Dioicy

Dioicy, commonly referred to as dioecy in plants, is a sexual system in which individuals are exclusively male or female, bearing only one type of gamete. In flowering plants and many other lineages, dioecy means that male and female flowers occur on separate plants, preventing self-fertilization and typically promoting outcrossing. In bryophytes and some algae, the related term dioicous (or dioicy) is used to describe separate male and female gametophytes or individuals, with the sporophyte often dependent on the female gametophyte for nutrition.

In dioecious species, reproduction requires the interaction of distinct male and female sexes, often facilitated by pollinators or wind in plants, or water and physical contact in bryophytes. The genetic basis of dioecy can involve sex chromosomes or specific sex-determining genes, though environmental factors can also influence sex expression in some taxa. Dioecy can impose higher spatial requirements for cross-pollination or fertilization and may lead to skewed sex ratios under certain ecological conditions.

Distribution and examples vary by group. Many gymnosperms (such as Ginkgo biloba and date palm, Phoenix dactylifera) and several angiosperm lineages include dioecious species, as do numerous Populus (poplars) and Cannabis plants. Among bryophytes, dioecy is relatively common, with separate male and female gametophytes producing antheridia and archegonia, respectively.

Evolutionary considerations suggest dioecy can reduce inbreeding and promote genetic diversity, but it also requires mechanisms to bring male and female individuals into contact. In agriculture and horticulture, dioecious crops require management of both sexes to ensure seed production or fruiting. See also monoecy, hermaphroditism, and sex determination.