Aims Bulbophyllum ambrosia is an epiphytic orchid growing on rocks and trees in limestone seasonal rainforests and is commonly distributed in southern China. We found no fruit set of B. ambrosia during long-term monitoring of species diversity, reproductive phenology and pollinators of local orchid species in Green Stone Forest Park. Our objective was to determine barriers to fruit set in B. ambrosia.
Methods Flowering phenology and natural fruit-set were monitored once a week for three years. Floral morphology was studied during flowering time. We also investigated the rate of pollinia removal and deposition over two flowering seasons. To determine the self-compatibility system, different hand-pollination treatments were conducted over three years at the study site. We also observed floral visitors for 150 h over two years.
Important findings Unlike other myophilous species in the genus, B. ambrosia is fragrant and presents nectar as reward. Observations of floral visitors showed that honeybee (Apis cerana cerana) was the only efficient pollinator and regularly visited flowers with high frequency. In natural populations, the rates of pollinia removal and deposition were high, but there was no fruit set. The hinged labellum plays an important role in the process of honeybee pollination of B. ambrosia. No fruit was found in the selfing pollination treatment, and fruit set of crossing pollination treatments was >90% over two years, suggesting that B. ambrosia is self-incompatible. To our knowledge, this is the first report of a self-incompatible species in Bulbophyllum. Individuals of B. ambrosia have a mass of flowers opening simultaneously during anthesis because of its strong ability in cloning. Honeybees visited 4.29 ± 0.40 flowers ( n = 66) in average per visitation, which may lead to geitonogamy. Self-incompatibility causes no fruit set as the result of geitonogamy. These results provide useful implications for future conservation of B. ambrosia.