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Sepals are the green-coloured outermost component of flowering plants that provide support to the petals during the blooming stage. These are small, leaf-shaped parts of angiosperm that provide protection to the rising buds.
- The cells of green sepals contain chloroplasts, distinct palisade, and spongy mesophylls.
- Noël Martin Joseph de Necker proposed the term sepalum in 1790.
- Depending on the type of flowering plants, sepals vary in terms of shape and size.
- It is derived from the Greek word sképē, meaning covering.
- Together, all the sepals in a flower are referred to as the calyx, which forms the outermost whorl of a flower.
- They are able to perform photosynthesis because they contain chlorophyll.
- Some common examples of sepals include Hibiscus and marigolds.
| Table of Content |
Key Terms: Sepals, Calyx, Functions of Sepals, Flowering Plants, Whorls, Angiosperm, Photosynthesis, Chlorophyll, Structure of Sepals, Function of Sepals
What are Sepals?
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Sepals are modified leaves that form the vegetative part of flowering plants. After being modified into spines, they act as defense organs.
- Sepals provide protection against grazing animals or attract pollinators when modified into thorns.
- They are found in various numbers in either fused or separated states.
- The arrangement of sepals and petals in flower buds before blooming is called aestivation in plants.
- Since they are non-reproductive parts of the flower, they are neither male nor female.
- The combination of sepal and petal as a whole is called perianth.
- They are usually found in two conditions such as:- Gamosepalous Condition and Polysepalous Condition
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Structure of Sepals
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Sepals are the outermost layer of a flower, which is found at the base of the flower. They are tougher and less conspicuous vegetative parts that form one of the four parts of flowering plants.
- Sepals serve as a natural defence that protects the flower's petals and other floral parts from harsh conditions, grazing animals, and atmospheric pollutants.
- They consist of tannin cells, parenchyma, secretory cells, and other specialized plant cell organelles.
- Sepals are attached to the base of the floral stalk by the receptacle.
- Their colour varies according to the species of the flowering plants.
- Some sepals are fused together to form a cup-like shape around the petals of the flower.
- The identifiable characteristic of this part of the flower is shared by both monocots and dicots plants.
- The total number of sepals in each type of plant's flower varies; usually, a flower has 2–5 sepals.
Sepals
Calyx
The calyx of flowering plants refers to the group of all the sepals in a flower. It is located at the base of the flower at the top of a stem.
- The name calyx is derived from the Greek word “kalyx,” meaning “husk” or “pod.”
- It supports the internal structures of flowers, such as the androecium, corolla, and gynoecium.
- The hibiscus shows the epicalyx or the second layer of sepals.
- It is one of the structural components of the flower and provides protection in windy conditions.
- Calyx helps in regulating the uptake and retention of water within the flower bud.
Types of Sepals
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Different types of sepals exist in nature. The three main types are as follows:
Fused Sepals
When sepals in certain plants are fused into a single structure, they will form a tubular calyx. A classical example of fused sepals is Hibiscus (China Rose). The condition in which sepals are fused is called gamosepalous condition.
Bract-like Sepals
Certain plants have vibrant structures that resemble bracts-like sepals and are frequently misunderstood as petals. Their flowers are small and unnoticeable, with tiny green sepals that sometimes have a bract-like appearance.
Modified Sepals
Modified sepals are sometimes imitated with petals, which are seen in flowers like orchids. The structure and colour of these sepals can differ greatly. These types of sepals are used for decoration and play an important role in attracting pollinators.
Regular Sepals
Flowers that are green and protective in nature form regular-shaped sepals. They form the outermost layer of the bud of the flower, thus shielding the inner floral parts. Lily is the most common example of a regular sepal.
Functions of Sepals
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Sepals play an important role in angiospermic plants. Some of their functions are mentioned below:
- Sepals provide protection to flowers so that they don't get dried out.
- They help flowers adapt to different environmental conditions
- It also produces harmful chemicals to keep fruits and flowers safe from predators.
- Since they are green in colour, sepals can produce food as well.
- When the flower is closed before and after pollination, it acts as a shield for the other floral components.
- In some cases, sepal protects the fruits from birds, bees, and insects and pests.
- It provides protection to the reproductive organs within the flower.
- In plants with no petals, sepals will act like petals.
Things to Remember
- Sepals are leaves that provide a protective structure to flower at the budding stage.
