Dioicy () is a sexual system in non-vascular plants where Archegonium (female organs) and Antheridium (male organs) are produced on separate plants in the gametophyte phase.
Description
Dioicy promotes
outcrossing.
Sexual dimorphism is commonly found in dioicous species.
Dioicy is correlated with reduced
sporophyte production,
due to spatial separation of
male and
female colonies, scarcity or absence of males.
The term dioecy is inapplicable to Bryophyte because it refers to the sexuality of vascular plant sporophytes.
Etymology
The words
dioicous and
di(o)ecious are derived from οἶκος or οἰκία and δι- (di-), twice, double. (
(o)e is
Iotacism, 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" is used to describe diploid sexuality (
sporophytic sexuality), and thus is used to describe
tracheophytes (vascular plants) in which the
sporophyte is the dominant generation.
Occurrence
Sixty-eight percent of
Marchantiophyta species,
57% to 60%
of
moss species, and 40% of
hornwort 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
Monoicous 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.
Hornwort 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
