dioecie

Dioecy is a biological condition in which individual organisms are strictly single-sex: males produce only pollen or sperm, and females produce only ovules or eggs. In plants, this means that male and female flowers are borne on separate individuals. In animals, the term is often described as gonochorism, with distinct male and female individuals in a population. Dioecy is contrasted with monoecy or hermaphroditism, where a single individual bears both male and female reproductive organs or flowers.

Occurrence and mechanisms: Dioecy occurs in both plants and animals but is relatively uncommon among flowering plants, estimated at about 6–7% of species. Sex determination can be genetic (for example, XY or ZW systems in some taxa) or influenced by environmental factors in other cases. In dioecious plants, males produce pollen and often have conspicuous flowers to attract pollinators, while females produce ovules and, after fertilization, fruits. Some species show variation in sex expression or occasional sex changes under environmental stress, though individuals remain clearly male or female.

Examples: Well-known dioecious plant genera include Ilex (holly), Salix (willow), Populus (poplar), and Asparagus. Cannabis sativa is commonly described as dioecious in cultivation, with separate male and female plants. Advantages of dioecy include promotion of outcrossing and greater genetic diversity, whereas drawbacks include the need for both sexes to coexist for reproduction and potential vulnerability to skewed sex ratios.

Evolution and significance: Dioecy has evolved repeatedly in different lineages and influences mating systems, population genetics, and conservation strategies. It is one of several sexual systems observed across living organisms.