What is the Difference Between Sepals and Petals

The main difference between sepals and petals is that sepals are the green colour, leaf-like structures that form the outermost whorl whereas petals are the bright-colored petaloid structures which form the inner whorl. Furthermore, sepals are responsible for protecting the inner parts of the budding flower while petals are responsible for attracting pollinators and protecting reproductive structures.

Sepals and petals are two non-reproductive structures in a flower. However, they aid in the sexual reproduction of flowering plants.

Key Areas Covered

1. What are Sepals
     – Definition, Structure, Function
2. What are Petals
     – Definition, Structure, Function
3. What are the Similarities Between Sepals and Petals
     – Outline of Common Features
4. What is the Difference Between Sepals and Petals
     – Comparison of Key Differences

Key Terms

Calyx, Corolla, Flower, Petals, Pollinators, Sepals

What are Sepals

Sepals are the green color, leaf-like structures, enclosing the flower bud. They are responsible for protecting the flower bud from injuries and weather during its growth. Moreover, they support petals when blooming. Therefore, sepals form the outermost whorl of a flower and it is known as the calyx. The form and the development of sepals vary among plants. Some sepals occur free (polysepalous) or are fused together (gamosepalous).

Figure 1: Perianth of a Mature Flower

Furthermore, some sepals fuse together to form a calyx tube. Some flowers have sepals and petals with the same colour and are indistinguishable. These are known as tepals. However, after flowering, sepals are useless and they wither or become vestigial. But, some sepals keep alive to protect the fruit.

What are Petals

Petals are the modified leaves that surround the reproductive structures of the flower. They are petaloid and have bright colours. Therefore, the main function of petals is to attract pollinators to the flower. Moreover, they protect the reproductive structures in the flower. Altogether, petals are known as the corolla. Corolla is the whorl which generally occurs inside the calyx.

Figure 2: Sepals and Petals of a Rose Bud

Same as the sepals, the form and the development of petals widely vary among plants. In general, flowers of eudicots (the largest group of dicots) most frequently have four or five petals while flowers of monocots have three or six petals. Most flowers are symmetrical only in one particular plane. Also, petals have two parts; the upper, broad, leaf blade-like blade and the lower, narrow, petiole-like claw. Some flowers contain all symmetrical petals while others contain asymmetrical petals.

Similarities Between Sepals and Petals

• Sepals and petals are two types of non-reproductive structures in a flower.
• They are collectively known as perianth.
• Both are responsible for protecting the reproductive structures of a flower.
• Also, both are modified leaves.
• Moreover, the number of sepals or petals in a flower is its merosity. The merosity of a eudicot flower is typically four or five while the merosity of a monocot or palaeodicot flower is three, or a multiple of three. Thus, this is one form to classify flowers.

Difference Between Sepals and Petals

Definition

Sepals refer to each of the parts of the calyx of a flower, enclosing the petals and typically green and leaf-like while petals refer to each of the segments of the corolla of a flower, which are modified leaves and are typically coloured. Thus, this is main difference between sepals and petal.

Colour

Sepals are green in colour while petals have bright colours.

Structure

Moreover, another easily visible difference between sepals and petal is that sepals are leaf-like while petals are petaloid.

Whorls

Furthermore, sepals form the outermost whorl of the flower while petals form a whorl inner to the sepals.

Forms

The whorl of sepals forms the calyx while the whorl of petals forms the corolla. Hence, this is another difference between sepals and petal.

Function

The main function of sepals is to protect the inner structures of a flower bud while the main function of petals is to attract pollinators to the flower.

In Absence

Flowers without sepals are known as asepalous while flowers without petals are known as apetalous.

Conclusion

Sepals are the outermost whorl of the flower. They are leaf-like and green in color. They form the calyx. The main function of sepals is to protect the inner structures of a flower bud. On the other hand, petals are the inner whorl of the flower to the sepals. Moreover, they are bright in color and are responsible for attracting pollinators. However, both sepals and petals are non-reproductive structures of a flower. The main difference between sepals and petals is their structure and function.

Reference:

1. “Characteristics of Flowers (Theory).” Amrita Online Lab, Amrita.olabs.edu.in, Available Here.

Image Courtesy:

1. “Mature flower diagram” By Mariana Ruiz LadyofHats – Own work (Public Domain) via Commons Wikimedia   
2. “Rose-Bud-Beautiful-Garden-Pink-Nature-Flower-4012590” (CC0) via Max Pixel