Dioicy () is a

sexual system A sexual system is a pattern of sex allocation or a distribution of male and female function across organisms in a species. Terms like reproductive system and mating system have also been used as synonyms. The distinction between sexual systems ...

where archegonia and

antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...

are produced on separate

gametophytes A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sex ...

. It is one of the two main sexual systems in bryophytes. Both dioicous () and

monoicous Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...

gametophytes produce gametes in gametangia by mitosis rather than

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...

, so that sperm and eggs are genetically identical with their parent gametophyte.

Description

Dioicy promotes

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a usefu ...

Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

is commonly found in dioicous species. However, according to Bernard Goffinet sexual dimorphism is rare in dioicous moss species. Dioicy is correlated with reduced sporophyte production, due to spatial separation of

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

and

female Female ( symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction. A female has larger gametes than a male. Females ...

colonies, scarcity or absence of males. The term dioecy is meaningless for bryophytes because it refers to the sexuality of sporophytes. Nonetheless dioecy and dioicy are comparable in many respects.

Etymology

The words dioicous and di(o)ecious are derived from οἶκος or οἰκία and δι- (di-), twice, double. (''(o)e'' is the Latin way of transliterating Greek οι, whereas ''oi'' is a more straightforward modern way.) Generally, the term and "dioicous" have been restricted to description of haploid sexuality ( gametophytic sexuality), and are thus primarily to describe bryophytes in which the gametophyte is the dominant generation. Meanwhile, "dioecious" are used to describe diploid sexuality ( sporophytic sexuality), and thus are used to describe

tracheophytes Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

(vascular plants) in which the sporophyte is the dominant generation.

Occurrence

68% of

liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...

species, 57% to 60% of moss species, and 40% of hornwort species are dioicous. Dioicy also occurs in algae such as

Charales Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus '' Nitellopsis'', living (extant) species are placed into either one family (Ch ...

and

Coleochaetales Coleochaetaceae is a family of algae. It is the only family in the Coleochaetales, an order of parenchymous charophyte algae, that includes some of the closest multicellular relatives of land plants. They questionably include the fossil genus ...

.It is also prevalent in

brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...

. In all cases sex determination is genetic.

Evolution of dioicy

The ancestral

in bryophytes is unknown but it has been suggested

monoicy Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...

and dioicy evolved several times. It has also been suggested that dioicy is a plesiomorphic character for bryophytes. In order for dioicy to evolve from monoicy it needs two mutations, a male sterility mutation and a female sterility mutation.

Hornworts Hornworts are a group of non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, hornworts have a g ...

have gone through twice as many transitions from dioicy to monoicy than monoicy to dioicy. Among moss species the transition from monoicy to dioicy is more common than dioicy to monoicy with there being at least 133 transitions from monoicy to dioicy in moss. Sexual specialization has been used as an explanation for this recurring evolution of dioicy in mosses.

References

{{reflist Bryophytes Plant sexuality Sexual system