Chin J Plant Ecol ›› 2009, Vol. 33 ›› Issue (1): 222-236.DOI: 10.3773/j.issn.1005-264x.2009.01.024

• Review • Previous Articles    

INTRAFLORAL STAMEN DIFFERENTIATIONS AND THEIR ADAPTIVE SIGNIFICANCES

REN Ming-Xun()   

  1. Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China
  • Received:2008-05-21 Accepted:2008-07-08 Online:2008-05-21 Published:2009-01-30

Abstract:

Intrafloral stamen differentiations have adaptive significances and possible effects on plant reproduction strategies and mating patterns. Intrafloral stamen differentiations, in which stamens in a flower differ distinctly in shape, size or color of filament and/or anther and normally in function, can be classified into five main types: filament differentiation (e.g., filament length differentiation), anther differentiation (e.g., differentiation in pollen viability and anther color or size), differentiation in growth pattern of stamens (e.g., some stamens grow fused and others separately), differentiations in stamen movement (e.g., stamens move at different time and are in different dehiscence stages and different spatial position), and staminodes (i.e., some stamens have lost the function of producing viable pollen and normally have a different shape). Heteranthery, which is mostly found in enantiostylous species with mirror-image flowers, is a special type of stamen differentiation in which filament length, anther size and color, and pollen viability all are so differentiated that the two kinds of stamens show different functions: feeding stamens (normally sterile, but provide nutrients that attract and feed pollinators) and pollinating stamens (produce viable pollen). In some special types of complex breeding systems such as heterostyly and enantiostyly, intrafloral stamen differentiations are also present and differentiation modes often differ among individuals. Intrafloral stamen differentiations cause various spatial positions of anthers in a single flower, which can affect the herkogamy (spatial separation of female and male organs) and dichogamy (temporal separation of female and male functions), and the modes and foraging activities of pollinators can also be greatly affected. Consequently, plant mating patterns such as levels of selfing and sexual interferences are modified. Stamen differentiation can increase plant fitness through presenting pollen in many small doses in differentiated stamens, which can greatly enhance pollen output in plants receiving many pollinator visits, as suggested by pollen presentation theory. So, intrafloral stamen differentiations can be seen as a kind of pollen packaging and dispensing mechanism. Some adaptive significances of stamen differentiations have been recognized, but specific functions of some types (e.g., monodynamous stamens, differentiations in stamen movement time and/or mode, and trimorphic differentiation of stamen in Commelinaceae and some plants of Fabaceae) need further illumination.

Key words: herkogamy, heteranthery, monodynamous stamens, stamen movement, pollination, pollen presentation theory (PPT)