.g., Argemone), free central (e.g., Primrose), and basal (e.g., marigold, sunflower).

The Fruit: Mature Ovary and Seed Development

As flowers undergo fertilization, the ovary matures into a fruit. Various aspects of fruit development and seed characteristics include:

• Parthenocarpic Fruit: Some fruits, like pineapple, develop without fertilization, resulting in seedless varieties.

• Seed Structure: Seeds, arising from fertilized ovules, consist of a seed coat and an embryo. Dicotyledonous and monocotyledonous seeds exhibit differences in seed coat layers, cotyledon numbers, and endosperm characteristics.

Conclusion: A comprehensive exploration of the morphological features of flowering plants delves into the intricate structures and adaptations that enable these organisms to thrive in diverse environments. From roots and stems to leaves, inflorescence, flowers, fruits, and seeds, each component plays a vital role in the life cycle and ecological success of flowering plants. The intricate interplay of these features showcases the remarkable diversity and complexity within the plant kingdom.