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BIOLOGY MORPHOLOGY OF FLOWERING PLANTS

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Morphology of Flowering Plants

Morphology is the branch of biology which deals with form, size, structure and relative position of

various organs of a living organism. A typical flowering plant has two main parts: o Root system o Shoot system

The Root

The root is the non-green part of the plant which grows below the ground.

Types of Root Systems

Tap Root System Adventitious Root System Fibrous Root System The radicle of the seed elongates and grows to form the primary root or tap root. The primary root is short lived. Roots develop from parts of the plant other than the radicle. The primary root gives out several lateral branches which are called secondary and tertiary roots. The primary root gets replaced by many roots which originate from the base the stem. These are clusters of slender, adventitious roots. The primary root with its lateral branches forms the tap root system. These roots form the adventitious root system. These roots form a fibrous root system. Tap roots penetrate deep into the soil. Adventitious roots do not penetrate deep into the soil. Fibrous roots do not penetrate deep into the soil. Example: Mustard plant Examples: Bryophyllum Examples: Maize

Regions of the Root

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Modifications of Roots

Storage Roots Roots which store food become thick, swollen and fleshy. Carrot and radish are modified tap roots which store food. Sweet potato is a modified adventitious root which stores food. Roots for Support The roots are modified to provide additional support to the plant. In sugarcane, stilt roots arise from the nodes of the stem and support the main axis of the plant. In Banyan tree, prop roots arise from stem and grow downwards in the soil to provide mechanical support to the tree. Respiratory Roots The roots of plants which grow in marshy areas are unable to obtain air from the soil. Such plants develop roots from tap roots which grow above the ground.

They are called pneumatophores.

Example: Avicennia Nodulated Roots Secondary roots bear small swellings called nodules. Nodules contain nitrogen-fixing bacteria Rhizobium which fix nitrogen for plants.

Roots Modified for

Vital Functions

Epiphytic roots help in absorption and storage of water. Example: Orchids Assimilatory roots perform photosynthesis. Example: Tinospora Parasitic roots penetrate the host tissues to absorb food material. Example:

Cuscuta

Floating roots help aquatic plants to float on water. Example: Jussiaea It is a thimble-or cap-like structure which covers the tender apex of the root.

Root Cap

The cells are small, thin-walled with dense protoplasm. Cells of this region divide rapidly and add new cells lengthwise.

Region of Meristematic Activity

This zone is proximal to the region of meristematic activity. The cells do not divide but elongate and enlarge.

Region of Elongation

The cells of this region differentiate into permanent tissues depending on the function they have to perform. Some epidermal cells of this regiion form fine delicate thread-like root hair.

Region of Maturation

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The Stem

The stem is the ascending part of the axis bearing leaves, flowers, buds, fruits and branches.

The region on the stem where leaves originate is called the node, while the region between two nodes

is called the internode.

Primary Functions of the Stem

The stem holds leaves and branches and provides mechanical support to the plant.

It conducts water and minerals from the roots to the leaves and other parts, while synthesised food

from the leaves to the other parts of the plant.

Modifications of Stem

Storage Stems Underground stems such as potato, ginger store food. Aerial Stems Stems undergo extreme modifications to perform several special functions. Tendrils are thin, wiry, spirally coiled branches which help plants to climb.

Example: Passiflora

Bulbils are condensed axillary buds which help in vegetative propagation.

Example: Garlic

Thorns are modified axillary buds which protect plants from grazing animals.

Example: Citrus

Phylloclades are green, flattened or cylindrical stems which help in photosynthesis. Example: Cactus Sub-aerial Stems Sub-aerial stems help in vegetative propagation. A runner is a thin, delicate aerial branch. Runners develop adventitious roots from the nodes. Example: Oxalis A stolon develops from underground stems. It projects outwards horizontally. Example: Strawberry An offset is a short, thickened horizontal branch. At the apex, it produces a tuft of leaves above and a cluster of roots below the ground. Example: Pistia

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The Leaf

A leaf is a green, flattened structure which develops at the node of a stem.

Primary Functions of the Stem

Leaves are the main site of photosynthesis in plants. They carry out exchange of gases through stomata. They also carry out transpiration which helps plants in the continuous ascent of sap.

Pars of Typical Leaf

A leaf has three main parts:

Leaf Base: The leaf is attached to the stem at the leaf base. It bears two lateral leaf-like structures

called stipules. Petiole: It is long, thin and flexible. It holds the leaf firm in rain and wind.

Lamina: It is the green expanded part of the leaf. It has a prominent middle vein known as the midrib.

Venation

The arrangement of veins and veinlets in the lamina of leaves is called venation. Reticulate Venation: Branches of veins form a network. Dicotyledons show reticulate venation. Parallel Venation: Veins run parallel to each other. Monocotyledons show parallel venation.

Types of Leaves

The lamina is entire.

If incised, then its incisions do not touch the midrib.

