Flowers do not just add color and beauty to a plant, but are vital for reproduction. By creating pollen and attracting insects and other pollinators, the different parts of the flower facilitate transportation of pollen between plants. This helps in development of a new generation of plants.
Here is a guide to the various parts of the flower and their functions:
Four main parts of the flower
There are four main parts in most flowers that include petals, sepals, stamens and pistil. Sepals are the flower’s outer parts that are leaf-like and enclose a bud when it is developing. Petals are the flower parts that are conspicuously colored. Stamens are the male parts of flowers while pistils or carpels are its female parts.
Complete and incomplete flowers
Flowers that have all these four parts are called complete flowers. Not all plant species produce complete flowers and the flowers that do not have all four parts are called incomplete flowers.
Flowers that contain gynoecium and androecium are also called perfect, hermaphrodites or androgynous. Incomplete flowers can be of two types, staminate flowers that only contain an androecium and carpellate flowers with only a gynoecium.
The four whorls
The parts of a flower are also categorized based on ‘whorls’ which refer to an arrangement of petals, sepals, leaves or stamen that wrap around the stalk or stem and radiate outward from the single point on the stem.
The four whorls are calyx, corolla, androecium and gynoecium. Calyx is the outermost whorl and is composed of sepals while corolla, the second whorl, is composed of petals. Calyx and corolla together form the perianth. The third whorl of androecium consists of the male reproductive parts (stamen) while gynoecium, the innermost whorls, contains the female part of the flower or the carpels.
Calyx and corolla are known as the vegetatitive parts of the flower while the androecium and gynoecium are the reproductive parts.
Calyx and corolla: The outermost whorl has green, leafy structured called sepals. The calyx protects the unopened bud. The sepals typically fall off after the bud develops into a flower. In some flowers, the calyx or sepals can persist till the stage the fruit appears, for instance, in plant species such as tomato and brinjal.
The second whorl with petals is typically brightly colored and known as corolla collectively. The number of petals and sepals a flower has can vary based on whether the plant is a dicot or a monocot. Petals protect the essential whorls during the bud stage while also helping in attracting insects for pollination.
Flowering plants are traditionally divided into monocots and dicots. Monocots and dicots differ from each other on the basis of seeds, leaves, flowers and roots. The seed of a monocot contains only one cotyledon that stores food for the new plant and germinates into leaves while a dicot has two cotyledons. Flower parts in a monocot are three or in multiples of three whereas in a dicot, they can be four or five or in multiples of either four or five.
Androecium- The third whorl is the androecium that contains the male reproductive parts. The different parts of the androecium include:
- Anther: The anther is a sac-like, yellowish structure in the flower and is involved in production and storage of pollens. The anthers are supported by the long filaments and rise high up from the center of the flower. The number of anthers each flower species have can depend on the type of flowering species. However, most flower species have five or six anthers circling the flower’s center. Botanists term the anthers and filaments together as stamen.
- Filament -This is a thin and long structure that helps anchor the anther to the flower’s base. The filaments can be seen when the flower opens up which look like stems in the flower itself. The anther sits on top of the filament. Filaments have the main function of ensuring nutrients reach the anther where the pollen develops. While the filaments are short when the flower is developing, they lengthen after the flower fully opens, facilitating access to pollinating agents (such as bees ) and to the anthers.
- Microsporangia – These are located within the anther and act like pollen sacs where microspheres or pollen are produced. The pollen or microspheres produce male gametophytes that develop further into sperm cells. These sperm cells fuse with egg cells from the ovary of the flower when fertilized.
Gynoecium- The gynoecium is the innermost whorl of the flower containing the female reproductive parts.
The carpel: The gynoecium is made up of one or more carpels. The carpel is composed of different parts including:
- Stigma: This is the topmost part of carpels
- Style: This is a slender, tube-like, long stalk that connects the stigma to the ovary.
- Ovary: Located at the base of the carpel, the ovary is a ductless reproductive gland containing a lot of ovules. Seed formation occurs in the ovary.
- Ovules: The ovule is within the ovary and has a nucleus (also called megasporangium) with a protective layer ( integuments). The nucleus develops into the seed while the integuments become the seed coat when the flower is fertilized.
The other parts of a flower include the peduncle, which is the stalk to which the flower is attached, and the receptacle, which is the part on the flower stalk where all the other flower parts are attached.
The main function of the reproductive parts of the flower
The plant is able to reproduce because of the egg (in the ovules) and sperm (in the anther) of flowers.
The pollen in the anthers contain the sperm required for reproduction. The long filaments support the anthers from the flower’s center to boost the chances of a visiting pollinator coming in contact with the anther and collecting the pollen. When the pollinator goes to another plant, the pollen on its body falls on the flower’s female organs. The pollen sends the sperm into the ovary of the flower to fertilize the egg. All stamens, however, do not bear fertile anthers always. In specific plant species, four stamens out of the ten are sterile.
If both female and male flowers are contained in the same plant, the plant species is known as monoecious that means “one home.” Examples for this species are corn and pea plants. Species that have the female and male parts in separate plants are called dioecious with examples being Cannabis and papaya.