Androecium: Definition, Components and Types

Androecium is the male reproductive organ in a flower. It is found in the stamen of the flower and is made up of two parts anther and filament.

• Anther is a yellowish sac-like structure responsible for pollen production.
• Filament has a very thin structure that sustains the anther.
• Plants have their reproductive structures in the flowers.
• The number of petals, sepals, stamens, and pistils can vary amongst plants and can comprise all-female parts, all-male parts, or both.

Let’s have a closer look at androecium, its components, and the different types.

Key Terms: Androecium, Pollen grain, Flowers, Stamen, Polyandrous, Filaments, anther wall layer, Epidermis, Cell wall, Cytoplasm

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What is Androecium?

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“The androecium is the male reproductive component of the flower and is made up of stamens.”

There are four whorls in a flower. These are

• Calyx
• Corolla
• Androecium
• Gynoecium

The androecium is the third whorl in a flower and emerges from the corolla's inner side.

• An anther and filament are also parts of a stamen.
• The anthers seen inside the bloom are usually bilobed.
• Two microsporangia are seen in each lobe of the anther which are also known as pollen sacs that form pollen grains.

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Components of Androecium

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The androecium is made up of stamens. Each stamen consists of two main parts: anther and filament.

• The anther is a bilobed structure at the end of the flower.
• A long, slender stalk called the filament supports the anther and connects it to the flower's receptacle.
• The two anther lobes are separated by a large groove towards the front and joined together by a connective band of tissues.
• An anther has a tetragonal structure with four sides.
• Each of its two lobes contains two microsporangia, located at the corners, making a mature anther tetrasporangiate.
• These microsporangia develop into pollen sacs filled with pollen grains.
• Each microsporangium is roughly spherical and contains primary sporogenous cells.
• These cells form a homogeneous mass of meristematic tissue enclosed by the anther wall.
• They eventually divide to become microspore mother cells.

Anther Wall Layer

The anther wall is composed of four different layers. They are as follows:

Epidermis

The epidermis is the anther's outermost layer. It is a single layer that functions as a protective barrier. Exothecium is a fibrous thickening that occurs in some plant species, such as Arceuthobium.

Endothecium

Alpha-cellulose fibrous bands can be found in the cells of the endothecium layer. These bands emerge from the anther's inner tangential walls and aid in its dehiscence. This is due to their hygroscopic properties. These bands are not present in hydrophytes.

Middle Layer

These are transitory cells. They have 1-3 layers and deteriorate as they grow older.

Tapetum

The innermost layer of the anther wall is called the tapetum.

• The sporogenous tissue is surrounded by this layer.
• These cells provide sustenance to the pollen grains.
• These cells have several nuclei and a lot of cytoplasm.
• These cells are polyploid because they have more than one nucleus that increases DNA content.
• Endomitosis, Restitution nucleus, and Polyteny all contribute to the increase in DNA content.

Pollen Grain

The male gametophyte, or androecium are called pollen grains.

• Pollen grains are spherical structures with a diameter of 25-50 micrometers.
• Their cell wall is referred to as sporoderm and is made up of two layers called exine and intine.

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Types of Androecium

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The different types of androecium are given below

• Monandrous: Flowers with only one stamen are called monandrous. Euphorbia, for example, has only one stamen.
• Diandrous: Flowers with two stamens are called Diandrous. Coronopus, for example, has two stamens.
• Triandrous: Flowers with three stamens are called Triandrous. Triticum, for example, has three stamens in its flowers.
• Tetrandrous: Flowers with four stamens are called Tetrandrous. Scoparia, for example, has four stamens.
• Polyandrous: Flowers with five or more free stamens are called Polyandrous. Corchorus, for example, has a lot of stamens and they're all free.
• Monadelphous: When all of the filaments are fused to create a single tube, yet the anthers remain free, as in Hibiscus.
• Diadelphous: When filaments are grouped while the anthers remain separate, as in Lathyrus.
• Polyadelphous: When filaments are grouped, yet their anthers remain free, as in Ricinus, Citrus, and other plants.
• Syngenesious: When all anthers are grouped with their filaments free, as in the Asteraceae family.
• Synandrous: When all anthers and filaments come together to form a single group, such as in Cucurbitaceae members.
• Antipetalous: Flowers with stamen on the opposite side of the petals. For example, Coriandrum.
• Antiphyllous: Flowers that have stamens on the opposite side of the tepals. For example, Chenopodium.
• Alternipetalous: When stamens are arranged in a pattern that alternates with the petals.
• Epipetalous: When stamens are linked to the petals of a flower, such as a Petunia.
• Episepalous: When stamens and sepals are fused, as in some Verbena species with no petals.
• Epiphyllous: When a flower’s stamens are united with tepals. For example, Asparagus.

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Things to Remember

• There are four whorls in a typical flower. Calyx, corolla, androecium, and gynoecium are the four parts of the flower.
• The androecium is the flower's male reproductive component and is made up of stamens.
• An anther and filament are the parts of a stamen.
• The anther is a bilobed structure at the end of the flower.
• The filament, a long, slender stalk, supports the anther at the top of the stamen.
• The four walls of the anther are the epidermis, endothecium, middle layer, and tapetum.
• The male gametophyte, or androecium, is represented by pollen grains.
• The cell wall of the pollen grains is referred to as sporoderm.