Floral structure and pollination in relation to fruit set in cynanchum otophyllum schneid

We studied the floral morphology and floral biology of Cynanchum otophyllum Schneid in experimental plots and field sites. Some observations were augmented by laboratory studies of floral traits, including scanning electron microscopy and light microscopy. The flower was characterized by a staminal corona. The pollinia were lodged in sacs on each side of the stigma and needed pollen vector for fruit production. C. otophyllum has characteristics similar to bee-pollinated plants. Honeybees (Apis cerana Fabricius) were the main pollinators. Pollinaria removal and pollinia insertion rates were low at 5.4% and 0.45%, respectively. The fruit set was only 2.2% in natural population. The flowering span of C. otophyllum was about 3 months, and the functional longevity of individual flowers was 6–8 days. The extended period may be related to the relatively low levels of effective pollinator activity. The flowers were self-incompatible. Umbels displayed open flowers for 9–10 days, and there was a large overlap in flowering time within and among inflorescences in a single plant. Therefore, a high level of self-pollination is possible. From the significant increases in fruit set in cross-pollinated flowers (12.6%) compared with self-pollinated flowers (1.52%), the low fruit set in C. otophyllum could be partially explained by pollen limitation.