Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system comparable with gynomonoecy, andromonoecy and trimonoecy, and contrasted with dioecy where individual plants produce cones or flowers of only one sex and with bisexual or hermaphroditic plants in which male and female gametes are produced in the same flower. Monoecy often co-occurs with

anemophily Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are many plants in the order Poales, including grasses, sedges, and rushes. Other common anemophilous ...

, because it prevents self-pollination of individual flowers and reduces the probability of self-pollination between male and female flowers on the same plant. Monoecy in

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

has been of interest for evolutionary biologists since

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

Terminology

Monoecious comes from the Greek words for one house.

History

The term monoecy was first introduced in 1735 by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

. Darwin noted that the flowers of monoecious species sometimes showed traces of the opposite sex function, suggesting that they evolved via hermaphroditism. Monoecious

hemp Hemp, or industrial hemp, is a plant in the botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial and consumable use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest ...

was first reported in 1929.

Occurrence

Monoecy is most common in temperate climates and is often associated with inefficient pollinators or wind-pollinated plants. It may be beneficial to reducing pollen-stigma interference, thus increasing seed production. Around 10% of all seed plant species are monoecious. It is present in 7% of angiosperms. Most

Cucurbitaceae The Cucurbitaceae (), also called cucurbits or the gourd family, are a plant family (biology), family consisting of about 965 species in 101 genera.

are monoecious including most watermelon

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s. It is prevalent in

Euphorbiaceae Euphorbiaceae (), the spurge family, is a large family of flowering plants. In English, they are also commonly called euphorbias, which is also the name of Euphorbia, the type genus of the family. Most spurges, such as ''Euphorbia paralias'', ar ...

. . . Dioecy is replaced by monoecy in polyploid populations of '' Mercurialis annua''.

Maize

Maize is monoecious since both

pistil Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl (botany), whorl of a flower; it consists ...

late (female) and

stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

ate (male) flowers occur on the same plant. The pistillate flowers are present on the ears of corn and the stamenate flowers are in the tassel at the top of the stalk. In the

ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...

s of the pistillate flowers,

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

cells called megaspore mother cells undergo

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

to produce haploid megaspores. In the anthers of the stamenate flowers, diploid

pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

mother cells undergo meiosis to produce pollen grains. Meiosis in maize requires gene product RAD51, a protein employed in recombinational repair of DNA double-strand breaks.

Evolution

The evolution of monoecy has received little attention. Male and female flowers evolve from hermaphroditic flowers via andromonoecy or gynomonoecy. In

amaranth ''Amaranthus'' is a cosmopolitan distribution, cosmopolitan group of more than 50 species which make up the genus of annual plant, annual or short-lived perennial plants collectively known as amaranths. Some names include "prostrate pigweed" an ...

s monoecy may have evolved from hermaphroditism through various processes caused by male sterility genes and female fertility genes. Monoecy may be an intermediate state between hermaphroditism and dioecy. Evolution from dioecy to monoecy probably involves

disruptive selection In evolutionary biology, disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait in ...

on floral sex ratios. Monoecy is also considered to be a step in the evolutionary pathway from hermaphroditism towards dioecy. Some authors even argue monoecy and dioecy are related. But, there is also evidence that monoecy is a pathway from sequential hermaphroditism to dioecy.

References