Variation in floral sex allocation and reproductive success within inflorescences of Corydalis ambigua (Fumariaceae): pollination efficiency or resource limitation?


G. Kudo (fax + 81 11 7064954;


  • 1The variation of floral sex allocation with flower position within inflorescences was investigated in the spring ephemeral, Corydalis ambigua. Investment in female function (pistil), attraction (corolla) and nectar production decreased from bottom to top flowers, whereas male investment (stamen) did not differ.
  • 2 This self-incompatible species appears to set seeds as a result of visitation by nectar robbing bumblebee queens. The tendency of bees to visit lower flowers first and then move upwards within an inflorescence should result in directional pollen flow from bottom to top flowers.
  • 3 Naturally pollinated upper flowers set fewer seeds than intermediate and lower flowers due to pollen limitation. The lack of differences in seed set and seed mass per pod following artificial outcrossing indicated that resource limitation did not explain the variation in seed production of flowers in different positions. Pollen viability also did not differ significantly between flower positions.
  • 4 A model of pollination was developed that incorporated the visitation pattern of bumblebees and observed variations in nectar distribution between flower positions. This predicted that receipt of outcross pollen would decrease from bottom to top flowers, but that pollen export to other plants would not differ between flower positions provided that the pollen exchange rate of pollinators was either small or positively correlated with nectar content of each flower position. The observed pattern of floral sex allocation would then be parallel to relative success of pollen export and import between flower positions within inflorescences.