Flower Structure

Flower Structure

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Do you love flowers? They come in all shapes, sizes, colors, and scents! But not all plants have flowers. Pine and cypress trees, for example, don't have flowers. Flowers are only found in angiosperms, which are also known as flowering plants. Flowers are involved in plant reproduction, producing the eggs and sperm of the plant, and are the site of sexual reproduction. They also attract pollinators, which transfer the sperm between flowers. In this article, we'll explore the structure of a flower, its components, and how flower diversity is related to their function in plant reproduction.

Flower Structure and Function

A flower is the sexual reproductive structure of angiosperms, which are plants commonly known as flowering plants. Flowering plants are part of the clade Angiospermae, which comes from the Greek words “angeion” (vessel) and “sperma” (sperm or seed). These plants have flowers, as well as ovules that are enclosed by an ovary and become seeds that are enclosed in a fruit.

Angiosperms are one of two groups of plants that produce seeds, the other being gymnosperms. Gymnosperms (from the Greek “gymnos” meaning naked and “sperma”) produce seeds, but they are said to be “naked” because they are not enclosed by a fruit. This is because the ovule is not contained by an ovary either. Gymnosperms appeared earlier than angiosperms in plant evolution and have cones formed by scales, with ovules developing on the surface of the scales. Common gymnosperms are pines, cypresses, and cycads. There are also a few gymnosperms (phylum Gnetophyta) that have cones that look like groups of small flowers, but they are not real flowers as they are not angiosperms.

Flowers come in a great variety of sizes, shapes, and colors. They can be single flowers or in groups called inflorescences. Flowers are part of the plant shoot system, which includes non-reproductive leaves, stems, and reproductive flowers. They develop from a stalk called a peduncle. In inflorescences, each flower has a pedicel that attaches them to the main axis. The tip of the peduncle or pedicel is the receptacle, which contains the flower parts.

Tulips, roses, and magnolias are examples of relatively big individual flowers. Snapdragons and lilac are inflorescences. Sunflowers, on the other hand, look like big individual flowers, but they are actually a type of inflorescence. Sunflowers, daisies, dandelions, and many others belong to the Asteraceae family, in which the floral receptacle contains numerous tiny flowers. The flowers at the border that look like yellow petals are small, incomplete, and sterile flowers (they do not have stamens or pistils). These surround hundreds of smaller flowers in the center containing reproductive components. Additionally, the tiny flowers develop on a big receptacle and do not have individual pedicels.

Flower diversity. From left to right: a rose develops as an individual flower; the next three images show different types of inflorescences

Flowers come in all shapes, sizes, and colors, but their function is always the same: sexual reproduction of the plant. Flowers have structures that carry the plant's gametes (eggs and sperm), which are the sexual reproductive cells. In this article, we'll explore the four main floral structures: sepals, petals, stamens, and carpels.

Sepals are the outermost part of the flower and usually green in color. They protect the developing flower bud and are often the same color as the leaves of the plant. Petals are the brightly colored parts of the flower that often attract pollinators. They are typically soft and delicate and give the flower its distinctive shape.

Stamens are the male reproductive structures of the flower and are composed of two parts: the filament and the anther. The filament is a long, thin stalk that supports the anther. The anther is where pollen is produced and contains the male gametes (sperm).

Carpels are the female reproductive structures of the flower and are composed of three parts: the stigma, the style, and the ovary. The stigma is the sticky tip of the carpel that traps pollen. The style is the long, slender stalk that connects the stigma to the ovary. The ovary contains the female gametes (eggs) and develops into a fruit after fertilization.

Together, these four structures make up a typical flower. However, not all flowers have all four structures, and some have additional structures such as nectaries (structures that produce nectar to attract pollinators) or bracts (modified leaves that protect the flower).

