Flowering plants (angiosperms) reproduce sexually through flowers, which are highly modified and specialized reproductive structures.
A flower is not just a decorative part of a plant—it is a modified shoot designed to ensure successful sexual reproduction.
A flower is a modified shoot that bears reproductive organs and is responsible for sexual reproduction in angiosperms.
Why is a flower called a modified shoot?
• It develops from a floral meristem like a vegetative shoot
• Nodes and internodes are highly condensed or suppressed
• Leaves are modified into sepals, petals, stamens, and carpels
A typical flower consists of the following main parts:
1. Pedicel
2. Thalamus (Receptacle)
3. Floral whorls (Calyx, Corolla, Androecium, Gynoecium)
The pedicel is the stalk of the flower.
• Flowers with pedicel → Pedicellate flowers
• Flowers without pedicel → Sessile flowers
The thalamus is the swollen terminal part of the pedicel.
• It bears all four floral whorls
• Its shape and position determine the ovary condition (hypogynous, perigynous, epigynous)
Most flowers consist of four concentric whorls arranged on the thalamus:
1. Calyx
2. Corolla
3. Androecium
4. Gynoecium
Based on their function, floral whorls are classified as:
• Accessory whorls: Calyx and Corolla
• Essential whorls: Androecium and Gynoecium
The calyx is the outermost floral whorl and consists of sepals.
Characteristics of Sepals:
• Usually green in colour
• Leaf-like in appearance
• May be free (polysepalous) or fused (gamosepalous)
Functions of Calyx:
• Protects the flower in bud stage
• May perform photosynthesis
The corolla is the second whorl and consists of petals.
Characteristics of Petals:
• Brightly coloured
• May be scented
• Contain nectar glands
Functions of Corolla:
• Attracts pollinators such as insects, birds, and bats
• Helps in pollination
In some flowers, sepals and petals are indistinguishable. Such structures are called tepals, and collectively they form the perianth.
• Commonly found in monocots (e.g., lily)
The androecium is the male reproductive part of the flower.
Structure of a Stamen
Each stamen consists of:
1. Filament – long, slender stalk
2. Anther – terminal fertile part
Anther Structure (Brief)
• Usually bilobed
• Each lobe contains two microsporangia
• Microsporangia produce pollen grains
Based on Fusion of Filaments:
• Monadelphous – stamens united into one bundle (China rose)
• Diadelphous – stamens united into two bundles (Pea)
• Polyadelphous – stamens united into many bundles (Citrus)
Based on Fusion of Anthers:
• Syngenesious – anthers fused, filaments free (Sunflower)
The gynoecium is the female reproductive part of the flower, also called the pistil.
Structure of Pistil
1. Stigma – receives pollen grains
2. Style – elongated stalk
3. Ovary – basal swollen part
The ovary contains one or more ovules, which develop into seeds after fertilization.
• Bisexual flowers – contain both androecium and gynoecium (Mustard, Hibiscus)
• Unisexual flowers – contain either androecium or gynoecium (Papaya, Cucumber)
Actinomorphic (Radial Symmetry)
• Can be divided into two equal halves in any plane
• Example: Mustard, Datura
Zygomorphic (Bilateral Symmetry)
• Can be divided into two equal halves only in one plane
• Example: Pea
Asymmetric
• No plane of symmetry
Hypogynous Flower
• Ovary is superior
• Other floral parts arise below the ovary
• Example: Mustard, Brinjal
Perigynous Flower
• Ovary is half-inferior
• Floral parts arise at the same level
• Example: Rose
Epigynous Flower
• Ovary is inferior
• Floral parts arise above the ovary
• Example: Sunflower, Guava
Placentation refers to the arrangement of ovules inside the ovary.
Types of Placentation:
• Marginal – Pea
• Axile – Tomato, Lemon
• Parietal – Mustard
• Free central – Dianthus
• Basal – Sunflower
Aestivation is the arrangement of sepals or petals in a floral bud.
Types of Aestivation:
• Valvate – margins touch but do not overlap
• Twisted – each petal overlaps the next
• Imbricate – irregular overlapping
• Vexillary – characteristic of Papilionaceae (pea family)
• Bracteate flower – flower with bract
• Ebracteate flower – flower without bract
• Dichlamydeous – both calyx and corolla present
• Monochlamydeous – only one whorl present
• Achlamydeous – no calyx or corolla
• Essential for understanding plant reproduction
• Frequently asked in NEET and CBSE exams
• Helps in identifying plant families
• Foundation for topics like pollination, fertilization, and seed development
The structure of a flower is a beautifully coordinated system designed for sexual reproduction in flowering plants. Each part has a specific role, from protection and attraction to gamete production and fertilization. A clear understanding of flower structure not only helps in exams but also builds strong conceptual knowledge in plant biology.