The consequences of monoecy and protogyny for mating in wind‐pollinated Carex

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.