In summary, the structure of a flower is essential to its function in plant reproduction. Sepals, petals, stamens, and carpels work together to produce and transfer gametes, attract pollinators, and protect the developing flower bud. Understanding flower structure is crucial for gardeners, plant enthusiasts, and anyone interested in the fascinating world of plants.

Diagram of a complete flower showing the four main floral parts and their components (left)

Flower Structure: Non-Reproductive Parts

In a flower, the reproductive components include the female structure called the gynoecium, which is the innermost whorl of the flower. The gynoecium is formed by carpels, which are commonly called pistils. A pistil can be formed by one (single pistil) or more fused carpels (compound pistil).

Each carpel has three parts: the ovary, the style, and the stigma. The ovary is the sac-like structure that contains the ovules, which contain an egg cell inside. The style is an elongated stalk that connects the ovary and the stigma. The stigma is the tip of the style that is sticky and captures pollen.

Sepals and petals, on the other hand, are non-reproductive components that either protect the reproductive components or attract pollinators. Sepals are typically leaf-like and smaller than petals, and they form the calyx, which is the outermost whorl on the receptacle. You can see sepals covering and protecting an unopened flower bud.

Petals are typically the colorful and conspicuous structures of the flower that attract pollinators. They form the corolla, which lies within the calyx. Together, sepals and petals form the perianth.

Understanding the female structure of a flowering plant is crucial for plant enthusiasts, gardeners, and anyone interested in the fascinating world of plants. The carpels or pistils are the female reproductive structures, and they play a key role in plant reproduction. The ovary, style, and stigma work together to receive and transfer pollen, which is essential for fertilization and the production of seeds.

Flower Structure: Male Structure of a Flowering Plant

In a flower, the androecium corresponds to the male structures of the plant and is the whorl that lies between the gynoecium and the corolla. The androecium is composed of stamens, which produce the pollen that contains the sperm. A flower usually has several stamens, and each is composed of a filament and an anther. The filament is a long and thin stalk that holds the anther, which is a sac-like structure that produces the pollen.

All four flower parts, including the androecium, are modified leaves as part of the shoot system. Each part forms a whorl in the floral receptacle, creating four concentric circles. However, any of the four floral parts can be highly modified and have a different function than the typical one. For example, stamens can be sterile and colorful, taking the role of petals. In some plants, the petals are missing, and the colorful, attracting structures for pollinators are the sepals.

Flowers can exist in many combinations, and some are incomplete flowers that lack one of the components. A flower with all four components is called a complete flower. Flowers can also be classified as perfect, which means they are bisexual and present both androecium and gynoecium, or imperfect, which means they are unisexual (a female flower is called carpellate, and male flowers are staminate). A plant can have bisexual, unisexual, or both types of flowers.

A plant is monoicous when it bears both unisexual flowers, and dioicous when an individual plant bears only female or only male flowers. Understanding flower classification is essential for gardeners, plant enthusiasts, and anyone interested in the fascinating world of plants. By knowing the different types of flowers, you can better understand how plants reproduce and how to care for them.

Flower Structure and Reproduction

For a plant to reproduce sexually, the male gamete has to reach and fertilize the female gamete. Unlike animals, plants do not move, but they have evolved diverse mechanisms to accomplish pollination.

In most flowering plants, the flower is central to this task. Plants make use of pollinating agents to move the pollen among flowers. While some plants use wind or water for pollination, the great majority rely on animals (insects, birds, and mammals) to transport the pollen.

Pollination is the transfer of pollen from the male reproductive structure to the female reproductive structure in seed plants. Angiosperms use flowers to attract pollinators. Most of a flower’s traits (size, color, nectar, scent) are for attracting a type of pollinator (or not attracting it, if it uses wind for pollination), sometimes even a specific animal species.

Colorful flowers typically attract birds and some insects. But some plants have inconspicuous flowers. For example, grasses belong to the family Poaceae, a big, diverse group that includes grass, pastures, cereal grasses, and bamboo. Most grasses are pollinated by wind or insects and thus typically have very small, colorless, or beige-ish flowers.

