Flowers are the reproductive structures produced by plants which belong to the group known as Angiosperms, or 'Flowering Plants'.  This group includes an enormous variety of different plants ranging from buttercups and orchids to oak trees and grasses. There are about 250,000 known species.

A flower is basically made up of four concentric rings of structures. There is an outer ring of modified leaves called sepals. These provide protection to the flower before it opens and are usually green. This outer ring is known as the calyx.

Inside the sepals is another ring of modified leaves called petals which are often brightly coloured. This layer is known as the corolla.

Within the corolla are one or more stamens containing pollen, which are the male reproductive structures.

In the very centre of the flower are the female reproductive organs

Flower Anatomy

The Flower:The flower is the reproductive unit of some plants (angiosperms). Parts of the flower include petals, sepals, one or more carpels (the female reproductive organs), and stamens (the male reproductive organs).

The Female Reproductive Organs:The pistil is the collective term for the carpel(s). Each carpel includes an ovary (where the ovules are produced; ovules are the female reproductive cells, the eggs), a style (a tube on top of the ovary), and a stigma (which receives the pollen during fertilization).

The Male Reproductive Organs:Stamens are the male reproductive parts of flowers. A stamen consists of an anther (which produces pollen) and a filament. The pollen consists of the male reproductive cells; they fertilize ovules.

Fertilization:Pollen must fertilize an ovule to produce a viable seed. This process is called pollination, and is often aided by animals like bees, which fly from flower to flower collecting sweet nectar. As they visit flowers, they spread pollen around, depositing it on some stigmas. After a male's pollen grains have landed on the stigma during fertilization, pollen tubes develop within the

style, burrowing down to the ovary, where the sperm fertilizes an ovum (an egg cell), in the ovule. After fertilization, the ovule develops into a seed in the ovary.

Flower Definition

Flowers are the reproductive organs of plants. Flower is the modified vegetative shoot and is meant for sexual reproduction. Flower arises from a modified leaf called bract. It consists of a very short axis on which whorls of different parts of the flower are present. 

Parts of a FlowerFlowers are diverse in gross appearance but the basic parts which make up the flower are basic throughout. Flower is the specialized and modified shoot. The following are the recognized parts of the flower:

Peduncle: Peduncle is the stalk of a flower.

Receptacle : Receptacle is the stem portion, it is found at the base in the center of the flower. The internodes are short and the number of leaves is small. Hence, receptacle is not usually a large part of the flower. 

Sepals : Sepals form the outermost whorl of the floral structure. They are mostly but not always green and are leaf-like in appearance. Sepals are similar to the foliage leaves of the plant. Sepals are collectively known as the Calyx. The major function of the calyx is the protection of flower parts during early development of the flower or the bud. 

Petals

Petals are present above the sepals whorl. Petals are larger than the sepals, they are brightly colored, leaf-like, broad and are thin organs. The petals collectively are known as the Corolla. Corolla is the attractive part of the flower. They provide additional protection and attract insects to facilitate pollination of the flower. The leaf-like organs, the sepals and the petals are together known as the perianth of the flower. They are similar in appearance.

Carpels : Carpels are one or more in number and are located in the upper center of the flower. Collectively the carpels are known as gynoecium. Carpels are made of three parts: Ovary. Style and Stigma. 

Ovary is the structure present at the base of the carpel. It is an enlarged narrow region bearing one or more ovules.

Style is the slender, neck-like portion of the carpel the leads to the ovary. 

Stigma is of variety of shapes and sizes. It present at the tip of the carpel and is sticky to collect pollen grains. 

Stamens

Stamens are located inside the corolla and are leaf-like appearance. Stamens are the male part of the flower and produces pollen. Stamens consists of a filament and an anther. Stamens are collectively called androecium. 

Anther is the sac located at the tip of the filament that contains pollen.

Filament is the stalk that connects to and holds up the anther. 

Nectaries are often associated with flowers and are found at the receptacle, nectaries produce sugary nectar which attracts insects. 

Calyx: Sepals are collectively known as calyx. It forms the outermost whorl of a flower. They are usually green in color and their typical function is protection for the flower in bud stage and also supports the petals when in bloom. Morphologically sepals are modified leaves. 

Corolla

Corolla makes up the second whorl of the flower and it is composed of petals. They are brightly colored, making the corolla conspicuous, and attractive. Petals are also scented in many cases. They help attracting insects for pollination. 

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Bougainvillea

Flowers

Although you'll notice the colorful parts of a bougainvillea plant first, its true flowers are tiny and inconspicuous. Considered a "perfect" flower in botanical terms, the flower contains both the male sexual structure, or stamen, and the female sexual structure, or pistil. Bougainvillea flowers are trumpet-shaped, white or yellow-white, waxy and less than 1 inch long. They typically develop in a triangularly arranged group of three flowers on a single short stem. Two of these three flowers usually open at the same time, with the third opening slightly later.

Seeds

Although bougainvillea flowers contain both male and female components, they are not self-fertile, and need cross-pollination from other bougainvillea plants to produce seeds. The bougainvillea flower makes nectar that attracts butterflies, moths and hummingbirds, which often carry pollen on their bodies, distributing it among nearby plants. The flower's nectar is kept in a structure called a nectary, which is a swollen area at the base of the tubular flower. The nectary has a long, thin neck accessible to these pollinators. When pollen from another plant is deposited on the surface of the flower's pistil, it grows down into the base of the pistil, called its ovary, where fertilization occurs and seeds develop.

Bracts

Although not technically part of the bougainvillea flower, specialized leaves called bracts surround the tiny true flowers. Bracts come in many bright colors, making bougainvillea a strikingly colorful garden plant. Three papery-looking bracts surround each group of three tiny flowers. Each bract has a central vein, with several spider-like, small veins radiating from it. Although the bracts are leaves, they don't photosynthesize the way most leaves do. Instead, their main function is to protect the tiny flowers that they surround and they also help attract pollinating insects and hummingbirds to the plant with their bright colors.