Muscadine flowers can be either male, female, or self-fertile (or perfect). In nature, vines are either female or male, and only the female vines set fruit. Before there were self-fertile flowers, vineyards were planted with the female fruiting cultivars, and male plants were interspersed to pollinate the female vines. Thus, production was reduced because the male vines produce no fruit.
Fortunately, a few vines that had self-fertile flowers were discovered, and through breeding, this trait was introduced into new cultivars with good berry quality. This meant that self-fertile vines could be used to pollinate the female cultivars, and berries could be harvested from the entire vineyard.
Currently, most vineyards consist of a mix of female and self-fertile vines. Usually, the female vines have a lower and more inconsistent yield than the self-fertile vines, but have a larger berry size. However, with self-fertile cultivars with large berry size being developed, the planting of female cultivars will likely decline in the future.
Male flowers have extended stamens and are missing the female pistil. Female flowers have shorter reflexed stamens with nonfunctional pollen. Perfect flowers have functional pistils along with extended stamens with functional pollen.
Female cultivars often have reduced yields. This is sometimes because the calyptera dries down and does not fall off the pistil. Notice how these are brown and still attached as compared to the female flower above showing a green healthy calyptera excising from the pistil. This prevents pollen from reaching the stigma and thus the flower isn't pollinated.