Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Flower Structure

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Biology

Do you like flowers? Flowers are diverse in shape, size, color, and scent! But not all plants have flowers. Have you ever seen a pine or a cypress with flowers? Flowers are only found in angiosperms, a group of plants commonly known as flowering plants. Fowers are involved in plant reproduction, produce the eggs and sperm of the plant, are the site of sexual reproduction, and attract pollinators that transfer the sperm among the flowers. We describe the flower structure, 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 in plants commonly known as flowering plants. Flowering plants compose the clade Angiospermae (from the Greek “angeion” = vessel, and “sperma” = sperm or seed) and have, besides flowers, ovules enclosed by an ovary (that become seeds enclosed in a fruit).

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

Flower: the reproductive structure of angiosperms, composed of modified leaves, which bear the reproductive cells (gametes) and are the site where sexual reproduction occurs.

Angiosperm: a plant that produces flowers and fruits, and its ovules are enclosed in an ovary.

Sexual reproduction involves the fusion of two haploid gametes to produce a diploid zygote.

Flowers present a great variety of sizes, shapes, and colors. They can develop as single flowers or in groups called inflorescences (Figure 1). Flowers are part of the plant shoot system (including non-reproductive leaves, stems, and reproductive flowers) and develop from a stalk called a peduncle. In inflorescences, each flower has a pedicel that attaches them to the main axis. The tip of a peduncle or a pedicel is the receptacle, which contains the flower parts.

Tulips, roses, and magnolias are relatively big individual flowers. Snapdragons and lilac are inflorescences. What about sunflowers? They look like big individual flowers; however, sunflowers are 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. Besides, the tiny flowers develop on a big receptacle and do not have individual pedicels.

Flower Structure Flower diversity examples StudySmarter

Figure 1. Flower diversity. From left to right: a rose develops as an individual flower; the next three images show different types of inflorescences: lilac, sunflower, and grass. Source: all images CC0, via Wikimedia Commons.

Flower Structure in a Diagram Labeled

No matter a flower’s size, shape, or color, its function is the sexual reproduction of the plant, and thus it has structures that carry the plant gametes (eggs and sperm, which are the sexual reproductive cells). A typical flower is composed of four floral structures: sepals, petals, stamens, and carpels (Figure 2).

Flower Structure Diagram of flower parts StudySmarter

Figure 2. Diagram of a complete flower showing the four main floral parts and their components (left). The floral parts are arranged in whorls (right): 1-calyx, 2-corolla, 3-androecium, and 4-gynoecium. Source: left, LadyofHats, Public domain; right, modified from Nefronus, CC0; both images via Wikimedia Commons.

Flower Structure: Non-Reproductive Parts

Sepals and petals form the perianth and are non-reproductive components that either protect the reproductive components or attract pollinators.

The sepals are typically leaf-like and smaller than the petals. The group of sepals forms the calyx. These are the ones you see covering and protecting an unopened flower bud. The calyx is the outermost whorl on the receptacle. Petals are typically the conspicuous and colored structures of the flower that attract pollinators. The group of petals forms the corolla. The corolla whorl lies within the calyx.

Flower Structure: Female Structure of a Flowering Plant

The reproductive components of a flower include the carpels that form the female structure called the gynoecium (the innermost whorl of the flower). The carpels are commonly called pistils. A pistil can be formed by one (single pistil) or more fused carpels (compound pistil, for example, the right diagram in Figure 2 shows three fused carpels). A carpel has three parts: the ovary in the base is the sac-like structure that contains the ovules (with an egg cell inside), the style is an elongated stalk that connects the ovary and the stigma, and the stigma, which is the tip of the style that is sticky, for capturing pollen.

Flower Structure: Male Structure of a Flowering Plant

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

As part of the shoot system, all four flower parts are modified leaves. Each part forms a whorl in the floral receptacle, thus creating four concentric circles. 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.

A flower with these four components is called a complete flower. However, flowers exist in many combinations, and some are incomplete flowers that lack one of the components. They can also be classified as perfect - when they are bisexual, presenting both androecium and gynoecium - or imperfect - when they are unisexual (an only female flower is called carpellate, 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.

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.

How does the sperm get to the egg in flowering plants?

