This lesson will investigate the structure of the flower known as the corolla. The lesson will also explore the variation in this structure as well as its function and importance in plant reproduction.
What Is a Corolla?
When you look at a flowering plant, what’s the first thing you notice? Is it the stem, the leaves, or the flower? On most flowering plants, the most noticeable feature is the brightly-colored petals of the flower. The petals of flowers are often arranged in a circle around the center of the flower, and this collective unit of petals is referred to as the corolla.In addition to the corolla, most flowers have three other circles of structures that make up a complete flower. On the outside of the corolla, most flowers have sepals, or small leaf-like structures that enclose the petals before the flower opens. The first circle of structures on the inside of the corolla is made up of the male reproductive organs of the flower, including the many stamen.
The circle at the center of the flower consists of the female reproductive organs, which are collectively referred to as the pistil.
Variation in Structure of the Corolla
As you have probably noticed when observing a garden, there is a wide variety in the colors and designs of flowers.
The corolla of different species of plants can vary in color, size, and the number of petals. Many large flowers have fewer petals within the corolla, while smaller flowers may have greater numbers of petals.Flowers can be divided into two different types based on the symmetry of their corolla. Flowers that have identical petals arranged in a circle around the center of the flower are said to have radial symmetry and are called actinomorphic flowers. Radial symmetry is when a mirror image can be produced when a line is drawn in any direction across the center of the flower. Flowering plants that are actinomorphic include sunflowers, lilies, and buttercups.The second type of symmetry used to describe the corolla of flowers is called bilateral symmetry.
This is when only one line can be drawn to create a mirror image through the middle of the flower. Flowers that have bilateral symmetry are called zygomorphic flowers, and they often have petals of different shapes and sizes within the corolla of the flower. The most common example of flowers that are zygomorphic are orchids.
Function of the Corolla
Overall, the main function of the corolla is to assist in the reproductive process of the plant. The petals of the corolla are designed to aid in pollination, and therefore, increase the chance of successful reproduction of the flower.
Some plants are pollinated when wind picks up their pollen and transfers it to another flower of the same species. For plants that use wind pollination, the corolla assists this process by having small petals. The small petals do not block the wind, and make it possible for wind to move over the anther (which makes the pollen grains), and transfer it to another flower.The color and texture of the petals of the corolla also play an important role in pollination.
Many plants that rely on animal pollinators have specific animal species that pollinate them. In order to attract certain animal species, the flowers have developed petals with colors specifically pleasing to those animals.Flowers that have red petals attract birds, while yellow and blue petals attract insects because they cannot see the color red.
You may notice that some flowers are pale colored, and wonder what types of animals are attracted to these flowers. These flowers are designed to attract night pollinators, such as moths and bats, and their pale colors stand out against the dark night sky.Some flowers also have intricate color patterns that not only attract the pollinator but also help guide them towards the middle of the flower, where the pollen is located. These color patterns serve a similar function to the lights on the runway of an airport; they both help guide the flying object toward the desired location.
The petals of the corolla can also have a variety of textures, which aid in successful pollination. Similar to the color patterns near the center of the flower, some petals also have textured sections that help guide the pollinator toward the pollen. In addition to guidance, textured sections of the petals also serve to help the pollinator attach to the flower. If the flower petals were too smooth, the pollinators might slip off of the flower, and this would decrease reproductive success due to time being wasted having to climb back up to the flower.
Next time you see some flowers blooming, take a closer look and see if you can identify the individual petals that make up the corolla. Also, look at all of the different colors, shapes, and sizes of petals that you can find. Although there is wide variation in structure and design, all corollas serve the same function, which is to aid the plant in the reproductive process.
- corolla: collective unit of petals often arranged in a circle around the center of the flower
- sepals: small leaf-like structures that enclose the petals before the flower opens
- stamen: the male reproductive organs of the flower
- pistil: the female reproductive organs of the flower
- actinomorphic: flowers that have identical petals arranged in a circle around the center of the flower are said to have radial symmetry
- radial symmetry: a mirror image can be produced when a line is drawn in any direction across the center of the flower
- bilateral symmetry: when only one line can be drawn to create a mirror image through the middle of the flower
- zygomorphic: flowers that have bilateral symmetry; they often have petals of different shapes and sizes within the corolla of the flower
Expanding your knowledge of the corolla through this lesson could lead to your ability to:
- Recognize the corolla of a flower
- Outline the different structures of the corolla
- Explain the function of the corolla in nature