Floral sex allocation in a hermaphrodite herb with 1-day flowers, Hosta rectifolia (Liliaceae)

The size-dependent sex allocation theory predicts that a female-based sex allocation is accelerated with increasing resource status in insect-pollinated hermaphrodite plants. However, variations in the mating environment among flowers, which are caused by pollinator movements and temporal fluctuation in the floral sex ratio, may cause diverse patterns in sex allocation among flowers within inflorescences. We examined the floral sex allocation among plants and among flowers within inflorescences in a perennial hermaphrodite species with 1-day flowers, Hosta rectifolia Nakai. Flowering progresses sequentially from basal to distal positions within an inflorescence with little flowering overlap among flowers. At the plant level, both pollen and ovule production per flower increased with plant size. Within inflorescences, both ovule and pollen production per flower declined from basal to distal positions, indicating decreasing resource availability per flower. The probability of fruit-set success under natural conditions also decreased from basal to distal positioned flowers within inflorescences. However, the pollen to ovule ratio of individual flowers remained constant, regardless of floral position and plant size. Constant sex allocation at the flower level is consistent with the prediction of the mating environment theory; every positioned flower seemed to have a similar potential of pollination success because there was no geitonogamous pollination.