DIOECIOUS OR DIOECIOUS PLANTS: CHARACTERISTICS AND EXAMPLES OF SPECIES - BIOLOGY - 2025

The dioecious plants are those belonging to the group of angiosperms in which male flowers and female flowers are in "feet" or different individuals; which is why the only way these plants can reproduce is through cross pollination.

The term dioecious comes from a Greek word that literally means “two houses” and is often used to refer to those plant species that produce flowers and seeds whose sex is divided into different “houses”.

Schematic representation of a dioecious plant species (Source: nclm via Wikimedia Commons)

As an analogy to the term "dioecious" we could consider human beings. In a human population, whose members all belong to the Homo sapiens species, the female and male sexual organs are "located" on different "feet": in men there are the penis and testicles and in women there is the vagina (with the exceptions).

These plants differ from a large part of the angiosperms, since the most common is to find species in which the female and male gametophytes (ovocells and pollen grains, respectively) are not only found in the same "foot" (monoecious plants), but even in the same flower (plants with bisexual or hermaphroditic flowers).

Characteristics of dioecious plants

Dioecious plants can be dicotyledonous or monocotyledonous. Some authors estimate that these represent more or less from 3 to 6% of all angiosperms; however, others count 7% for monocotyledonous species and 14% for dicotyledonous species, which adds up to more than 6%.

Charles Darwin, in a publication he made in 1876, assured that dioecious plants have, in some way, a reproductive advantage over plants that present other types of distribution of their gametophytes, since they reproduce exclusively through cross-pollination., which ensures an increase in variability.

However, this group of plants has the disadvantage that at least half of the population (especially the “male” plants) do not produce seeds. This makes it more difficult for dioecious plants to spread than monoecious or hermaphroditic plants, for example, since a single individual cannot propagate its species when it colonizes a new environment.

This dispersive limitation is directly related to the fact that dioecious plants cannot "self pollinate" to produce fertile seeds. It also has to do with the importance of the "pollinator movement", which must necessarily be between flowers of different sexes.

Ambient

Dioicity has been related to the spatial distribution of plants, tropical environments and flora, oceanic islands and oligotrophic environments (with very low amounts of nutrients).

It has also been related to some ecological attributes such as the formation of wood, climbing habits, entomophilia (pollination mediated by insects) and the formation of fresh fruits that are dispersed by animals, although these are not unique characteristics of dioecious plants.

A study published by Matallana in 2005 affirms that the tropical coastal vegetation has an abundant concentration of dioecious plants. What this author considers is due to the specific characteristics of these environments, a proposition supported by publications by other authors such as Bawa, in 1980.

Other sexual systems in angiosperms

Hermaphroditic plants, monoecious plants and dioecious plants (Source: Nefronus via Wikimedia Commons)

It is important to emphasize that there are not only dioecious, monoecious and hermaphrodite plants, as a bibliographic review shows that gynoecious and androdioic species have been described.

Gynodioics and androdioics are characterized by the existence of plants with female flowers and plants with hermaphrodite flowers, and by the presence of plants with male flowers and plants with hermaphrodite flowers, respectively.

Furthermore, certain authors acknowledge the existence of "trioic" species, which are those in whose populations there are individuals with female flowers, individuals with male flowers and individuals with hermaphrodite flowers, also known as "perfect flowers".

Examples of dioecious species

There are several examples of species with dioecious characteristics and some of the most representative and important, anthropocentrically speaking, will be mentioned below.

Pistacia vera

Photograph of male pistachio flowers (Source: Krzysztof Ziarnek, Kenraiz via Wikimedia Commons)

The pistachio, native to western Asia and the Near East, is produced by a deciduous (deciduous) tree that can be up to 30 feet tall. These fruits are highly valued around the world and the trees are grown in temperate regions almost all over the world.

Since it is a dioecious plant, the male flowers are produced by one "foot" and the female ones by another, which considerably hinders the sowing strategies of these plants. Male flowers are red, while female flowers are white.

All species of the genus Pistacia are dioecious plants.

Delicious actinidia

Photograph of the fruits of Actinidia deliciosa (Source: via Wikimedia Commons)

Kiwi is another good example of "popular" fruits produced on dioecious plants. Plants belonging to the genus Actinidia are characterized by their climbing habits and because they are woody.

Also of Asian origin, the presence of a "female" plant and another "male" plant is essential for the production of this delicious fruit.

Pimenta dioica

Foliage photography of Pimenta dioica (Source: Photo by David J. Stang via Wikimedia Commons)

Also popularly known as “allspice”, due to the mixture of flavors and aromas that its leaves and fruits have, P. dioica is a species belonging to the Myrtaceae family, native to Mexico and Guatemala, although it is also thought to come from Cuba and Jamaica.

As its name indicates, it is a dioecious plant and is highly exploited from a culinary point of view for the preparation of Caribbean dishes and is one of the main ingredients in “BB-Q” sauces that are produced industrially.

Cannabis sativa

Photograph of a Cannabis sativa plant (Source: Gaurav Dhwaj Khadka via Wikimedia Commons)

Hemp, Indian hemp, hashish, kif or marijuana, is also a dioecious plant that belongs to the Cannabaceae family.

It comes from subtropical Asia, but it is cultivated in many parts of the world; Although this practice is prohibited, since sedative, intoxicating and hallucinogenic substances are extracted from the female flower buds that are used as drugs for indiscriminate use.

However, these plants have also been typically exploited to obtain textile fibers and paper, as well as for the production of analgesic ointments and other alternative medicines for patients of different types (with glaucoma, cancer, depression, epilepsy, children with problems of aggressiveness, among others).

References

1. Bawa, KS (1980). Evolution of dioecy in flowering plants. Annual review of ecology and systematics, 11 (1), 15-39.
2. Darling, CA (1909). Sex in dioecious plants. Bulletin of the Torrey Botanical Club, 36 (4), 177-199.
3. Irish, EE, & Nelson, T. (1989). Sex determination in monoecious and dioecious plants. The plant cell, 1 (8), 737.
4. Käfer, J., Marais, GA, & Pannell, JR (2017). On the rarity of dioecy in flowering plants. Molecular Ecology, 26 (5), 1225-1241.
5. Matallana, G., Wendt, T., Araujo, DS, & Scarano, FR (2005). High abundance of dioecious plants in a tropical coastal vegetation. American Journal of Botany, 92 (9), 1513-1519.
6. Nabors, MW (2004). Introduction to botany (No. 580 N117i). Pearson.
7. Ohya, I., Nanami, S., & Itoh, A. (2017). Dioecious plants are more precocious than cosexual plants: A comparative study of relative sizes at the onset of sexual reproduction in woody species. Ecology and evolution, 7 (15), 5660-5668.
8. Renner, SS, & Ricklefs, RE (1995). Dioecy and its correlates in the flowering plants. American journal of botany, 82 (5), 596-606.
9. Simpson, MG (2019). Plant systematics. Academic press.
10. Wasson, RJ (1999). Botanica: The Illustrated AZ Of Over 10,000 Garden Plants And How To Cultivate Them. Hong Kong: Gordon Chers Publication, 85.