Simple Leaf

The lamina is not continuous.

Incisions of lamina reach the midrib and break the lamina into several leaflets.

Pinnately Compound Leaf:Leaflets are borne on

the main axis called rachis. Palmately Compound Leaf: Leaflets are attached to a common point, i.e. at the tip of the petiole.

Compound Leaf

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Phyllotaxy

Phyllotaxy is the pattern or arrangement of leaves on the stem or branch. Alternate Phyllotaxy: A single leaf arises at each node in an alternate manner.

Opposite Phyllotaxy: A pair of leaves arises at each node and both leaves lie opposite to each other.

Whorled Phyllotaxy: More than two leaves arise at each node and form a whorl.

Modifications of Leaf

Leaf Tendrils Some parts of a leaf or the entire leaf is modified into long, slender, wiry tendrils which coil around the support and help the plant to climb. Example: Pisum sativum Leaf Hooks Some terminal leaflets of compound leaves become stiff, curved hooks which cling to the support and help the plant to climb. Example: Bignonia Leaf Spines Leaves are modified into spines which help plants to reduce transpiration in dry habitats. Example: Yucca Scale Leaves Scale leaves are dry, brownish, membranous leaves. Examples: Onion,

Picther The lamina is modified into a pitcher.

The function of the pitcher is to catch and digest insects. Example: Nepenthes Bladder Segmented leaves are modified into a bladder-like structure which helps plants in trapping insects. Example: Utricularia

The Inflorescence

The arrangement of flowers on the floral axis is called an inflorescence.

Racemose Inflorescence Cymose Inflorescence

The main axis of the flower continues to grow, and hence, the axis bears a number of flowers. The main axis terminates into a flower. The arrangement of flowers is acropetal, i.e. older flowers are at the base and younger ones are towards the apex. The arrangement of flowers is basipetal. Examples: Gulmohar Examples: Datura

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The Flower

The flower is a modified reproductive shoot in angiosperms.

Symmetry of Flower

Actinomorphic Flower: Flower can be divided into two equal radial halves when cut in any radial plane passing through the centre. Example: Datura Zygomorphic Flower: Flower can be divided into two equal halves only in one vertical plane passing through its centre. Example: Gulmohar Asymmetric Flower: Flower cannot be divided into two equal halves in any vertical plane passing through the centre. Example: Canna

Parts of a Flower

Calyx

It is the outermost whorl of the flower. It is made up units called sepals. When the sepals are fused, the calyx is called polysepalous. When the sepals are free, the calyx is called gamosepalous.

Corolla

It is the second whorl of the flower composed of units called petals. When the petals are united, the corolla is called gamopetalous. When the petals are free, the corolla is called polypetalous. Aestivation: o Mode of arrangement of petals or sepals in floral buds with respect to the other members of the whorl is called aestivation. o Valvate aestivation: Sepals or petals touch each other but do not overlap each other. o Twisted aestivation: One margin of the sepal or petal overlaps with the margin of the next sepal or petal.

o Imbricate aestivation: Margins of sepals or petals overlap each other without any definite pattern.

o Vexillary aestivation: The largest petal called the standard overlaps the two lateral petals called

wings which overlap two smallest anterior petals called keel.

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Androecium

The androecium is the third whorl of the flower. It is the male reproductive organ of angiosperms. It is made of stamens. Each stamen is composed of a filament and an anther. A sterile stamen is called staminode Epipetalous stamens: Stamens are united with the petals. Episepalous stamens: Stamens are united with the sepals. Epiphyllous stamens: Stamens are united with the perianth. Monadelphous stamens: Stamens are united in one bundle. Didelphous stamens: Stamens are united in two bundles. Polydelphous stamens: Stamens are united into more than two bundles.

Gynoecium

The gynoecium is the fourth whorl of the flower. It is the female reproductive organ of angiosperms. The gynoecium is made of one or more carpels. Each carpel has three partsstigma, style and ovary. When carpels are free, it is called apocarpous. When carpels are fused, it is called syncarpous.

Placentation

The arrangement of ovules on the placenta inside the ovary is called placentation.

Marginal Placentation: The placenta forms a ridge on the ventral suture (i.e. where the two margins

of the ovary fuse) of the ovary.

Axile Placentation: The ovary is partitioned into two or many chambers. The placenta appears on the

central region where all septa which separate the chambers of the ovary meet. Parietal Placentation: The placenta develops on the inner wall of the ovary.

Free Central Placentation: Ovules are borne on the central axis which is not connected to the ovary

wall. Basal Placentation: Placenta develops at the base of the ovary.

Positions of Floral Parts on the Thalamus

Floral appendages are in multiples of 3 (trimerous), 4 (tetramerous) and 5 (pentamerous).

