Abstract: [Objective]Lageratroemia indica is a typical species for studies on flower color polymorphism and heteranthery due to the fact that it has different colors (red, purple and white) and two distinctively different types of stamen. Floral syndrome and breeding systems of L. indica have been examined to explore reproductive strategies of different color morphs and roles of two types of stamen in pollination. [Method]We conducted field investigations,pollination surveys, artificial pollinations and bag experiments on floral syndrome, flowering course, pollination pattern and functional floral morphology of three floral morphs of L. indica in Zhoushan Forest Park (112°22'46″E, 34°37' 37″N), Luoyang, China. [Result]1) The flowering phenology and the flowering dynamic of individual flower of the three floral morphs were similar (The life span of the latter was about 4-5 days). 2) There were differences in floral morphology of the three, that is, diameter of flower, anther length and filament length of the longer stamens. 3) The number of short stamen differed among the floral morphs (P<0.05): white morph>purple morph>red morph. Pollen grain number and P/O ratios of the red morph were significantly less than the other two (P<0.05). 4) The dynamic trends of pollen viability and stigma receptivity were similar. Stigma receptivity and pollen vitality had a period of overlap. The peak of pollen vigor of long stamen was prior to the optimal stigma receptivity whereas the peak of pollen vigor of short stamen overlapped the optimal stigma receptivity. The optimal stigma receptivity of white morph and purple morph lasted two hours more than that of the red morph. 5) There were significant differences between the two types of stamen in shape, color, number of pollen grains, fruit set and seed number following experimental treatments with stamens removed, and differences also existed in pollinator behavior. The differences suggested that there was function differentiation of the two types of stamen, i.e., the yellow anthers were to attract pollinators and satisfy the insects' demand for pollen while the dark yellow anthers were to satisfy plant's need for safe gamete transport. However, there were no differences in pollen viability, histochemistry, and fruit set following artificial pollination experiments between the two types of stamen, suggesting that there was no physiological differentiation between them. The anther-removal experiment also indicated that the arrayal shape of stamens affected the extent of functional differentiation of the two types of stamen. 6) P/O ratio (P/O ratio was 1 580-2 262), all the pollination surveys and bag experiments indicated that there was no apomictic, spontaneous autogamy and self-incompatibility, and that the breeding system of L. indica was mainly facultative xenogamy. 7) The red morph was the mostly visited and pollinators exhibited significant preference for it over the other two(P<0.01). The fruit set rate and seed number of white and purple morphs increased after artificial pollination. [Conclusion]There was pollen limitation in white and purple morphs under natural conditions. Therefore, increasing investment in male functions and prolonging optimal stigma receptivity may be adaptive strategies to sustain reproductive success. During pollination process, two types of stamen worked both individually and cooperatively. Anthers of the two types of stamens started to dehisce at different time and the viability of pollen lasts for different durations. This pollen packaging mechanism may be the reproduction strategy for L. indica to improve the efficiency of pollination exportation.

Key words: Lagerstroemia indica, heteranthery, mating system, floral morphology, pollinator preference