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Keywords:

  • Cyperaceae;
  • dicliny;
  • geitonogamy;
  • monoecy;
  • protogyny;
  • wind pollination

Summary

  • • 
    Monoecy and protogyny are widespread in wind-pollinated plants and have been interpreted as outcrossing mechanisms, though few studies have investigated their function. Carex, a large genus of anemophilous herbs, is predominantly monoecious and many species are protogynous. We investigated whether monoecy and protogyny limit self-pollination in seven Carex species.
  • • 
    We conducted field experiments comparing stigmatic pollen loads and seed set between intact and emasculated stems. We tested for self-compatibility and evaluated pollen limitation of seed set by supplemental pollination. Finally, we measured outcrossing rates in open-pollinated and emasculated stems using allozyme markers.
  • • 
    Emasculated stems captured significantly less pollen than open-pollinated stems and set less seed. Pollen deposition during the female-only phase for intact stems was only 12% of the total captured. Outcrossing rates for three species indicated high selfing (range t = 0.03–0.39). Allozyme loci in the remaining species were monomorphic also suggesting high selfing. These results demonstrate that neither monoecy nor protogyny is particularly effective at limiting self-fertilization.
  • • 
    Selection for the avoidance of selfing is unlikely to maintain monoecy in many Carex species although protogyny may provide limited opportunities for outcrossing. We propose that geitonogamy in self-compatible wind-pollinated species with unisexual flowers may be widespread and provides reproductive assurance.