Flowers with bracts (reduced leaves found at the base of the pedicel) are called bracteate and those

without bracts are called ebracteate. Hypogynous Flower Perigynous Flowers Epigynous Flowers The gynoecium is situated at the highest position. The gynoecium is located in the centre. Margins of the thalamus enclose the ovary completely.

BIOLOGY MORPHOLOGY OF FLOWERING PLANTS

www.topperlearning.com 9 The calyx, corolla and androecium are situated below the gynoecium. Other whorls are located on the rim of the thalamus at the same level of the gynoecium. Other whorls arise above the ovary. Examples: Brinjal Examples: Plum Examples: Cucumber

The Fruit

A true fruit is a mature, ripened ovary. A typical fruit has a wall called pericarp and seeds. The pericarp may be dry or fleshy.

When the pericarp is fleshy, it is differentiated into the outer epicarp, middle mesocarp and

inner endocarp.

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The Seed

After fertilisation, ovules develop into seeds. A typical seed has a seed coat and an embryo. Structures of Monocotyledonous and Dicotyledonous Seeds

Monocotyledonous Seed Dicotyledonous Seed

The embryo has an embryonal axis and a single cotyledon. The cotyledon is also known as scutellum. The embryo has an embryonal axis and two cotyledons. The endosperm is bulky and stores reserve food material. The seed coat has two layersan outer testa and inner tegmen. Aleurone layers separate the endosperm and the embryo. Above the hilum, there is a small pore called micropyle. The plumule and radicle are enclosed in sheaths called coleoptiles and coleorhizae, respectively. Monocotyledonous seeds are endospermic but orchid seeds are non-endospermic. In mature cells, the endosperm is not present and such seeds are called non- endospermous seeds. Example: Maize Examples: Castor seed

BIOLOGY MORPHOLOGY OF FLOWERING PLANTS

www.topperlearning.com 11 Semi-technical Description of a Typical Flowering Plant Various morphological characters are used for the systematic study of different plant families.

All these characters have symbols, and floral formulae are used to describe different families of plants.

Symbol Description

1. Br Bracteate flower

2. K Calyx

3. nK Polysepalous calyx 4. (n)K Gamosepalous calyx

5. C Corolla

6. nC Polypetalous 7. (n)C Gamopetalous

8. P Perianth

9. A Androecium

10. G Gynoecium

11. Male flower 12. Female flower 13. Bisexual flower 14. Actinomorphic flower

15. % or

Zygomorphic flower A floral diagram provides the following information: o Number of floral parts o Arrangement of floral parts o Relation of floral parts with one another

HabitRootsStemLeaves

InflorescenceSexuality of

Flower

Symmetry of

FlowerPosition of Ovary

Floral WhorlsBracts

Conditions of

Calyx, Corolla,

Androecium,

Gynoecium

Placentation

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Floral Formula and Floral Diagram of Mustard

Floral Formulae and Floral Diagrams of Important Families

Family Fabaceae

Plants of this family are trees, shrubs or herbs. Stem: Erect or climber

Leaves: Alternate, pinnately compound or simple, stipulate, leaf base is pulvinate, reticulate venation

Inflorescence: Racemose Flower: Bisexual, zygomorphic Calyx: Five sepals, gamosepalous, imbricate aestivation Corolla: Five petals, polypetalous, papilionaceous, vexillary aestivation Androecium: Ten stamens, diadelphous, dithecous anthers Gynoecium: Ovary superior, monocarpellary (single carpel), unilocular with many ovules, marginal placentation, single style Fruit: Legume, non-endospermic seeds, seeds may be one to many Floral Formula: Floral Diagram:

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Family Solanaceae

Plants of this family are herbs, shrubs and rarely small trees.

Stem: Herbaceous, rarely woody, aerial and erect, cylindrical, branched, solid or hollow, hairy or

glabrous (smooth), underground stem in potato Leaves: Alternate, rarely pinnately compound, exstipulate, reticulate venation. Inflorescence: Solitary, axillary or cymose Flower: Bisexual, actinomorphic Calyx: Five sepals, gamosepalous and persistent, valvate aestivation Corolla: Five petals, gamopetalous, valvate aestivation Androecium: Five stamens, epipetalous, polyandrous

Gynoecium: Ovary superior, bicarpellary, bilocular with many ovules, syncarpous, axile placentation

Fruit: Berry or capsule Floral Formula: Floral Diagram:

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Family Liliaceae

Plants of this family are perennial herbs. Stem: Bulb, corm, rhizome Leaves: Basal, alternate, linear, exstipulate, parallel venation Inflorescence: Solitary or cymose Flower: Bisexual, actinomorphic and trimerous Perianth (Calyx + Corolla): Six tepals (3+3), often united in a tube, valvate aestivation Androecium: Six stamens (3+3), epiphyllous

Gynoecium: Ovary superior, tricarpellary, trilocular with many ovules, syncarpous, axile placentation

Fruit: Capsule, rarely berry, endospermic seeds Floral Formula: Floral Diagram: