Dioecy (Greek: "two households"; adjective form: dioecious) is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male. The majority of animal species[1] (for example, all mammals and most reptiles) are dioecious. The term is rarely used for animals, probably because it is the common state for animals. The term is most often used in plants. The majority of plant species are monoecious, and hence have either bisexual flowers or possesses both male and female flowers on the same plant; but still a significant number of plant species are dioecious. See plant sexuality,[2][3] for a full description of more complicated situations in plants.
The term dioecious is typically used only in plants and plant species. Among flowering plants, dioecy is rare with about 6% of angiosperm species being dioecious.[4] Dioecious refers to a plant population having separate male and female plants. No individual plant can produce both microspores and megaspores; individuals of the species are either androecious (male, producing microspores) or gynoecious (female, producing megaspores). Dioecious species cannot self-fertilize.
Individual plants are either male or female.[5] From Greek for "two households". [Individual plants are not called dioecious; they are either gynoecious (female plants) or androecious (male plants).] In most dioecious species the female plant is of homogametic sex XX and the male plant is of heterogametic sex XY. Exceptions where the male plants are of homogametic sex are Potentilla fruticosa and species of Cotula. Some plant genera are exclusively dioecious, such as willows and poplars.