The cucumber is a fruiting body, see the seeds, so must come from a female flower, but I learned this from Chuck in an earlier discussion. I quote him ...
"There are three TYPES of cucumbers. Gynoecious, Parthenocarpic and Monocious. The Gynoecious type has only female flowers, the flowers with the little tiny cucumbers. The Parthenocarpic type cucumbers can have both sexes of flowers, require no pollination and are the type used mainly in greenhouses where there are no pollinators. The Monocious type cucumber has both male and female flowers and it requires pollinators. Having said all this, how you tell a female flower from a male flower, is that the female flower has a little tiny cucumber growing from the base of the flower and on male flowers there isn't anything, it is just attached to the stem."