Essential Parts of Flower: Androecium

Androecium: The male reproductive organ

Male reproductive unit: Stamen

• The third whorl of flowers is the male reproductive part of the flower.
• It is composed of stamens (microsporophylls).
• A stamen is an angiosperm's male reproductive unit.
• A typical stamen differentiates into three parts - Filament, Anther, and Connective.

Structure of Stamen

1. Filament - The long and slender stalk is called the filament. The proximal end of the filament is attached to the thalamus or the petal of the flower.
2. Anther - The anther is a bilobed structure with each lobe containing four pollen sacs or microsporangia. Anther typically contains two com­partments called thecae (singular theca). Each theca consists of two microsporangia. Two microsporangia fused to form a locule.
3. Connective - Anther and filament are attached together with the help of a small region, called connective. Connective contains vascular tissues.

• Sterile stamens are called Staminodes. Example: Cassia.
  (i) Distinct: stamens which do not fuse to one another.
  (i) Free: stamens which do not fuse with other parts of flower.
  (iii) Apostemonous: flowers with stamens that are free and distinct.

Fusion of Stamens:

• The fusion of stamens fusing among themselves or with other parts of flower.
• They are of two types - Connation and Adnation

1) Connation: Refers to the fusion of stamens among themselves. It is of 3 types - Adelphy, Syngenecious, and Synandrous.

1. Adelphy: Filaments connate into one or more bundles but anthers are free. It may be the following types. 
   (i) Monadelphous: Filaments of stamens connate into a single bundle. Example: Malvaceae (China rose, Cotton).
   

   Monadelphous

   
   (ii) Diadelphous: Filaments of stamens connate into two bundles. Example: Fabaceae (pea) and Clitoria.
   

   Diadelphous

   
   (iii) Polyadelphous: Filaments connate into many bundles. Example: Citrus, Bombax
   

   Polyadelphous

2. Syngenesious: Anthers connate, filaments free. Example: Asteraceae.
   

   Syngenesious

3. Synandrous: Filaments and anthers are completely fused. Example: Coccinea.

2) Adnation: Refers to the fusion of stamens with other floral parts.

1. Epipetalous: Stamens are adnate to petals. Example: brinjal, Datura.
   

   Epipetalous

2. Episepalous: stamens are adnate to sepals. Example: Grevillea (Silver oak)
3. Epitepalous (epiphyllous): stamens are adnate to tepals. Example: Asparagus.
4. Gynostegium: Connation product of stamens and stigma is called gynostegium. Example: Calotropis and Orchidaceae.
5. Pollinium: Pollen grains are fused together as a single mass. Example: Calotropis

Arrangement of stamens relate to length of stamens:

1. Didynamous: Four stamens of which two with long filaments and two with short filaments. Example: Ocimum
2. Tetradynamous: Six stamens of which four with long filaments and two with short filaments. Example: Brassica.
3. Heterostemonous: stamens are of different lengths in the same flower. Example: Cassia.

Anther types:

1. Monothecal: One lobe with two microsporangia. They are kidney-shaped in a cross-section. Example: Malvaceae
   

   Monothecal

2. Dithecal: It is a typical type, having two lobes with four microsporangia. They are butterfly-shaped in cross-section. Example: Solanaceae.
   

   Dithecal

Anther attachment:

1. Basifixed: (Innate) Base of anther is attached to the tip of filament. Example: Datura.
   
   

   Basifixed

    
2. Dorsifixed: Apex of filament is attached to the dorsal side of the anther. Example: Hibiscus.
   

   Dorsifixed

3. Versatile: Filament is attached to the anther at midpoint. Example: Grasses.
   
   

   Versatile

    
4. Adnate: Filament is continued from the base to the apex of anther. Example: Nelumbo
   

   Adnate