Androecium is the third whorl of the flower. It is the essential part and comprises of the male reproductive organs, called the stamens. Each stamen consists of three parts, filament, anther and a connective.
Filament: Filament is the stalk in which the anther is borne. When the filament is not developed, the anther is said to be sessile. The filament is a long slender structure but sometimes it becomes flat and leaf like, as in Nymphaeae (water lily). When the anther is not developed the filament becomes sterile and is known as staminode, example, Cassia, Pterospermum etc. The staminodes may become brightly coloured and petal like (petalloid) as in Zingiber, Canna etc.
Anther: Anther is the most essential part of the stamen. It is borne at the tip of the filament. Usually, it is bilobed. Each lobe has two chambers or loculi, called the pollen sacs. A normal anther has four pollen sacs. Each pollen sac contains a mass of fine powdery granular cells called the pollen grains. The pollen grains are the main reproductive unit or male pores. When the anther bursts, the pollen grains disperse like dust particle. In some exceptional cases, the individual pollen cells do not form pollen grains, but they become united into a mass called the pollinium as in Calotropis.
Connective: It is a continuation of the filament forming a short mid rib-like structure in between the two lobes of the anthers and connecting them together.
Attachment of the filament to the anther:
- Basifixed: When the filament is attached to the anther at its base, the anther is known as basifixed or innate as in Raphanus (radish), Brassica (mustard) etc.
- Dorsifixed: The anther is said to be dorsifixed when the filament is attached at the back of the anther as in Datura, Passiflora, Hibiscus etc.
- Adnate: When the filament is attached to the anther throughout its whole length, the anther is called adnate as in Michelia etc.
- Versatile: The anther is said to be versatile when the filament is attached to the back of the anther at one point, so that it can swing freely in the air, example, Cynodon, Oryza, Triticum etc.
Cohesion of stamens:
Fusion of the members of the same whorl of the flower is known as cohesion. The stamens of a flower may remain free or they may remain united with one another. The degree of cohesion of stamens varies. It mainly takes place in two ways.
- When the filaments of the stamens are fused together but the anthers remain free, the condition is said to be adelphous.
- When the anthers are fused together, but the filaments remain free from one another, the condition is called syngenesious. Accordingly, the following few general types of cohesion of stamens are as follows:
- Monoadelphous: When the stamens are fused together in a single bundle but the anthers remain free, the stamens are said to be monoadelphous, example, Hibiscus, Abelmoschus, Gossypium etc. The filaments are fused together in such a way that they form a tube-like structure called the staminal tube.
- Diadelphous: When the stamens are fused into two bundles, but the anthers are free, the stamens are said to be diadelphous. The flowers consists of ten stamens, of which nine are united into one bundle and the tenth one remains free as in Dolichos, Pisum, Clitoria, Cicer etc.
- Polyadelphous: The stamens are said to be polyadelphous when the filaments are united into more than two bundles and the anthers remain free, example, Citrus, Bombax, Ricinus (castor) etc.
- Syngenesious: The stamens are said to be syngenesious when the anthers are united together but the filaments remain free from one another, example, Tridax, Helianthus, Tagetes, Ageratum etc.
- Synandrous: When both the anthers and filaments of all the stamens fuse together, the condition is said to be synandrous, example, Cucurbita (gourd), Cucumis (cucumber) and other plants of cucurbitaceae family.
Adhesion of stamens:
Adhesion is the attachment of members of different whorls of a flower. In some flowers, the stamens are found to be attached or fused with petals or with the gynoecium. Depending on this, they are described as follows:
- Epipetalous: When the filaments of the stamens are united with the petals up to a certain length and their anthers remain free from one another such petals are said to be epipetalous, as in Solanum melongena, Datura, Vinca, Nerium (oleander) etc.
- Epiphyllous: The stamens are said to be epiphyllous when the filaments are attached or fused with the lobes of the perianth as in Allium (onion), Asparagus, Aloe vera, Polianthes (tuberose) etc.
- Gynandrous: When the stamens are partially or completely adhered to the carpels, they are said to be gynandrous as in Calotropis, Cucurbita etc.
Length of stamens:
The length of stamens of a flower may be equal or may vary without any definite relationship to each other but in some flowers, there exists a definite relation between short and long stamens. The following are the two common conditions of stamens with varying lengths in flowers.
- Didynamous: When there are four stamens of which two of them are long and other two are short, then the stamens are described as didynamous. This condition is found in flowers of Leucas aspera, Ocimum (basil) etc.
- Tetradynamous: Stamens are said to be tetradynamous when the flower has six stamens and out of these, four of them are longer than the other two as in Brassica (mustard), Raphanus (radish).
Number of stamens:
The numbers of stamens vary from flower to flower of different plants. In symmetrical flowers, the number of stamens is equal to the number of sepals or petals or multiple of that. But in asymmetrical flowers, the numbers of stamen varies. Depending on the number of stamen, the androecium may be:
- Monandrous: The number of stamen in this case is only one, example, Zingiber officinale.
- Diandrous: In this case, the flower consists of two stamens, example, Adhatoda.
- Triandrous: The androecium is said to be triandrous when it consists three stamens, example, Triticum aestivum (wheat).
- Tetrandrous: The androecium is said to be when it has four stamens, example, Mimosa.
- Pentandrous: In this case, the flower consists of five stamens, example, Datura.
- Hexandrous: In this case, the flower consists of six stamens, example, Oryza.
- Polyandrous: The androecium is said to be polyandrous when the flower consists more number of stamens, example, Acacia arabica.