CHAPTER 5 MORPHOLOGY OF FLOWERING PLANT

Morphology

Morphology is the branch of biological science that deals with the study of form, size, colour, structure and relative position of various parts of organisms.

CHAPTER 5 MORPHOLOGY OF FLOWERING PLANT

Morphology Flowering Plants

The plant body consists of a main axis, which may be branched or unbranched bearing lateral appendages.

The flower

Flower is the reproductive part of angiospermic plants for sexual means of reproduction.

A typical flower has four whorls arranged on a swollen end of stalk or pedicel called thalamus. They are Calyx, Corolla, Androecium and Gynoecium.

When a flower has both androecium and gynoecium, the flower is called bisexual and flower having either androecium or gynoecium only is called unisexual.

When flower can be divided into two equal radial halves in any radii passing through center the symmetry of flower is called actinomorphic (radial symmetry) as in Mustard, Datura, and Chili.

When flower can be divided into two similar parts only in one vertical plane it is zygomorphic as in Pea, Gulmohar, Cassia etc.

When Floral appendages are in multiple of 3, 4 or 5 they are called trimerous, tetramerous and pentamerous respectively. Flower with bracts are called bracteates and without it ebracteate.

Based on the position of ovary with respect to other floral part on thalamus, flowers are of following types:

• Hypogynous flower:

• Ovary occupies the highest position. The ovary in such case is called superior. E.g., Mustard, brinjal and china rose.

• Perigynous flowers:

• If the gynoecium is situated at the center and other parts are on the rim at same height. Ovary is called half-inferior.

• Epigynous flowers:

• The margin of thalamus grows to completely cover the ovary. Ovary is said to be inferior.

Calyx

Calyx is the outermost whorl of the flower; its members are called sepals. They are generally green and leafy; protect the flower in bud stage. It may be gamosepalous (sepals united) or polysepalous (sepals free).

Corolla

consists of petals, brightly colored to attract the insects for pollination. They may be gamopetalous or polypetalous.

• The mode of arrangement of sepals or petals in floral bud with respect to the other members of same whorl is called aestivation. In valvate, the whorls of sepals or petals touch each other as in Calotropis. In Twisted aestivation, the whorls overlap each other as in China rose.
• In Imbricate aestivation, margin overlap each other but not in particular fashion as in Gulmohur.
• In pea and bean flowers, there are five petals- the largest (standard) overlaps the two lateral petals (wings) which in turn overlap two smallest anterior petals (keel). This type of aestivation is known as vexillary or papilionaceous.
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The Androecium

• Androecium represent the male reproductive parts of flower, consists of stamens. Each stamen consists of filament and anther. Pollen grains are produced in pollen sac. Sterile stamen is called Stemenode.
• When stamens are attached with petals it is called epipetalous (Brinjal). Stamen may be free (polyandrous) or may be united in one bundle (monoadelphous), two bundles (diadelphous), more than two (polyadelphous).

Placentation

The arrangement of ovules within the ovary is called placentation.

The Gynoecium

• Female reproductive part of flower consists of one or more carpels. Each carpel is made up of stigma style and ovary.
• When more than one carpel is present, it may be free (apocarpous) as in lotus and rose or fused together (syncarpous) as in mustard and tomato.
• After fertilization, ovules change into seeds and ovary mature into fruits.

 Flowers can either be:

• Complete
• Incomplete

A complete flower is the one that consists of sepals, petals, stamens and pistil. On the contrary, an incomplete flower is the one that lacks one or more of these structures.

 A complete flower consists of two different parts

• Vegetative Part
• Reproductive Part

 Vegetative Parts of a Flower

 Petals:

This is a bright-colored part that attracts bees, insects, and birds. Color of petals varies from plant to plant; some are bright while some are pale colored. Thus, petals help us to differentiate one flower from another.

Sepals:

Sepal is the green-colored part beneath the petals to protect rising buds. Some flowers have fused petals-sepals while a few have separated petals-sepals.

Reproductive Parts of a Flower

Stamen:

This is the male reproductive organ and is also known as Androecium. It consists of two parts namely: anther and filaments. the anther is a yellowish, sac-like structure, involved in producing and storing the pollens the filament is a slender, threadlike object, which functions by supporting the anther.

