Androecium: The Male Part of a Flower
Androecium is the term used to describe the collective stamens of a flower. Stamens are the structures that produce pollen, which contains the male gametes of angiosperms. The word androecium comes from the Greek words for “man” and “house”, implying that it is the male chamber of the flower.
A stamen typically consists of two parts: a filament and an anther. The filament is a slender stalk that supports the anther, which is a sac-like structure that contains microsporangia. Microsporangia are specialized cells that undergo meiosis to produce haploid microspores. These microspores then develop into pollen grains, which contain the male gametophyte.
The number, shape, size, and arrangement of stamens vary widely among different species of plants. Some flowers have only one stamen, while others have hundreds or thousands. Some stamens are free-standing, while others are fused together or attached to the petals. Some anthers have two lobes, while others have four or more. Some anthers open by slits, while others open by pores or valves.
The androecium plays a crucial role in the reproduction of angiosperms. Pollen grains are transferred from the anthers to the stigma of another flower, either by wind, water, animals, or self-pollination. This process is called pollination. Once on the stigma, the pollen grain germinates and grows a pollen tube that reaches the ovule inside the ovary. The pollen tube delivers two sperm cells to the ovule, where one fertilizes the egg cell and the other fuses with two polar nuclei to form the endosperm. This process is called double fertilization and results in the formation of a diploid zygote and a triploid endosperm. The zygote develops into an embryo, while the endosperm provides nourishment for the embryo. The ovule then matures into a seed, and the ovary into a fruit.
The androecium is one of the four whorls of a typical flower, along with the calyx, corolla, and gynoecium. The calyx is the outermost whorl, composed of sepals that protect the flower bud. The corolla is the next whorl, composed of petals that attract pollinators. The gynoecium is the innermost whorl, composed of carpels that contain the female reproductive organs.
Types of Androecium
The androecium can be classified into different types based on the number, fusion, and position of the stamens. Some of the common types of androecium are:
- Polyandrous: When a flower has many stamens that are free from each other, the condition is called polyandrous. Examples of polyandrous flowers are rose, mustard, radish, etc.
- Monadelphous: When a flower has many stamens that are fused together by their filaments into a single bundle, the condition is called monadelphous. Examples of monadelphous flowers are hibiscus, cotton, lady’s finger, etc.
- Diadelphous: When a flower has many stamens that are fused together by their filaments into two bundles, the condition is called diadelphous. Examples of diadelphous flowers are pea, bean, lupin, etc.
- Polyadelphous: When a flower has many stamens that are fused together by their filaments into more than two bundles, the condition is called polyadelphous. Examples of polyadelphous flowers are citrus, bombax, etc.
- Syngenesious: When a flower has many stamens that are fused together by their anthers only, the condition is called syngenesious. Examples of syngenesious flowers are sunflower, marigold, dandelion, etc.
- Synandrous: When a flower has many stamens that are fused together by both their filaments and anthers into a single structure, the condition is called synandrous. Examples of synandrous flowers are orchids, cucurbits, etc.
- Epipetalous: When a flower has stamens that are attached to the petals, the condition is called epipetalous. Examples of epipetalous flowers are primrose, potato, tomato, etc.
- Epiphyllous: When a flower has stamens that are attached to the perianth (sepals and petals), the condition is called epiphyllous. Examples of epiphyllous flowers are lily, tulip, onion, etc.
- Antipetalous: When a flower has stamens that are opposite to the petals, the condition is called antipetalous. Examples of antipetalous flowers are mustard, radish, etc.
- Antiphyllous: When a flower has stamens that are opposite to the sepals, the condition is called antiphyllous. Examples of antiphyllous flowers are cactus, euphorbia, etc.
- Alternipetalous: When a flower has stamens that alternate with the petals, the condition is called alternipetalous. Examples of alternipetalous flowers are rose, apple, pear, etc.