POLLINATION SYSTEMS OF SYMPATRIC IPOMOEA HEDERACEA AND I. PURPUREA AND THE SIGNIFICANCE OF INTERSPECIFIC POLLEN FLOW

Mathematical models estimated that xenogamy accounted for 7% and 35% of the stigmatic pollen loads of Ipomoea hederacea and I. purpurea, respectively, in experimental populations. The xenogamy estimate for I. hederacea agreed closely with outcrossing estimates previously reported for this species. The discrepancy between the xenogamy estimate and the previously reported outcrossing estimate for I. purpurea could be explained by differing pollinator flight patterns between experimental and natural populations and/or by selection for cross pollen in the pistil of I. purpurea. Interspecific pollen flow from I. purpurea to emasculated flowers of I. hederacea reduced seed production in the latter. The possible significance of interspecific pollen flow from I. purpurea for the evolution of autogamy in I. hederacea was discussed.