Dioicy () is a sexual system where

archegonia An archegonium (pl: archegonia), from the ancient Greek ''ἀρχή'' ("beginning") and ''γόνος'' ("offspring"), is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female ga ...

and antheridia are produced on separate gametophytes. It is one of the two main sexual systems in

bryophytes The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited i ...

. Both dioicous () and monoicous gametophytes produce gametes in gametangia by

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

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

Description

Dioicy promotes outcrossing. Sexual dimorphism 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 A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...

production, due to spatial separation of male and female colonies, scarcity or absence of males. The term

dioecy Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

is meaningless for

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 A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

sexuality), and are thus primarily to describe

in which the gametophyte is the dominant generation. Meanwhile, "dioecious" are used to describe diploid sexuality (

sporophytic A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...

sexuality), and thus are used to describe tracheophytes (vascular plants) in which the

is the dominant generation.

Occurrence

68% of liverwort species, 57% to 60% of

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...

species, and 40% of

hornwort 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 ...

species are dioicous. Dioicy also occurs in algae such as Charales and Coleochaetales.It is also prevalent in brown algae. In all cases sex determination is genetic.

Evolution of dioicy

The ancestral sexual system in bryophytes is unknown but it has been suggested monoicy and dioicy evolved several times. It has also been suggested that dioicy is a

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...

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 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 Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...

has been used as an explanation for this recurring evolution of dioicy in

mosses Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and horn ...

References

{{reflist Bryophytes Plant sexuality Sexual system