Pollinators are attracted to flowers by visual cues such as color and shape, as well as by scent and nectar. When an animal visits a flower, pollen from the anther sticks to the animal's body, and as it moves to another flower, some of the pollen rubs off onto the stigma, allowing for fertilization to occur.

Understanding pollination is essential for gardeners, plant enthusiasts, and anyone interested in the fascinating world of plants. By knowing how plants reproduce and how pollination occurs, you can better understand how to care for plants and even help to promote pollinator populations in your area.

What happens after pollination?

Pollination is just the first step in the process of plant fertilization. Once pollen grains are transferred from a flower anther to the stigma of another flower, the process of fertilization can begin.

Once on the stigma, the pollen grain germinates, developing a pollen tube. The pollen tube is a long and slender tube that goes all the way down through the style and reaches the interior of the ovary. The sperm, which is inside the pollen grain, moves through this tube to the ovary.

Once inside the ovary, the sperm reaches the female gamete and fertilization occurs. The fertilized egg develops into a seed, and the ovary becomes a fruit. The fruit is the mature ovary that contains the seeds.

The process of fertilization in plants is a complex and fascinating one, involving multiple steps and specialized structures. Understanding the process of fertilization is essential for gardeners, plant enthusiasts, and anyone interested in the fascinating world of plants.

By knowing how plants reproduce and how fertilization occurs, you can better understand how to care for plants and even help to promote pollinator populations in your area.

Pollen germination (1) and fertilization (2)
Pollen germination (1) and fertilization (2)

In summary, the flower is the sexual reproductive part of angiosperms that bears the gametes and commonly attracts pollinators. The non-reproductive sepals and petals mainly protect the reproductive parts and attract pollinators.

The reproductive stamens and carpels/pistils bear the sperm and eggs in a flower. In angiosperms, sexual reproduction occurs in the flower when the pollen (which contains the sperm) reaches and fertilizes the egg inside the ovary.

Flowering plants rely on pollinating agents (wind, water, or animals) to transport the pollen among flowers. Most of a flower’s traits (size, color, nectar, scent) are related to the specific pollinating agent that the plant uses.

The ovary contains one or more ovules, each with an embryo sac containing one egg cell. Fertilization in angiosperms is called double fertilization, where one sperm fertilizes the egg cell, forming a zygote that develops into the plant embryo.

The ovary grows to become the fruit, which helps in seed dispersal. Fruits can be colorful and nutritious to attract animals that eat them and disperse the seeds or have modifications to allow them to stick to an animal's fur or feathers. Likewise, seeds dispersed by wind are small, weightless, and modified to be able to “fly” with the wind.

Understanding the structure and reproductive process of flowers is essential for gardeners, plant enthusiasts, and anyone interested in the fascinating world of plants. By knowing how plants reproduce and how pollination and fertilization occur, you can better understand how to care for plants and even help to promote pollinator populations in your area.


Lisa Urry et al., Biology, 12th edition, 2021.

Flower Structure

Which structure of a flower traps pollen?

The structure of a flower called stigma is sticky and traps the pollen. The stigma is the tip of the female reproductive structure, the pistil or carpel.

Which structure is a stalk that supports a single flower?

The stalk that supports a single flower is the peduncle, however, it can also bear a group of flowers. In this case, each flower is supported by a pedicel.

What is the structure and function of a flower?

A flower structure includes four floral parts: the non-reproductive sepals and petals and the reproductive stamens and carpels/pistils. A flower bears the gametes, and its function is to facilitate the sexual reproduction of the plant by attracting pollinators.

What are the male structures of a flower?

The male structures of a flower are the stamens that produce the pollen. Stamens are collectively called the androecium. 

What structure of the flower receives pollen?

The structure of the flower called the stigma receives pollen which then moves through the style to finally get to the ovary where it fertilizes the ovules.

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