[Objective] The aim of this study was to investigate spontaneous self- pollination mechanism of Asarum sieboldii. [Methed] Through field observation and manual controlling test under the cultivated condition, the whole flowering process of Asarum sieboldii belonging to Asarum subgenus Heterotropa was thoroughly ob- served to investigate its pollination mechanism. [Result] Asarum sieboldii is a kind of species dominated by spontaneous self-pollination. Its female flower became mature firstly, and the duration of single flower ranged from 3 to 4 d. The first day was fe- male phase duration, and the stigmas could receive foreign pollen, while stamen fila- ments bent down towards the base of calyx tube with 90°, and anther had no crack. During the following 2 days, two cycles of stamens erected subsequently, while an- thers became dehiscent and naturally contacted with stigma at the same time, so spontaneous self-pollination was finished. Artificial self-pollination and out-crossing test had proved that the out-crossing of Asarum sieboldii were all fertile with seed setting rate of 100%. Emasculation by bagging test had suggested that Asarum sieboldii had no parthenocarpy and apomixes. [Conclusion] Asarum sieboldii belongs to sub- genus Heterotropa, but its pollination mechanism is similar to that of subgenus Asarum.
