Flower - Parts And Its Function
A flower serves as the reproductive component of a plant, where the development of fruits and seeds takes place. Morphologically speaking, a flower is a significantly condensed and altered shoot specifically designed for the purpose of reproduction.
1.0The Flower : A Modified Shoot
A flower is a specialized reproductive shoot, arising from a condensed stem known as the thalamus. This compact structure supports whorls of green sepals, colored petals, male stamens, and female carpels. Stamens consist of anthers and filaments, while carpels include a stigma, style, and ovary.
In a standard flower, four distinct types of floral leaves are present, organized into four whorls. These floral leaves are positioned on the enlarged upper sections of the flower stalk, known as the pedicel. The swollen upper part of the flower stalk is referred to as the thalamus or torus. Within the thalamus, nodes are found along with significantly reduced internodes. The floral leaves are arranged in whorls on these nodes.
2.0Parts of Flower
Calyx : The calyx forms the outermost whorl of a flower, comprising sepals that are typically green but can sometimes exhibit coloration, such as the petaloid appearance seen in garden nasturtium. In dicotyledons, the usual count of sepals is five, while in monocotyledons, it is typically three. Within a whorl, the sepals may either be distinct and separate (polysepalous condition) or fused together (gamosepalous condition).
Corolla : The corolla is the second whorl inside a flower, and it consists of petals. Petals are usually colorful and serve to attract pollinators such as insects and birds. Petals can also exhibit variations in color, shape, and size, contributing to the overall diversity of flower structures. Within a whorl, the petals may either be distinct and separate (polypetalous condition) or fused together (gamopetalous condition).
Androecium : The Androecium, representing the third and male whorl of the flower, consists of one or more stamens or microsporophylls. Each stamen is composed of the following parts:
- Filament: The lower, thread-like portion of the stamen is known as the filament. It may be absent in certain stamens.
Length of stamens : there may be variation in the length of filaments within a flower.
- Didynamous : - If four stamens are present and out of them two are long and two are short, then it is called didynamous condition. Eg. Lamiaceae/Labiatae family (Salvia)
- Tetradynamous - When there are six stamens and they are arranged in two whorls. In the outer whorl, there are two short stamens while in the inner whorl, there are four long stamens, this condition is called tetradynamous. Eg. Cruciferae family (Mustard, radish, turnip).
- Anther: Positioned at the upper end of the stamen, the anther typically has two lobes (or thecae), although in the Malvaceae family, it may have only one lobe. Each lobe contains two microsporangia. A two-lobed anther is referred to as a dithecous anther, while an anther with a single lobe is termed monothecous. The theca is filled with pollen grains (microspores). The back side of the anther is the part to which the connective is attached, while the opposite side, called the face, usually features longitudinal slits for the dispersal of pollen grains. When the stamens of an androecium are free from one another, then it is a polyandrous condition.
Cohesion of stamens : when the floral parts of similar whorl are fused, then it is called cohesion.
Adhesion of stamens : when the stamen is attached to other parts of the flower, then it is called adhesion of stamen.
Gynoecium: The gynoecium, serving as the female reproductive organ of the flower, is composed of one or more carpels.
- Monocarpellary Condition: In the monocarpellary condition, only one carpel is present in the gynoecium.
- Polycarpellary Condition: In the polycarpellary condition, more than one carpel is present in the gynoecium.
- Apocarpous Condition: In the apocarpous condition, observed in polycarpellary/multicarpellary situations, all the carpels remain distinct and separate. Examples include Lotus, Rose, and Michelia.
- Syncarpous Condition: In the syncarpous condition, seen in polycarpellary/multicarpellary situations, all the carpels are fused together. Examples include Papaver, Hibiscus, Mustard, and Tomato.
The ovary of a flower can be either one-chambered (unilocular) or divided into multiple chambers (bilocular, trilocular, tetralocular, pentalocular, or multilocular), depending on how many compartments or spaces it has inside.
3.0Types of flowers
In many flowers, both stamens and carpels coexist within the same blossom, giving rise to what is known as hermaphrodite or bisexual flowers. Examples of such flowers include China rose, pea, and cotton. On the other hand, certain flowers exhibit the presence of only one of the essential whorls, leading to the classification of unisexual flowers. Examples of unisexual flowers include Cucurbits and Mulberry. Flowers exclusively bearing stamens are termed staminate flowers, while those with only carpels are referred to as pistillate flowers.
In complete flowers, all four whorls—sepals, petals, stamens, and carpels—are present. Examples of complete flowers include Cotton and China rose. Conversely, if a flower lacks any one of the four whorls, it is categorized as incomplete.
4.0On The Basis Of Symmetry
Actinomorphic/Radial/Regular: An actinomorphic flower can be evenly divided into two identical radial halves by any vertical or radial plane passing through its center. Examples include Mustard, Datura, and Chilli.
Zygomorphic/Bilateral: In a zygomorphic flower, it can only be divided into two similar halves by a specific vertical plane. Examples include Pea, Bean, Gulmohur, and Cassia.
Asymmetrical/Irregular: An asymmetrical flower cannot be divided into two similar halves from any vertical plane passing through the center. Example: Canna.
In the context of asymmetrical flowers, the part closer to the mother axis is termed the posterior part, while the part farther from the mother axis is the anterior part of the flower. The floral diagram represents the position of the mother axis in relation to the flower, denoted by a dot on the top of the diagram.
5.0On The Basis Of Insertion Of Floral Leaves
Hypogynous Flower:
- In a hypogynous flower, the gynoecium occupies the highest position, with other parts like petals, sepals, and stamens situated below the ovary.
- The ovary in this condition is superior.
- Examples include Mustard, China Rose, Brinjal, and Mango.
Perigynous Flower:
- In perigynous flowers, the thalamus grows upward, forming a cup-shaped structure. Floral parts attach to the rim of the thalamus, with the gynoecium located at the basal part or in the center. The ovary is considered half-inferior in this condition.
- Examples include Rose, Plum, and Peach.
Epigynous Flower:
- An epigynous flower features a thalamus whose margin grows upward, enclosing the ovary completely and fusing with it. Other floral parts like petals, sepals, and stamens are situated above the ovary.
- The ovary is inferior, while the rest of the floral parts are superior.
- Examples include Guava, Apple, Cucumber, and the ray florets of Sunflower.
Bract : Bract is a reduced leaf found at the base of the pedicel of a flower.
- Bracteate flower - The flower with bract is called bracteate flower.
- Ebracteate flower - Flower without bract is known as an ebracteate flower.
- Involucre - The whorl of bracts is called involucre.
- Spathe - When a large bract completely encloses whole inflorescence, then it is called spathe. Eg. Banana, maize
- Petaloid bract - When the size of bract is greater than the size of flower and it is of various coloured like petals, then it is called petaloid bract. Eg. Bougainvillea.
- Glumes - Small, dry, scaly bracts are called glumes. Eg. Wheat, grass (Gramineae family).
6.0Function of Flowers
- Reproduction: Flowers are the reproductive organs of flowering plants, containing male (stamen) and female (pistil) structures.
- Pollination: Flowers attract pollinators for the transfer of pollen, essential for fertilization and seed production.
- Seed Production: After successful pollination, flowers develop into fruits, protecting and dispersing seeds.
- Attracting Pollinators: Flowers use colors, shapes, and scents to attract specific pollinators, forming a mutualistic relationship.