A complete flower's anatomy is required to have sepals, petals, pistils, and stamens. Below, each of these anatomical structures is explained in more detail.
Sepals
Sepals are often confused with petals or leaves. Sepals are protective structures that are found on the outside of the petals. Sepals can be green and appear like small leaves or underdeveloped petals. In some flowers, the sepals are highly colorful and appear to be part of the petals. Sepals are generally protective structures that prevent damage to the flowers as they develop and may continue to protect mature flowers. In some species, sepals produce chemicals that assist in preventing pests from damaging the flower.
Some flowers do not have petals but still need to attract pollinators. In these instances, sepals may function as petals and may be brightly colored. Clematis are large, colorful flowers that are common among gardeners. While attractive, the large, colorful components of the clematis are sepals, not petals.
Petals
Petals are typically the attractive and colorful part of the flower. For most flowers, petals function to attract pollinators. Vivid colors and shapes are attractive to many insects that are important plant pollinators. Petals are also the production sites of essential oils that give flowers their floral scent. Flowers are often shaped throughout many years of evolution to attract a specific pollinator. Because of this, the scent and pattern of petals can vary dramatically from plant to plant. For instance, while rose petals give off a pleasant perfume-like scent, Bradford pears are notoriously putrid smelling.
Pistils
The pistil is a female structure on a flower. A pistil is composed of four parts: a stigma, style, ovary, and ovule. Stigmas are the tip of the pistil which are supported by the style. The ovary is the structure forming the base of the pistil, which contains the ovule. In many fruits, the ovary becomes the edible portion. For instance, the fleshy, edible portion of an apple is the ovary, while the apple seeds are mature ovules. Pistils are found in the middle of the flower.
Stamen
The stamen is the male reproductive component of a flower. It has two parts: the anther and the filament. The anther is the tip of the stamen that is covered in pollen. In wind-pollinated plants, gusts of wind blow this pollen into the air in hopes that it will land on a pistil's stigma. In flowers that require pollinators, the pollen sticks to the outer surface of an organism and is deposited on the stigma of another flower that the organism visits. There are many different methods that animals use to disperse pollen. Below the anther, the filament acts as a stalk to support the pollinating head and connect it to the flower.
Complete Flower Diagram
The following complete flower diagram highlights the required portion of a complete flower. In this example, a general flower plan is illustrated where the petals are the main structure, and the sepals are reduced. Recall that in many flowers, the petals and sepals may appear differently depending on the plant's evolutionary needs.
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Many flowers are complete flowers. The following list of flowers are examples of those that contain all 4 required components of complete flowers:
- Hibiscus
- Tulips
- Roses
- Sweet peas
- Lemon
- Tomato
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Angiosperms are plants that produce flowers, which are reproductive structures that result in seed production. Flowers are complete flowers if they possess sepals, petals, pistils, and stamens. Sepals are protective outer coverings that may sometimes appear like leaves or petals. Petals are typically attractive, aromatic structures used to attract pollinators. Pistils are female reproductive structures composed of a stigma, style, ovary, and ovule. Stamens are male reproductive structures that are composed of an anther and filament. Examples of complete flowers include hibiscus, tulips, and pea plants.
Complete flowers are always perfect flowers, which contain male and female parts. However, not all perfect flowers are complete, as perfect flowers may have both pistils and stamen but lack sepals and petals. Imperfect flowers contain only one of two sex structures. This means that even if they possess both petals and sepals, because they are lacking either a stamen or pistil they are always incomplete flowers, which is any flower that is missing one or more of the four required components of a complete flower. Examples of incomplete flowers include pumpkin flowers and many trees.
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Video Transcript
What Makes a Flower Complete?
'A rose by any other name would smell as sweet.' Although Shakespeare probably didn't have biology in mind when he wrote this line, we can also call a rose a complete flower in the world of biology. According to their structures, some flowers - like roses - are considered to be complete, while others are classified as incomplete.
In order for a flower to be considered complete it must have four parts: sepals, petals, stamens and pistils. Incomplete flowers lack one or more of these parts. Before we get into more detailed definitions, let's examine where you can find each part on a complete flower.
If you look at a cross section of a rosebud, you'll notice the green sepals on the outside. The sepals surround the rose's red petals, and if you carefully pull back the petals, you'll find the yellow stamens. The stamens surround the rose's pistils in the center. Moving from the outermost layer to the center, we go from sepals to petals to stamens to pistils. This order is true for any complete flower. Now, let's see what each part does for the flower.
