The Function of the Partially‐Opened Spathe of <i>Pinellia pedatisecta</i> (Araceae) as a Pitfall Pollinator Trap

ABSTRACT In the protogynous genus Pinellia , pitfall trap inflorescence typically attracts flies to the trap entrance using a floral odor, directing them into a spathe tube with a slippery surface covered by downward‐pointed microstructures and imprisoning them near the female floral zone surrounded by the chamber structure (female phase). After pollen shedding, trapped insects are released as the chamber unfolds (male phase). Pinellia pedatisecta is an exception as it lacks a chamber structure. This species unfolds the whole spathe, and shows a high fruiting rate without pollinators. However, its spadix appendix, mostly wrapped by the spathe, emits a floral odor during the initial flowering phase, suggesting that the partially‐opened cylindrical spathe functions as an ephemeral pitfall trap and that the completely unfolded spathe releases insects. To validate this hypothesis, we examined whether spathe unfolding coincided with pollen shedding (Experiment A), trapped insects could escape from the cylindrical spathe fixed by taping (Experiment B), and the microstructure of P. pedatisecta resembled that of its congeners with pitfall traps (Experiment C). Experiment A demonstrated phenological matching between the unfolding movement and male phase. Experiment B revealed that insects were more frequent in taped inflorescences than in the controls. The inner wall of the spathe was covered by downward‐pointed microstructures in P. pedatisecta and two Pinellia species (Experiment C). Therefore, the simplified spathe of P. pedatisecta seemed to perform a similar pollination process as the specialized spathe of congeners, although the unfolding movement pattern differed considerably.