Terminology and History
– Monoecious comes from the Greek words for one house.
– The term monoecy was first introduced in 1735 by Carl Linnaeus.
– Darwin noted that the flowers of monoecious species sometimes showed traces of the opposite sex function.
– Monoecious hemp was first reported in 1929.
Occurrence
– Monoecy is most common in temperate climates.
– 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 are monoecious, including most watermelon cultivars.
– It is prevalent in Euphorbiaceae.
– Dioecy is replaced by monoecy in the polyploid subspecies of Empetrum nigrum E. nigrum ssp. hermaphroditum and polyploid populations of Mercurialis annua.
Maize
– Maize is monoecious since both pistillate (female) and stamenate (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 ovules of the pistillate flowers, diploid cells called megaspore mother cells undergo meiosis to produce haploid megaspores.
– In the anthers of the stamenate flowers, diploid pollen 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 amaranths, 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 on floral sex ratios.
