Dioecious species are whose members can produce only one type of gamete; each individual organism belonging to a dioecious species is distinctly male or female (the word deriving from the Greek for "two households"). The majority of animal species[1] (for example, all mammals and most reptiles) are dioecious. In plant sexuality, there are also dioecious species.
The term dioecious is typically used only of plants and plant species. In a dioecious species, no individual 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.
In most dioecious species the male plant is of heterogametic sex XY and the female plant is of homogametic sex XX. Exceptions where the male plants are of homogametic sex are Potentilla fruticosa and species of Cotula. A few plant families are exclusively dioecious, such as the willow family, Salicaceae.
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