In dioecious plants, the unisexual male flower is staminate, i.e., bearing stamens only, while the female is pistillate or bearing pistils only. For the production of fruits and seeds fertilisation must take place, which is possible only in the presence of both male and female flowers. When the plant is dioecious, it will give rise to the following situations-
(i) If the plant bears only pistillate flowers, fertilisation can take place with the help of pollinators.
(ii) If the plant bears only staminate flowers, fertilisation can't take place because female gamete is non-motile which can't reach the male gamete in order to fuse with it. When the plant is monoecious, i.e., carrying both stamen and pistil together, it may lead to self-fertilisation and production of seed.