Pistil:

This is the innermost part and the female reproductive organ of a flower which comprises three parts -stigma, style and ovary. This is collectively known as the pistil.

Stigma:

It is the topmost part or receptive tip of carpels in the gynoecium of a flower.

Style:

It is the long tube-like slender stalk that connects stigma and the ovary.

Ovary:

It is the ductless reproductive gland that holds a lot of ovules. It is the part of the plant where the seed formation takes place.

Carpels:

The carpel is the fourth whorl of the flower present in the center. The carpels contain the pistil, the female reproductive part of the flower. It comprises the ovary, style, and stigma. The egg or the ovule is present in the ovary. After fertilization, sometimes the ovary turns into the fruit to keep the seed. At the top of the ovary is a vertical structure called style that supports the stigma. The dispersed pollens stick to the stigma and travel down to the ovary through the style.

Functions Of Flower

Gametophytes develop in the flowers.

The flowers can produce diaspores without fertilization.

After fertilization, the ovary of the flower develops into a fruit containing a seed.

The most important function of flowers is reproduction. They help in the union of male and female gametes.

Flowers provide nectar to certain birds and insects, which in turn help in the transfer of pollen from one flower to the other.

Flowers may promote selfing, i.e., the union of sperms and eggs from the same flower, or cross-fertilization, i.e., the union of sperms and eggs from different flowers.

Semi -Technical description of a typical flowering plant

The plant is described beginning with its habit, vegetative characters – roots, stem and leaves and then floral characters inflorescence and flower parts.

The floral formula is represented by some symbols. In the floral formula, Br stands for bracteate K stands for calyx, C for corolla, P for perianth, A for androecium and G for Gynoecium. Fusion is indicated by enclosing the figure within bracket and adhesion by a line drawn above the symbols of the floral parts.

Family Fabaceae

This family was earlier known as Papilionoideae. Herbs, shrubs or tree root with root nodules. Pinnately compound leaves with reticulate venation.

Economic importance

Plants belonging to this family are sources of pulses like Gram, Arhar, Bean. Pea etc. and edible oils like groundnut, soybean, etc.

Family Solanaceae

Plant body herbs or shrubs, rarely small trees, commonly known as potato family. Leaves simple or pinnately compound. Reticulate venation.

Many of them are source of food (potato, tomato, Brinjal etc.), spices (Chilli) etc.

Family Liliaceae

• Commonly known as Lily family. Monocots, perennial herbs. Leaves alternate with parallel venation.
• Underground bulbs, corms or rhizomes.
• Flower bisexual, actinomorphic, sepals and petals are absent, having perianth.
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It includes ornamental plants (Tulip), Medicine (aloe) and vegetable (colchicine).

Pollination

Pollination is the process in which the pollens are transferred from anther to stigma. The process of pollination can occur through a different medium.

 

The fruit

Mature and ripened ovary developed after fertilisation is fruit. If a fruit is formed without fertilisation of ovary it is called parthenocarpic fruit.

Fruit consists of seeds and pericarp. Thick and fleshy pericarp is three layered called epicarp, mesocarp

Dicotyledonous Seeds

Dicotyledonous Seed is made up of a seed coat and an embryo. Embryo is made up of embryonal axis, radicle and cotyledons.

Seed coat has two layers outer testa and inner tegmen. Hilum is scar through which seed is attached to the ovary. Small pore above the hilum is called micropyle.

Monocotyledonous seeds

In monocotyledonous seed, outer covering of endosperm separate the embryo by a proteinous layer called aleurone layer. Single cotyledon is called as scutellum having a short axis bearing Plumule and radicle. Plumule and radicle are closed inside sheaths called as coleoptile and coleorhiza respectively.

The Leaf 

Leaves originate from shoot apical meristem and are arranged in an acropetal order a typical leaf consists of three parts – Leaf base, Petiole, Lamina. Leaf is attached with stem by Leaf Base which may bear two small leaf like structure called stipule.

Simple Leaves

A leaf having a single or undivided lamina is called Simple leaf. The incisions do not touch the mid rib. Example- Mango, Guava etc.

Compound leaves

When the incision of lamina reach up to the midrib and breaking it into a number of leaflets, it is called Compound leaves.

