The epidermal cells of flowers have been studied in their morphological traits, functions, and evolutionary backgrounds. However, the morphological changes of the cells during flowering and the ecological importance of the changes remain largely unknown. Here, we report that the flower surface microstructure composed of conical epidermal cells present at the female phase disappear during the male phase, and that the changes control the trap and release of the pollinators in protogynous trap flowers of Aristolochia liukiuensis, and Aristolochia shimadae.
  Previous studies on trap pollination in other plant groups have indicated that the presence of conical epidermal cells obstructs insects from walking on the flowers. To evaluate the correlation between the microstructure and the trap function of the flower, we collected the flowers with or without the microstructure at different phases and checked the number of trapped flower visitors. To examine if the presence/absence of the microstructure affect the behavior of pollinators, a pollinator was introduced into a fresh flower in which the nectary had been cut off, and we checked if the pollinator could escape from the flower within 2 hours. The results suggest that the microstructure play a primary role in the trap pollination of the plant species.