Stamens or Androecium
• Stamens are the male reproductive parts of a flower. A stamen is made up of two parts, a stalk like filament and a knob like terminal anther. Each anther has two lobes which are attached at the back by a sterile band called connective.
• In majority of angiosperms, anthers are two lobed or dithecous. Each anther lobe consists of two pollen sacs (or microsporangia). Thus a typical dithecous anther is always tetralocular (or tetrasporangiate).
• In members of family Malvaceae, anthers are monothecous. Pollen grains (or microspores) are produced in the microsporangium.
• Sterile and undeveloped stamens are called staminodes.
• Stamens shorter than the flower are termed as inserted. When stamens protrude out of the flower, they are known
as exserted. They may be borne directly on the thalamus or fused with petals (= epipetalous, e.g., Solanum, Petunia) or tepals (= epiphyilous or epitepalous, e.g., Asphodelus).
• Fusion of stamens with a dissimilar organ is called adhesion while fusion with a similar organ is known as cohesion.
Cohesion of stamens
• Adelphous – Stamens are fused by their filaments only; anthers are free. Fusion of filaments may produce a single group (monadelphous e.g., Hibiscus), two groups (diadelphous e.g., Pea), or many groups (polyadelphous e.g., Citrus).
• Synandrous – Stamens are fused by both their filaments as well as anthers e.g., Cucurbita.
Syngenesious (= Synantherous) – Stamens are fused by anthers only; filaments are free, e.g., Helianthus annuus.
• The free stamens are called polyandrous. They may be equal or unequal in length. The two common types of unequal stamens are tetradynamous (four long and two short, e.g., Brassica) and didynamous (two long and two short, e.g., Ocimum).
• Diplostemonous: Stamens of outer whorl alternate with petals (alternipetalous) and stamens of inner whorl lie opposite to the petals (antipetalous). e.g. Murraya exotica, Cassia.
• Ob-diplostemonous : It is opposite condition of diplostemonous. Here, stamens of outer whorl lie opposite to the petals (antipetalous) whereas those of inner whorl alternate with petals (alternipetalous). e.g. Dianthus (Pink), Stellaria.
Fixation of anthers
• The mode of attachment of the anther to the filament varies greatly in flowers. It is of following types:
– Basifixed or innate: Here the filament is attached to the base of the anther, as in mustard, Datura, radish.
– Adnate : Here the filament is fixed to the anther in such a manner that it runs up the entire length of the anther at its backside, e.g., Magnolia, Ranunculus, Nymphaea.
Dorsifixed : The filament is fixed to the dorsal side or back of the anther and anther is immovable, e.g., Hibiscus rosa sinensis, Passiflora, Sesbania, etc.
Versatile : The filament is attached to the middle of the connective so that anther lobes can swing on it freely. e.g., grasses.
Types of connectives
• When the connective is very narrow, so that the two anther lobes lie in close proximity as in Adhatoda, Euphorbia sp. it is called discrete.
• When the connective is broad and the two anther lobes are separated as in Tilia sp. it is called divaricate.
• In Salvia, the connective is highly elongated. Its one end bears a fertile anther lobe while the other end has a sterile anther lobe. It is called distractile.
• When the connective becomes feathery and grows beyond the anther, it is called Appendiculate.
Dehiscence of anthers
• It is of following types:
– Longitudinal: lengthwise slits, e.g., Datura, mustard, Ranunculus, Citrus.
– Transverse: breadthwise slits, e.g., Malva, Althaea.
– Valvular: Wall of anther lobes breaks at places and gets lifted like valves e.g., berberry, camphor.
– Porous: by pores, which appear at the tips (Solatium, tomato) or at base (Cassia).
– Irregular: Anther wall breaks irregularly e.g., Najas. • The longitudinal dehiscence is of three types:
– Laterorse (Lateral): Slits appear on the sides.
– Introrse : Slits are formed towards the inner side or centre of the flower.
– Extrorse : Slits lie towards the outer side of petals.