Pollination biology of the endangered orchid Cypripedium japonicum in a fragmented forest of Japan

Pollination biology studies of the endangered orchid Cypripedium japonicum were conducted in its natural habitat using pollinator observation and hand-pollination experiments. The observed fruit set was as follows: artificial outcross-pollinated, 100%; artificial self-pollinated, 100%; pollinator-excluded, 0%; and emasculated flowers, 0%. These results show that this species, although self-compatible, is neither autogamous nor agamospermous. The fruit set for open-pollinated flowers was 14.9%, which suggests that the study population was subject to pollinator limitation. The nectarless flowers of C. japonicum were exclusively visited and pollinated by the queens of two bumblebee species (Bombus ardens and B. diversus diversus). It is probable that the nectarless flowers of C. japonicum attract pollinators through a generalized food deceptive system.