Structure of a Complete Flower
Flowers function as reproductive structures for many plants, and each part of a complete flower helps the flower serve that ultimate purpose.
At the outermost layer, we have sepals, which are the leaf-like, usually green structures at the flower base. They function to protect the flower as it's forming. You can think of it as the armor that helps flowers survive long enough to reach reproductive maturity.
Petals are the colorful parts of the flower that function to attract pollinators. Different petal colors can attract different types of animals and insects to act as pollinators. For example, many butterfly species are drawn to flowers with red or yellow petals. Sepals and petals are often referred to as the sterile parts of the flower because they don't carry out sexual reproduction. For that step, we need stamens and pistils.
A complete flower may have one or more stamens. Stamens are male reproductive parts of a flower. Each stamen looks like a long tube with a ball on the end. The tube is called the filament, and the ball on top is called the anther. The anther produces pollen grains, which contain the flower's sperm. When pollinators come into contact with the anther, they may carry pollen grains away to fertilize a flower.
Just like with stamens, a complete flower may have one or more pistils. Pistils are the female reproductive parts of the flower. A pistil is often bottle-shaped, and it has three main parts: the stigma, style and ovary. The sticky surface on top of the pistil is called the stigma. When a pollinator rubs a flower the right way, pollen will stick to the stigma.
The style is a slender stalk that connects the stigma to the ovary. You can think of it as the neck of the bottle. Pollen grains deposited on the stigma form pollen tubes that burrow through the style to reach the ovary. The ovary is a hollow cavity that contains immature seeds called ovules - you can think of it as the body of the bottle. Once a pollen tube reaches the ovary, it deposits sperm cells, which will fertilize an egg waiting inside an ovule. The fertilized ovule develops into a seed that may one day create another plant with more complete flowers.
Also, you may hear the term carpel used instead of pistil to describe the female flower parts. While the terms can sometimes be used interchangeably (when a single carpel makes up a single pistil), that's not always the case (when multiple carpels fuse together to form a compound pistil). Now that you have a better understanding of how the parts of a complete flower work together, let's look at a few more examples.
Examples of Complete Flowers
Complete flowers are very common - they are very successful at reproducing since they have both male and female reproductive parts in one flower. Most likely, you are not far from a complete flower at this very moment. Other than roses, some common examples of complete flowers include hibiscus, pea plants and tulips.
Hibiscus plants grow all over the world, and they are very beautiful and come in a variety of colors. If you look closely at a hibiscus flower, you will be able to see the green sepals at the tops of the stem. Above the sepals will be the beautifully colored and fragrant petals. Sticking out from the center of the flower will be a long pistil. Growing from the sides of the pistil you will be able to see numerous stamens.
The first plant extensively studied in genetics was the pea plant. One of the reasons that the famous geneticist Gregor Mendel studied the plant was that it is a complete flower. If you look closely inside the flowers of a pea plant in your garden, you will see all of the four required parts.
Tulips are famous all over the world. These popular flowers are also prime examples of complete flowers. The next time you walk by a tulip, if you look inside the petals, you will see a central pistil with stamens all around. If you look below the petals, you will also see the sepals.
Lesson Summary
As you can see, complete flowers are very common. In order for a flower to be considered complete, it must have sepals, petals, at least one stamen and at least one pistil. Flowers serve as reproductive structures for many plants, and the parts of a complete flower help ensure its reproductive success. Complete flowers have both male and female parts, which offer reproductive benefits. Common examples of complete flowers include hibiscus, roses, pea plants and tulips.
Complete Flower Vocabulary & Definitions
| Vocabulary | Definitions |
|---|---|
| Sepals | leaf-like green structures at the flower base |
| Petals | the colorful parts of the flower that function to attract pollinator |
| Stamen | male reproductive part of a flower, looks like a long tube with a ball on the end |
| Filament | the long tube |
| Anther | the ball produces pollen grains, which contain the flower's sperm |
| Pistil | the female reproductive part of the flower |
| Stigma | sticky surface on top of the pistil |
| Style | a slender stalk that connects the stigma to the ovary |
| Ovary | a hollow cavity that contains immature seeds called ovules |
Learning Outcomes
When this lesson is done, students should be able to:
- Describe a complete flower
- Identify the parts of a flower
- Cite examples of common flowers
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