Abstract:

The genus Impatiens, known as “dicotyledonous orchids”, is of great interest to pollination biologists because of its extremely wide diversity and different types of specialized pollinators. In this study, populations of Impatiens hananensis, endemic to Hainan Island, distributed at three different altitudes were studied. Floral phenology, floral structure, pollen viability and stigma activity, floral visitors and their behavior, and the breeding system were determined. Results showed that the average life span of a single flower was 4.10 ± 0.46 d; the male and female flowers lasted 3.15 ± 0.24 d and 0.95 ± 0.36 d, respectively. The species’ flowering peak was in early August, and the high altitude population flowered the latest. The pollen viability of a single flower appears in the trend of first increased then decreased with the flowering time went on, and reached to the highest on the second flowering day in low and middle altitude populations, and which declined gradually with the flowering time went on in high altitude population. Stigma activity generally rose as flowering time went on, but this measure was lower in high altitude population on different flowering days. The main pollinators were Amegilla leptocoma and A. zonata; A. leptocoma was the main visitor in low and middle altitude populations while A. zonata was in the high altitude population. We observed no automatic self-pollination or apomixis in I. hainanensis, and hand-pollination increased the fruit set (75-90%), compared to the natural situation (40-60%). This lower natural pollination success rate was especially true in the high altitude population where pollination was most limited. Therefore, conservation work with Impatiens hainanensis should protect both habitats and effective pollinators of I. hainanensis in order to promote gene flow via pollinators and seed movement among populations at different altitude via pollinators, and maintain the population genetic diversity and effective population size of Impatiens hainanensis.

Key words: Impatiens hainanensis, endemic species, karst landforms, breeding system, ecological adaptation, dichogamy