Plants have evolved diverse mechanisms to accomplish this, and 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. Have you seen grass flowers? They pass unnoticed by most people. Grass belongs to the family Poaceae, a big, diverse group that includes grass, pastures, cereal grasses, and bamboo. The wind or insects pollinate most grasses and thus, have typically very small, colorless, or beige-ish flowers (see figure 1, the last image at the right is from a grass). You will learn more about Pollination here.

What happens after pollination?

Irrespective of the pollinating agent, pollen grains are transferred from a flower anther to the stigma of another flower. 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 (Figure 3).

Flower Structure Fertilization diagram StudySmarter

Figure 3. Pollen germination (1) and fertilization (2). Source: modified from LadyofHats, Public domain, via Wikimedia Commons.

The ovary contains one or more ovules. Each ovule contains an embryo sac with a few cells including one egg cell. One sperm fertilizes the egg cell forming a zygote. The zygote develops into the plant embryo, contained in the ovule that develops into the seed.

Fertilization in angiosperms is called double fertilization.

The seed or seeds are enclosed by the ovary that grows to become the fruit. The fruit helps in seed dispersal, and its characteristics (colorful and nutritious or inconspicuous and weightless) depend on the dispersal method. When the seed germinates, a new plant develops, and the cycle starts again.

Fruits can be colorful and nutritious (and delicious!) like apples, mangoes, guavas, and figs, to attract animals that eat them and disperse the seeds. On the other hand, some fruits are also dispersed by animals not by eating them but by transporting them in their fur or feathers. In this case, fruits have to be small and have shape modifications or structures that allow them to stick to an animal's fur or feathers when they walk by (like burs that have spikes or hooks). Likewise, seeds dispersed by wind are small, weightless, and modified to be able to “fly” with the wind (like a dandelion seed with its feathery fruit).

Flower Structure - Key Takeaways

  • The flower is the sexual reproductive part of angiosperms that bears the gametes and commonly attracts pollinators.
  • In a flower, 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.

References

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

Flower Structure

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.

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.

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.

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

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. 

Final Flower Structure Quiz

Question

The transference of pollen grains from the male reproductive structure to the female one is called:

Show answer

Answer

pollination

Show question

Question

After fertilization, the ____ develops into the seed, and the ____ becomes the fruit. 

Show answer

Answer

ovule, ovary

Show question

Question

Which of the following features are only found in angiosperms?

Show answer

Answer

Flowers

Show question

Question

A peduncle can bear___, while a pedicel only bears____.

Show answer

Answer

a single flower or an inflorescence, a single flower from an inflorescence

Show question

Question

Which of the following are reproductive parts of a flower?


Show answer

Answer

perianth

Show question

Question

Which of the following are non-reproductive parts of a flower?


Show answer

Answer

perianth

Show question

Question

What are the four parts of a flower that are arranged in concentric whorls? Mention them from the innermost to the outermost whorl.

Show answer

Answer

Pistils (gynoecium), stamens (androecium), petals (corolla), and sepals (calyx).

Show question

Question

Which of the following are the female reproductive parts of a flower?


Show answer

Answer

perianth

Show question

Question

Which of the following are the male reproductive parts of a flower?


Show answer

Answer

perianth

Show question

Question

Which of the following parts function in protecting and/or attracting pollinators?


Show answer

Answer

perianth

Show question

Question

Where are pollen grains produced in a flower?


Show answer

Answer

stamens

Show question

Question

In ___ plants a bee that is collecting pollen could pollinate another flower in the same plant, while in a ___ plant it would have to move to another plant to pollinate a flower.

Show answer

Answer

monoicous, dioicous

Show question

Question

Why are flowers so diverse in traits like size, shape, color, nectar, or scent?

Show answer

Answer

Flowers are so diverse because most of their traits are related to the pollinating agent, and in the case of animal pollination they serve for attracting a specific animal group or even species.

Show question

Question

Which of the following represents the best order in which a pollen grain moves and reproduction occur for a flowering plant?

Show answer

Answer

Anther, stigma, style, ovary, ovule, fertilization, seed, fruit

Show question

Question

Which of the following is true about the fruit?

Show answer

Answer

It encloses the embryo

Show question

60%

of the users don't pass the Flower Structure quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.