Certainly, plant species with male and female PLANTS are not good candidates for staple food crops, nor for the co-evolutionary process that produced humanity's staple crops. The mating season is too tricky! You might have plenty of females but no males around, and you'd starve.
More to the point, you need a rapid progression of generations to "naturally" breed a useful food crop from an edible jungle plant. It also helps to have an aggressive colonizing habit. All our staple crops are essentially weeds that grow easily in disturbed soil. You need a plant that is highly effective at producing seeds. Thus, crops bred from grasses.
But neither separate FLOWERS, nor sexes combined in the same FLOWER, pose these problems.