androdioecious [ an-droh-dahy-EE-shuhs ] adjective: having male reproductive organs on one plant and bisexual (perfect) flowers on another plant of the same species
dioecious [ dahy-EE-shuhs ] adjective: plant species having male and female reproductive organs on different individual plants
gynodioecious [ gahy-noh-dahy-EE-shuhs ] adjective: having female reproductive organs on one plant and bisexual (perfect) flowers on another plant of the same species
monoecious [ muh–NEE-shuhs ] adjective: plant species having male and female reproductive organs on the same plant
polygamodioecious [ puh–LIG–uh-mo-dahy-EE-shuhs ] adjective: plant species having male and female reproductive organs on different individual plants along with bisexual (perfect) flowers on each plant; polygamous
In the broadest sense, the majority of plants are monoecious. In the strictest definition of monoecious, an individual plant hosts two kinds of flowers: male (or staminate), bearing only functional stamens, and female (or pistillate), having only functional pistils. Usually plants that reproduce via “perfect” flowers, meaning they are complete in themselves, having both male and female organs within the same structure, are called bisexual (also, cosexual or hermaphroditic). However, some consider plants with perfect flowers monoecious as well, since they possess male and female reproductive parts on the same plant.
According to forester Kim Coder at the University of Georgia, in the Eastern United States, 40% of trees (including beech, birch, hazel, hemlock, hickory, most pine, sweetgum, walnut, and white cedar) are monoecious (having male and female flowers on the same plant), while world wide, a mere 10% of trees are monoecious. When we consider the percentage of trees that are bisexual, we find that worldwide, the figure is 75%, while in the Eastern United States, it is only 30%. Those Eastern US species having perfect flowers include apple, cherry, dogwood, magnolia, redbud, rhododendron, and tuliptree. The remainder mainly fall into two categories, the dioecious and the polygamodioecious (also polygamous). Some species may change gender as they mature and some individuals may even change gender from season to season (Coder 2021).
Male and female flowers of monoecious plants left to right:
Betula nigra, Corylus avellana ‘Contorta,’ Liquidambar styraciflua, Pinus taeda, Tsuga canadensis.
Perfect flowers left to right: Cercis canadensis cultivar, Cornus florida, Magnolia virginiana, Malus coronaria, Rhododendron periclymenoides.
So why should we care about the sex of our plants? It matters whether or not we want our plants to produce fruit. In monoecious plants, you only need one plant of a species to produce fruit. Dioecious species, on the other hand, have separate male and female plants. Most of us as gardeners know that holly plants come in male and female varieties. You need at least one ‘Jim Dandy’ to pollinate your cluster of ‘Betty Jo’ or ‘Red Sprite’ Ilex verticillata (winterberry), and a ‘Jersey Knight’ or other male variety of Ilex opaca (American holly) to fertilize your ‘Jersey Princess’ or other lady hollies if you want them to bear fruit in the fall. One male plant can pollinate numerous female plants–how many depends on how closely they are planted to each other.
Dioecious plants left to right: Ilex verticillata ‘Red Sprite’ (flowers, with male ‘Jim Dandy,’ and with Northern Mockingbird),
Ilex verticillata ‘Winter Red,’ Ilex verticillata ”Sparkleberry,’ Ilex verticillata ‘Winter Gold’ (in October and in February).
Dioecious plants depend on fertilization via insects, bats, or birds, or even human hand pollination in some crops. Other dioecious plants you may know include aspen, currant, date, Gingko biloba (maidenhair tree), kiwi, persimmon, pistachios, redcedar, white ash, willow, and many junipers. The gingko, a tree with a nearly 200-million-year history, provides an example of why one might want to plant only male trees, as some cities do on public streets. The fruits of the female trees, while attractive, become a malodorous nuisance when they eventually fall to the ground and begin to decompose.
Polygamodioecious plants have bisexual (perfect) flowers along with either male flowers or female flowers on the same plant. Since the male or female flowers usually dominate a single plant with just a sprinkling of bisexual flowers, they may be described as “mostly male” or “mostly female.” This explains why in the same season and under the same conditions, you may observe one tree laden with fruit and a neighboring tree of the same species with a sparse yield. In the Eastern U.S. (and worldwide) about 10% of trees (including black gum, locust, red maple, and sumac) are polygamous.
A gynodioecious species has bisexual (perfect or hermaphrodite) flowers on one plant and female flowers on another plant. Although the female flowers have smaller perianths and produce less nectar and little to no viable pollen, they yield more or higher quality seeds than the bisexual flowers. However, in a habitat dominated by female plants of a species, reproduction is likely to be less successful. The prevalence of gynodioecy in angiosperms is not known, although it considered to be small. Some believe that gynodioecy is a route to dioecy. Some native examples of gynodioecious species are Fragaria virginiana (wild strawberry), Geranium maculatum (wild geranium), and Lobelia siphilitica (great blue lobelia).
Gynodioecious plants left to right: Fragaria virginiana, Geranium maculatum, Lobelia siphilitica.
An androdioecious species has bisexual flowers on one plant and male flowers on another plant. Its occurrence is very rare and has only been confirmed on a few taxa, including Datisca glomerata (Durango root), a wind-pollinated angiosperm native to California and Nevada. “The rarity of androdioecy relative to gynodioecy indicates that conditions for the invasion of a female-sterile form are more difficult to meet than conditions for the invasion of a male-sterile form” (Gleiser & Verdú 2004).
Note: Click on images to see enlarged photos, captions, and photo attributions.
On a mobile phone, click on the information symbol (circle with a letter ℹ︎ symbol).
References
Botanical Terminology: Flowers, Houses and Sexual Reproduction. Horticulture and Home Pest News. Iowa State University Extension and Outreach. [sccessed October 20, 2022).
Coder KD. 2021. Are your trees boys or girls — or both? CAES Newswire. College of Agricultural & Environmental Sciences. UGA Cooperative Extension.
Elmore W. 2017. Monoecious vs Dioecious: Self-Pollinating vs Cross-Pollinating Plants. Blogs. University of Florida.
Gleiser G, Verdú M. 12 November 2004. Repeated evolution of dioecy from androdioecy in Acer. New Phytologist. 165(2): 633–640.
Molano-Flores B. 2004. Breeding systems of Plants Used for Prairie Restorations: A Review. Transactions of the Illinois State Academy of Science. 97(2): 95–102.
Nyssa sylvatica. North Carolina Extension Gardener Plant Toolbox. North Carolina Cooperative Extension.
Wolf D, Rieseberg LH, Spencer SC. 1996. The genetic mechanism of sex determination in the androdioecious flowering plant, Datisca glomerata (Datiscaceae). Heredity. 78(197): 190—204.