Pinnately compound leaves:

In a Pinnately compound leaves, a number of leaflets are present on common axis called rachis. Example- Neem.

Palmately compound leaves:

In Palmately compound leaves, the leaflets are attached at common point. Example- Silk cotton.

Venation

The arrangement of veins and veinlets in the lamina of leaf.

Types of Venation:

 Reticulate Venation:

Veinlets form a network as in leaves of dicotyledonous plants (China rose, peepal).

 Parallel Venation:

Veins are parallel to each other as in leaves of monocotyledonous plants (grass, maize, sugarcane).

The Stem

Stem is the aerial part of the plant and develops from plumule of the embryo. It bears nodes and internodes.

Functions of stem:

Exposure of leaves, conduction of water and minerals, translocation of food, exposure of flowers and fruits.

Modification of stems:

• Underground stem of potato, ginger and turmeric are modified to store food. They also act as organ of perennation in unfavorable conditions.
• Stem tendril help plants to climb as in cucumber, pumpkins, and grapes.
• Axillary buds of stem may modify into woody, straight and pointed thorns as in Citrus and Bougainvillea.
• Plants of arid regions modify their stem to flatted (Opuntia), fleshy cylindrical (Euphorbia) having chlorophyll for photosynthesis.

The Root

In plants, root is the non-green (due to absence of chlorophyll), cylindrical and descending part that normally grows downwards into the soil. It does not bear leaves, buds and not distinguished into nodes and inter nodes.

Functions of Roots:

The major functions of roots are as follows:

• Fixation Root provides fixation to the plants with soil.
• Absorption Roots absorb water and minerals from the soil and provide it to all parts of the body.
• Storage Roots of many plants store food for the use of other plant parts and for animals.
• Aeration Plants growing in waterlogged soil or marshy areas have special roots, i.e., pneumatophores for respiration.
• Conduction Roots transport water and minerals in upward direction for the uses of stems and leaves.

The main axis is divided into two parts:

• Root system:

• The underground root system develops from the radicle embryo and helps in fixation of the plant as well as absorption of water and minerals.

• Shoot system:

• The shoot system is the aerial part of the plant, which is found above the root and ground level. The shoot system includes the stem, leaves, bud, flower, fruits and the seeds. Shoot system is one of the important systems of a plant.

Main functions of root system:

• Absorption of water and minerals from the soil.
• Provides anchorage to plant parts.
• Stores reserve food material and synthesizes plant growth regulators.

Various types of root:

• Tap root:

• Originates from radicle. Dicotyledonous plants e.g., mustard, gram, mango.

• Fibrous root:

• Originates from base of the stem. Monocotyledonous plants e.g., wheat, paddy.

• Adventitious root:

• Originates from parts of the plant other than radicle. Banyan tree (Prop roots) Maize (Stilt roots).

Regions of Roots:

• The apex of root is covered by a thimble like structure called root cap, it protect the tender apex of root while making way through soil.
• Above the root cap is region of meristematic activity having small cells with dense cytoplasm.
• The part above the region of meristematic activity is region of elongation where cells under go elongation and enlargement to increase the length of root.
• Region of maturation contain root hairs that help in absorption of water and minerals.
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Modification of roots:

Roots are modified for storage, nitrogen fixation, aeration and support.

• Tap root of carrot, turnip and adventitious root of sweet potato get swollen to store food.
• Prop root of Banyan and Stilt root of maize and sugarcane have supporting root coming out from lower node of stems.
• In Rhizophora, Pneumatophores help to get oxygen for respiration as it grows in swampy areas.
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Inflorescence

A flower is a significant part of a plant tailored for reproduction. In addition, it is an essential part of the bouquet, decorations, celebrations, garden, rituals, etc. Among different parts of a plant, the flower is the most attractive part due to its beauty and fragrance.

Racemose Inflorescence

In this type of inflorescence, the flowers branch laterally on the floral axis. Here the floral axis keeps on growing and the flowers develop in an acropetal pattern.

Cymose Inflorescence

In this type of inflorescence, the flower is the terminating point of each floral axis. In Cymose inflorescence, flowers follow the basipetal pattern of growth.

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