Anther appendages of Incarvillea trigger a pollen-dispensing mechanism.

BACKGROUND AND AIMS Anther appendages play diverse roles in anther dehiscence and pollen dispersal. This study aims to explore the pollen-dispensing mechanism triggered by special anther appendages in Incarvillea arguta. METHODS Field studies were conducted to record floral characteristics, pollinator visitations, and flower-pollinator interactions. Measurements of flowers and pollinators were analysed statistically. Pollen counts following a series of floral manipulations were used to evaluate pollen dispensing efficiency and function of the anther appendages. KEY RESULTS Field observations determined that two species of Bombus (bumble-bees) were the primary pollinators of I. arguta with a mean visiting frequency of 1.42 visitations per flower h(-1). The results display a diminishing pollen dispensing pattern; the proportion of remaining pollen removed by pollinators decreased from 27 % to 10 % and 7 % in subsequent visits. Anther appendages act as a trigger mechanism to dispense pollen. The arrangement of the anthers and appendages function to control pollen load and timing. Mechanical stimulation experiments revealed that one set of appendages is only triggered by stimulation in the direction moving into the flower, while the other set is only triggered by stimulation in the opposite direction (exiting the flower). CONCLUSIONS The anther appendage is a pollen-dispensing trigger mechanism. The configuration of the stamens and duel trigger system has evolved to allocate pollen in allotments to enhance male function.