INTERFERENCE THROUGH IMPROPER POLLEN TRANSFER IN MIXED STANDS OF IMPATIENS CAPENSIS AND I. PALLIDA (BALSAMINACEAE)

Abstract

Mechanisms of interference through improper pollen transfer are described for sympatric populations of the simultaneously flowering annuals Impatiens capensis and I. pallida. Stigmas of both Impatiens species are receptive to conspecific pollen from the time of androecium disarticulation until after perianth drop. Pollen of I. pallida adheres to, and germinates on, the stigmas of I. capensis. The pollen tubes reach the ovules but do not fertilize them. In contrast, pollen of I. capensis adheres poorly to I. pallida stigmas and fails to germinate. Pollen mixtures of the two Impatiens species cause a much greater reduction in fruit set in I. capensis than in I. pallida. Despite the interference of I. pallida pollen, I. capensis persists in mixed populations with I. pallida by: 1) possessing stigmas receptive to pollen throughout the female phase; 2) having the ability to produce a full seed complement via one pollination event; and 3) possessing cleistogamous flowers to ensure sexual reproduction.