Abstract:

In this paper, stamen movement is defined as the movement of stamens with their own energy, either automatically or stimulated by pollinator or other forces, except the forced movement of stamen under the pressure of pollinators. Four main types of stamen movements are classified: stimulated, simultaneous and slow, quick and explosive and cascade. Stimulated movement is normally caused by touching of visiting insects, which can enhance the contact probability of anther/pollen with pollinators or promote contact of anther with self pistil. Simultaneous and slow movement can alter the extent of herkogamy and modify reproductive patterns, and in some plants the stamen can move the anther directly to the self stigma to promote autogamy. Quick and explosive movement can release the pollen rapidly to the air or adhere to visiting insects to promote wind and/or insect dispersal of pollen grains. In cascade movement-in Ruta graveolens (Rutaceae), Tropaeolum majus (Tropaeolaceae), and plants of Loasaceae and Parnassiaceae - the stamens can move one by one and anthers dehisce individually when positioning at the center of flowers. The adaptive significances of cascade movement have not been studied, but, according to ‘pollen presentation theory’, cascade movement can alter the herkogamy and control the pace of pollen presentation and distribute pollen among pollinators by either packaging or dispensing mechanisms, which can greatly enhance pollen removal efficiency. Furthermore, the interferences between stamens and pistil and among individual stamens can be decreased as a result of obvious herkogamy and spatial separation of each stamen caused by cascade movement. In Ruta graveolens, all the stamens move together to the center of flower after the cascade movement, this two-time, multiple-direction stamen movement probably is the most complex stamen movement presently known. Future emphasis in the field of stamen movement should include 1) the effects of stamen movement, especially the cascade movement, on sexual interference and interference among individual stamens, 2) the interaction of stamen movement with dichogamy (temporal separation of male and female funtion) and herkogamy (spatial separation of anthers and stigma), both of which can be modified by stamen movement and 3) the physiology and development of stamen movement.

Key words: dichogamy, herkogamy, pollen presentation theory, pollination, reproductive strategy, stamen cascade movement