Difference Between Unisexual and Bisexual Flowers

Main Difference – Unisexual vs Bisexual Flowers           

Unisexual and bisexual flowers are two types of flowers found in plants. Flowers are the reproductive structures of angiosperms. Both male and female reproductive organs are localized in flower. Pistils are the female reproductive organs, and stamens are the male reproductive organs found in a flower. A mature pistil contains one or more ovules, style, and a stigma. Stamens contain anthers, which are held by filaments. Pollen grains, produced in anthers, are deposited on the stigma during pollination. The germination of pollen grains allows the fertilization of sperm cells with egg cells inside the ovule. Male and female reproductive organs are arranged in flowers differentially and are known as unisexual and bisexual arrangements. The main difference between unisexual and bisexual flowers is that unisexual flowers contain male and female reproductive organs in separate flowers whereas bisexual flowers contain both male and female reproductive organs in the same flower. 

This article explains, 

1. What are Unisexual Flowers
      – Definition, Characteristics, Pollination, Examples
2. What are Bisexual Flowers
      – Definition, Characteristics, Pollination, Examples
3. What is the difference between Unisexual and Bisexual Flowers

Difference Between Unisexual and Bisexual Flowers - Comparison Summary

What are Unisexual Flowers

Unisexual flowers are incomplete flowers, containing either male or female reproductive organs in the flower. That means, androecium, which is the male reproductive structure and gynoecium, which is the female reproductive structure, are found in separate flowers. The flowers containing the androecium are called male flowers and the flowers containing gynoecium are called female flowers. In some plants, both male and female flowers occur in the same plant. These plants are called monoecious plants. Corn is the most common monoecious plant. In dioecious plants, either male or female flowers may occur. Hence, depending on the type of flowers present in the plant, these plants can be divided into two as male plants and female plants. Holly, asparagus, dates, mulberry, ginkgo, persimmons, currant bushes, juniper bushes, sago, and spinach are dioecious plants.

In monoecious plants, both self and cross pollination can occur. In dioecious plants, only cross pollination can occur due to the presence of one types of flowers in the plant. Hence, unisexuality is considered as an adaptation to undergo only cross pollination, which is beneficial over the self pollination. During cross pollination, allogamy occurs, depositing the pollen grain of one plant on the stigma of another plant of the same species. External pollinating agents like water, wind, insects and animals assist cross pollination. Flowers exhibit several characters like brightly colored petals, scents, and nectar in order to attract insects to the flower. The genetic material of two plants is combined during cross pollination, producing a genetically varied offspring to parents.

Difference Between Unisexual and Bisexual Flowers

Figure 01: Corn

What are Bisexual Flowers

Bisexual flowers are complete flowers, containing both androecium and gynoecium in one flower. Therefore, bisexual flowers contain both stamens and pistils in the same flower. Hence, bisexual flowers are called hermaphrodite or androgynous flowers as well.

In bisexual plants, both self pollination and cross pollination can occur due to the presence of both reproductive organs in the same flower itself. During self pollination, the stigma of a plant is pollinated by the pollen grains of a genetically identical flower. Hence, self pollination produces genetically identical offspring to the parent. It occurs in three ways: autogamy, geitonogamy, and cleistogamy. The pollination within the same flower is called autogamy. Geitonogamy is the pollination between different flowers on the same plant. Cleistogamy is the pollination of the flower before its opening.

Main Difference - Unisexual vs Bisexual Flowers

Figure 2: A bisexual flower

Difference Between Unisexual and Bisexual Flowers

Definition

Unisexual Flowers: Unisexual flowers contain male and female reproductive organs in separate flowers.

Bisexual Flowers: Bisexual flowers contain both male and female reproductive organs in the same flower.

Structures

Unisexual Flowers: Male flowers contain stamens whereas female flowers contain pistils.

Bisexual Flowers: A single flower contains anthers and ovary.

Pollination

Unisexual Flowers: Monoecious flowers undergo both self and cross pollination. Dioecious flowers are specialized to undergo cross pollination.

Bisexual Flowers: Bisexual flowers can undergo both self and cross pollination.

Complete/Incomplete Flowers

Unisexual Flowers: Unisexual flowers are called incomplete flowers.

Bisexual Flowers: Bisexual flowers are called complete flowers.

Names

Unisexual Flowers: Unisexual flowers are of two types: monoecious and dioecious.

Bisexual Flowers: Bisexual flowers are called hermaphrodite or androgynous flowers.

Examples

Unisexual Flowers: Flowers in papaya, watermelon, corn and mulberry are the examples of unisexual flowers.

Bisexual Flowers: Flowers in rose, lily, hibiscus, mustard and sweet pea are the examples for bisexual flowers.

Conclusion

Both unisexual and bisexual flowers are involved in the sexual reproduction of angiosperms. Unisexual flowers contain androecium and gynoecium in separate flowers, whereas bisexual flowers contain both androecium and gynoecium in the same plant. Plants containing unisexual flowers can be divided into two as monoecious and dioecious plants. Monoecious plants are capable of undergoing both self and cross pollination due to the presence of both male and female flowers in the same plant. In contrast, dioecious plants only undergo cross pollination. Bisexual flowers can undergo both self and cross pollination due to the presence of both reproductive organs in the same flower; hence, they are called androgynous flowers. However, the main difference between unisexual and bisexual flowers is the presence of male and female reproductive organs in the flower.

Reference:
1. “Adventist Youth Honors Answer Book/Nature/Flowers – Advanced.” Adventist Youth Honors Answer Book/Nature/Flowers – Advanced – Wikibooks, open books for an open world. N.p., n.d. Web. 26 Apr. 2017.
2. “First Book of Indian Botany.” Google Books. N.p., n.d. Web. 26 Apr. 2017.

Image Courtesy:
1. “Maize plant diagram” By LadyofHats – Own work (CC0) via
2. “Ranunculus glaberrimus labelled” By Ranunculus_glaberrimus_(5384213151).jpg: Matt Lavinderivative work: Peter coxhead – This file was derived fromRanunculus glaberrimus (5384213151).jpg: via

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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