Sexual system

A sexual system is a distribution of male and female function across organisms in a species. The terms reproductive system and mating system have also been used as synonyms.

Sexual systems are a key factor for genetic variation and reproductive success, and may also have led to the origin or extinction of certain species. The distinctions between different sexual systems is not always clear due to phenotypic plasticity.

Interests in sexual systems go back to Darwin, who found that barnacles contain species that are androdioecious and some that are dioecious.

Types of sexual systems
Flowering plants may have dimorphic or monomorphic sexual systems. In monomorphic sexual systems, a combination of hermaphrodite, male, and/or female flowers may be present on the same plant. Monomorphic sexual systems include monoecy, gynomonoecy, andromonoecy, and trimonoecy. In dimorphic sexual systems, individual plants within a species only produce one sort of flower, either hermaphrodite or male, or female. Dimorphic sexual systems include dioecy, gynodioecy, androdioecy, and trioecy.

Male (a.k.a. staminate) flowers have a stamen but no pistil and produce only male gametes. Female (a.k.a. pistillate) flowers only have a pistil. Hermaphrodite (a.k.a. perfect, or bisexual) flowers have both a stamen and pistil. The sex of a single flower may differ from the sex of the whole organism: for example, a plant may have both staminate and pistillate flowers, making the plant as a whole a hermaphrodite. Hence although all monomorphic plants are hermaphrodites, different combinations of flower types (staminate, pistillate, or perfect) produces distinct monomorphic sexual systems.

In animals, androdioecy, gynodioecy, and trioecy are referred to as mixed sexual systems; where hermaphrodites coexist with single sexed individuals.