Pollination ecology of Impatiens uliginosa (Balsaminaceae) endemic to China

China is one of the five major distribution regions of Impatiens in the world, with more than 270 species distributed all over the country, especially in limestone areas such as Yunnan, Guizhou and Guangxi. In order to explore pollination ecology of Impatiens uliginosa, we conducted the following experiments: observing the floral traits and floral phenology, measuring the nectar volume and sugar concentration, counting pollen viability, deposition and removal, carrying out pollination treatments and recording floral visitors and their behavior. Results show that the average life span of a single flower is 3.23 +/- 0.68 d. The male and female phase lasted for 1.70 +/- 0.06 d and 1.53 +/- 0.63 d. The amount of nectar per flower is 6.97 +/- 0.47 ul and sugar concentration of nectar is 36.58 +/- 0.82%, respectively. Stigma is receptive on the first day of anthesis. Pollen viability is strongest on the second day of anthesis. The pollen-ovule ratio (P/O) is 3974.28 +/- 105.07. We investigated the contributions of different floral visitors. Bombus sp., Apis dorsata, Lobocla proxima, Ant sp. and Ephydra sp. are diurnal visitors. However, Bombus sp. is the most effective pollinator of I. uliginosa. Pollination treatments indicated that I. uliginosa is self-compatible but completely relies on pollinators for pollination. There is no restriction on pollination in the field and I. uliginosa can avoid inbreeding depression. This study is of great significance to enrich the biological data of pollination and protect the biodiversity of Impatiens.