- The buds are covered until they are ready to bloom and form a flower.
- Chlorophyll is the green pigment that gives sepals their green colour.
- They can be free or connate depending on whether a tube with valvate or bilabiate lobes is visible.
- Sepals are sometimes overshadowed by the large, colorful petals.
Read More:
| Chapter Related Concepts | ||
|---|---|---|
| Contraception | Maternal mortality rate | Infant Mortality Rate |
| Gemmule formation | Double fertilization | Oestrus Cycle |
Sample Questions
Ques. What is a complete flower? (3 marks)
Ans. A complete flower is defined as one that possesses all four whorls, namely the petals, stamens, carpels, and sepals. Due to the presence of both male and female reproductive structures, they are also called perfect flowers. They include the androecium, gynoecium, corolla, and calyx. The modified leaves that surround a flower's base are called sepals.
Ques. What is a whorl in plants? (2 marks)
Ans. The arrangement of sepals, petals, leaves, stamen, carpel, or pistil which extend from a single point is called whorl in plants.
- There are two types of whorls: Accessory and Reproductive whorls.
- Accessory whorls consist of calyx and corolla, whereas androecium and gynoecium are considered reproductive whorls.
Ques. What is a perianth? (2 marks)
Ans. The term perianth describes the entire collection of petals and sepals. The arrangement of perianth inside a flower bud before blooming is known as the aestivation of plants. It consists of floral leaves surrounding the androecium and gynoecium. It forms a cover surrounding the sexual organs, consisting of the calyx, the corolla and the tepals, when called a perigone.
Ques. What is aestivation in flowers? (2 marks)
Ans. Aestivation is the term used to describe how petals and sepals are arranged in flower buds in plants before flowering. There are five types of aestivation which are as follows:-
- Valvate
- Twisted
- Imbricate
- Vexillary
- Quincuncial
Ques. What is the difference between sepals and petals? (3 marks)
Ans. The difference between sepals and petals are as follows:
| Sepals | Petals |
|---|---|
| Sepals are usually green in colour. | Petals are generally bright coloured. |
| They form the outermost part of the whorl. | They form the innermost whorl of the flower. |
| These parts of the flower lack asepalous. | These parts of the flower lack apetalous |
Ques. What is a tepal? (2 marks)
Ans. In certain cases, it is impossible to differentiate between sepals and petals. In those plants, the perianth is formed by the union of the calyx and corolla. Each perianth component is referred to as a tepal. The undifferentiated tepals are also known as "petaloids" because they resemble petals.
Ques. Are sepals involved in photosynthesis? (2 marks)
Ans. Yes, the presence of chlorophyll, a green pigment in sepals, makes them capable of performing photosynthesis. They have a lower density of stomata, which are tiny pores that allow gas exchange (CO2 intake and O2 release) necessary for the process.
Ques. What do you mean by gamosepalous and polysepalous condition? (2 marks)
Ans. The condition when the sepals are fused together, then it is called gamosepalous. Hibiscus or China rose are some common examples of this category. On the other hand, polysepalous refers to the condition in which sepals are free. Rose is the most common example of this category.
Ques. What are the basic units of calyx and corolla? (3 marks)
Ans. Calyx and corolla are together called accessory whorls which help the plants in reproduction.
- Calyx: The basic units of calyx are called sepals. Sepals are typically green, leaf-like structures that enclose the flower bud before it opens. Their primary function is to protect the developing flower.
- Corolla: The basic units of the corolla are called petals. Petals are often brightly colored or fragrant and attract pollinators to the flower. They may also protect the flower's reproductive organs.
Ques. Do sepals always have a green colour? (2 marks)
Since sepals are typically green in colour, they are capable of photosynthesis. But unlike the Gulmohar plants, which have bright-coloured sepals, they are not necessarily green.
Ques. What are the differences between monoecious and dioecious plants? (3 marks)
Ans. The differences between monoecious and dioecious plants are as follows:
| Monoecious Plants | Dioecious Plants |
|---|---|
| When a single plant bears both male and female flowers, the species is referred to as monoecious plant. | Plants having separate male and female flowers are called dioecious plants. |
| Examples include Cucurbits, Coconuts | Common example of dioecious plant are Spinach, door window |
| They are also considered as perfect plants. | In dioecious plants, both male and female structures are not present in the same plant, therefore they are called imperfect plants. |
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