Abstract: The floral and pollination biology of Antidesma montanum was studied. The floral phenology, pollen-ovule ratio (P/O), pollen histochemistry, pollen viability, floral visitors and their behavior, and the sexual system were observed and determined. The observation is that Antidesma montanum is a dioecious species with a sexual ratio of ca. 1:1 during anthesis. Results were obtained as follows: (1) A male/female inflorescence consisted of 140.33±27.79/208.33±33.65 (n=6) small (diameter ca. 3.4 mm) light greenish yellow flowers; both male and female inflorescences lasted for ca. 7 days. (2) The longevity of a single flower of A. montanum was 2 days; pollen viability (MTT test) remained at a high level (＞95%) after anthesis; the pollen was starchless; uncalibrated pollen/ovule ratio was 3333.33±607.18; a mesh-netted flower produced up to 0.34?0.03 ?L nectar with 3.69%?0.30% sugar equivalent. (3) The floral design and floral display were well adapted to fly pollination. (4) The effective pollinators were dipteran insects Chrysomya megacephala (Calliphoridae), Chrysomya sp., Drino sp. (Tachinidae), Spilogona sp. (Muscidae), and Mitroplatia sp. (Muscidae), which visited both male and female flowers for nectar. The sweet scent emitted during anthesis was a direct attraction to pollinators. No fruit set in bagged flowers indicated that there was no apomixis. No significant difference was found in fruit sets between flowers with open pollination (36.7%) and hand supplemental pollination (39.1%), suggesting that the fruit set was determined by its resource limitation. The correlations between fly pollination and the diclinous sexual systems, and between fly pollination and plants with small greenish yellow flowers were also discussed.

Key words: Antidesma montanum, dioecy, fly pollination, Diptera, Euphorbiaceae