dioecy

Dioecy is a plant reproductive strategy in which individual plants are strictly male or strictly female, bearing unisexual flowers. In dioecious species, a single plant does not produce both pollen and ovules, so female individuals develop pistillate flowers and fruits after fertilization, while male individuals produce staminate flowers that release pollen. This condition contrasts with monoecy, where a single plant bears both sexes, and with hermaphroditism, where most flowers contain both male and female organs. Dioecy promotes outcrossing because cross-pollination is required between separate plants, with pollen dispersed by wind or animals.

Dioecy is relatively uncommon among flowering plants, occurring in about 5 to 6 percent of species, but it is common in several families such as Salicaceae (willows and poplars) and in the genera Actinidia (kiwifruit) and Phoenix (date palm), among others. The system imposes trade-offs: female plants pay the cost of seed production, while male plants invest predominantly in pollen production, and successful reproduction often depends on the presence of compatible mates nearby. Environmental factors or pollinator availability can influence the relative success of the sexes in a population.

Genetically, sex determination in dioecious plants is varied. Some species possess genetic sex-determining mechanisms and sex chromosomes (for example, certain Silene and Rumex taxa). In other lineages, sex expression is more plastic and can be influenced by environmental cues such as temperature, photoperiod, or resource status. In many populations, sex ratios are roughly balanced but can vary with age, year, or habitat conditions.

Examples of dioecious plants include willows (Salix spp.), poplars (Populus spp.), kiwifruit (Actinidia deliciosa), ginkgo biloba, cannabis (Cannabis sativa), and date palm (Phoenix dactylifera). Studying dioecy sheds light on plant reproductive strategies and the evolution of sex in flowering plants.