flowering plants having both bisexual and unisexual flowers. A plant may have both bisexual and male flowers (andromonoecism; for example, in hellebore) or bisexual and female flowers (gynomonoecism; for example, in catchfly and many plants of the family Compositae). Some plants may have bisexual flowers, male flowers, and female flowers (trimonoecism; for example, in horse chestnut). Some specimens of a polygamous species have bisexual flowers, and others have male flowers (Dryas) or female flowers (forget-me-nots and many plants of the family Labiatae). In some species the bisexual, male, and female flowers may be on different plants (trioecism; ash and grape). There are variations within the above types. Polygamy in plants promotes cross-pollination.