Stamen Origin and evolution from foliar to reduced condition

Stamen Origin and evolution:- The stamen is the male reproductive organ in angiosperms. It is also known as androecium or microphylls. The stamen composed of slender stalk with a supporting knob. Each anther consists of two lobes connected by a connective. Each anther has two pollen sacs placed longitudinally. The pollen chamber represents a microsporangium that contains many microspores. Each stamen consists of two parts- filament and anther. Some morphologists believed that the stamen consists of three parts-filament, anther and connective. Filament is the midrib, while anther is formed by the union of the margins of the foliage leaves. Various interpretations have been advanced from time to time regarding the morphology of the stamen.

Classical view:- Goethe proposed that flowers are like abbreviated vegetative leaves. De Candolle

further elaborated the theory and stated that the stamens and carpels are all similar to leaves. Thus,

the individual stamen is a leaf which has been modified to form a reproductive organ. The anther

represents the lamina and the filament is the midrib and the whole structure may be a set of

modification of lamina. Arber and many other reported the homology of stamen parts with the foliage

organs.

Telome theory:- Wilson stated that Goethe’s hypothesis is lacking palaeobotanical evidences.

According to him no theory of the origin and morphology can be established based on assumption

without fossil evidences. Various studies led to the view that the body of early land plant was the

branched axis. The proximal portion becomes differentiated into an absorbing organ and the distal

organs evolves a fertile and sterile branched system. These systems probably grow dichotomously,

and sporangia are formed terminally. Based upon the fact, the foliar organs and other parts of the

angiosperms derived from the sterile branched system and the essential parts the flower from the

fertile system. Accordingly, the modern system came into being as a result of extensive reduction and

specialization of fertile dichotomous branched system. The four celled anther of the angiosperm

stamen is explained by he reduction of ultimate and penultimate branch and then by fusion give rise

to paired sporangia. Wilson though believed that the stamen has evolved from dichotomous system,

yet the final evidence is lacking. However, he forwarded his opinion as the Goethe’s hypothesis is

rational.

Revolutionary view:- Thomson put forwarded another views on the ontogeny of the flowers.

According to him the flower is essentially a heterogenous fertile axis bearing floral parts in the torso.

The base is sterile and produces bracteole, bracts and sepals. Rest of the superficial axis is potentially

sporogenous which give rise to petals, staminode, stamens and carpels. Work of Thomson is opened

for memoir of interpretation. According to Hunt, the stamen is not homologous to entire leaf but a part of leaf and the term sporophyll may not be applied to modern stamen.

Note:- Reviewing all the theories proposed so far, the classical theory looks more convincing, as it stated that flower is a modified shoot and the stamen is a part of it.