Effect of pollen age on fruit set, fruit weight, and seed set in three orchid species
The length of time that pollen remains viable after being removed from the anther may be subject to species-specific selection pressures, e.g., when the average transit time between anther and stigma is long, long-lived pollen may be favoured. Flowering plants that provide no reward to pollinators are predicted to have relatively long-lived pollen, because pollinators are less likely to immediately revisit flowers of a nonrewarding species. I studied the effect of pollen age on fertilization success in three species of orchids that provide little or no reward. Pollen was aged 0, 1, 2, 4, or 8 days outside of the anther and then placed on the stigmas of conspecific flowers. I collected and weighed all resultant fruits and used a subsampling technique to determine the number of embryonated seeds per fruit and the percentage of all seeds that had embryos. There was no evidence that pollen age affected fruit set, fruit weight, embryonated-seed number, or percentage of embryonated seeds in two species (Calopogon tuberosus (Linn.) Britton and Pogonia ophioglossoides (Linn.) Ker.). In the third, Cypripedium reginae Walt., 8-day-old pollen produced significantly lighter fruits with fewer embryonated seeds; however, the percentage of embryonated seeds was not affected. Although the pollen of these nonrewarding orchids appears to have an impressive life-span, it is difficult to make comparisons with other species because most previous studies have relied on laboratory tests of viability that appear to have little relation to performance of pollen in the field.Key words: pollen longevity, Orchidaceae, reproductive success.