Spatial separation of stamen and stigma (herkogamy) is an effective way for angiosperm species to reduce sexual interference and prevent self-pollination. It can however also reduce the possibility of pollinators contacting both sexual organs. Floral mechanisms aiming to resolve this conflict have seldom been explored.   

The research group, led by Prof. YANG Chunfeng from Wuhan Botanical Garden, studied the floral biology of Ajuga decumbens to uncover how the floral mechanism resolved the herkogamy dilemma. 

In the flower of A. decumbens, the stamen and stigma exchanged their position by movement in opposite directions with floral development. The movement of the stamen and stigma in opposite direction resulted in position exchange at male and female floral phases. The interactions of dynamic herkogamy and dichogamy not only completely avoided sexual interferences, but also ideally maintained pollination accuracy. 

In Ajuga, the floral morphology might be evolved in response to the changes in pollination environment. This novel floral mechanism contributes significantly to the understanding of the evolution of herkogamy. 

This work was supported by the National Natural Science Foundation of China and published on SCI journal AoB PLANTS entitled “Accurate position exchange of stamen and stigma resolves the herkogamy dilemma in a protandrous plant,Ajuga decumbens(Labiatae)”.   

Floral morphology and inflorescence trait of Ajuga decumbens. A to D indicates male phase, middle phase, female phase and witling phase respectively, while E shows the inflorescence trait (Image by YE Zhongming )