The Role of Sepals in Flower Development and Protection

Sepals are small leaf-like green outermost part of flowers. Together, they form the outermost whorl of a flower. This whorl is called the calyx. Sepals function as protective structures that cover the bud and provide structural integrity to the petals that form the corolla. There are different types of sepals based on their shapes and modifications. Some commonly observed examples of sepals include the urn-shaped green structure at the base of Hibiscus, marigolds, etc., and a cap-like green structure at the top of brinjal, tomato, etc.

What is Sepal?

Sepals are small, leaf-like, green-coloured parts of the flower which perform the function of protecting the rising buds. They form the vegetative part of the flower and support the petals when it bloom. In some plants, they remain persistent even in fruits. Common examples of such types are seen in brinjal, tomato, etc. In some plants, the Sepals act as a defense organ by getting modified into spines. Sepals together form the calyx which is the outermost whorl of a flower. They can be unified or separate. However, in some plants such as tube roses, the sepals may be fused with petals and form the tepals. Based on their shape and size the sepals can be distinguished into different types.

Structure of Sepals

Sepals are the green-coloured vegetative structures, which are a characteristic feature of flowering plants better known as the angiosperms. Sepals are located at the base of the flower, forming the outermost whorl, often encircling and protecting the developing bud and are collectively termed as the calyx. Unlike petals, which are usually soft and colorful, sepals are often tougher and less conspicuous. In a complete flower, i.e. one which has all the four floral parts (sepals, petals, stamen and carpel), the sepals are attached to the floral stalk by a receptacle.

The sepals mainly comprise the:

• parenchyma
• secretory cells known as laticifers
• tannin cells and
• other specialized plant cell organelles

Though sepals are mainly green, they can also be of varied colors depending on the plant species. Green coloured sepals contain plastids that contain chlorophyll, better known as chloroplasts along with the differentiated palisade and spongy mesophylls. Both monocots and dicots have sepals, but the difference lies in the number of sepals present in the flowers of monocots and dicots. The monocots have floral parts in the multiples of three whereas dicots tend to have floral parts in the multiples of four or five. Hence, the monocots are termed trimerous and the dicots on the other hand are termed as tetramerous or pentamerous.

Types of Sepals

While sepals generally serve a protective function, they can exhibit different forms and adaptations in various plant species. The different types of sepals are:

• Regular Sepals: Many flowers have regular-shaped sepals that are green and protective in nature. They form the outermost layer of the flower bud, providing support and shielding inner floral parts. Example lily.
• Modified Sepals: Flowers like orchids often have modified sepals that resemble petals. These sepals may be highly decorative and play a role in attracting pollinators. These sepals can vary widely in shape and color.
• Fused Sepals: In some plants, the sepals are fused into a single structure, forming a tubular calyx. This adaptation is characteristic of many members of the mint family.
• Bract-like Sepal: In some plants like Poinsettias have colorful bract-like structures that are often mistaken for petals. In actual their flowers are small and inconspicuous and have small green sepals that may resemble bracts.
• Reduced Sepals: In some plants like poppies, the sepals are often reduced in size and may be overshadowed by the large, colorful petals. These are reduced sepals.

Functions of Sepals

The functions of Sepals are stated below:

• Sepals are present at the base of the flower and act as a natural shield by encasing the petals and other floral parts, hence providing protection against environmental threats such as extreme weather conditions, grazing animals and pests.
• Sepals also prevent the flower from drying out and play a role in the adaptation of plants to their environment.
• In some plants that lack petals, sepals function as petals and help in attracting pollinators. Example, Bougainvillea and Clematis.
• Sepals protect both flowers and fruits by secreting chemicals that are capable of warding off predators.
• In some plant species, sepals serve as thorns and function by protecting the flowers. For example, in water chestnuts the thorns are a modification of sepals.
• While sepals generally serve a protective function, their appearance can vary significantly among different plant species. Some flowers have sepals that closely resemble the petals, creating a harmonious and unified appearance. In contrast, other flowers have sepals that stand out distinctly from the petals, offering a complementary or contrasting visual effect. The diversity in sepal morphology adds to the fascinating array of floral structures found in nature.
• The buds are under the protective cover of sepals until they’re ready to bloom. The sepals then shed off in most cases.
• In some cases, sepal grows larger and protects the fruits from honey bee, birds and different kinds of insects and pests.
• The calyx is commonly persistent and remains patent when the fruit ripens, in contrast to the other floral parts that shed off once the fruit matures. Example, persimmon (Diospyros virginiana)

Conclusion – Sepals

Sepals therefore, are one of the most important parts of a flowering plant that perform the unique and pivotal function of providing protection to the rising bud from environmental factors. It may also sometimes perform various other functions like attracting pollinators or providing protection against grazing animals when modified to form thorns but the primary function remains to be of protecting the buds and fruits.

FAQs – Sepals

What do You Mean by Tepals?

In some sepals and petals are not distinguished. In this plant the calyx and the corolla fuse to form the perianth. Each member of the perianth are called tepals. Example, as seen in tube rose.

What are Sepals?

Sepals are green coloured leaf life structures present at the base of the flower that perform the primary function of protecting the buds against environmental factors during its development.

What is the Structure of a Sepal?

Sepals are small in size, green in color and leaf life in appearance that forms the outermost part of a flower. In some plants they can be modified to serve as the the part for attracting pollinators, in some plants it can get modified as spine, spurs etc.

What is an Example of Sepal?

A common example of sepals can be seen in Hibiscus. If we look at the base of the flower we will find an urn shaped green structure that holds the other floral whorls within it. That is the calyx formed of fused sepals. The persistent calyx of the brinjal also represents the sepals.

Why are Sepals green in Color?

Sepals are mainly green in color. They contained a color pigment i.e., chlorophyll, which is responsible for the green color of sepals.