MALVACEAE: CHARACTERISTICS, HABITAT, REPRESENTATIVE SPECIES - BIOLOGY - 2024

The mallow (Malvaceae) are a family of flowering plants. They are characterized by having alternate leaves, stipules, a calyx formed by 5 sepals supported by an epicalyx, and pubecent and stellate trichomes (hair-like structures).

This family of plants has a variety of life forms, ranging from herbaceous, shrubs, to trees. They have a wide worldwide distribution (cosmopolitan). However, they are more and better represented in the tropical and subtropical regions.

Mexican cotton Gossypium hirsutum (Malvaceae). Taken and edited from: James Steakley.

To date, almost 4 thousand species of Malvaceae plants have been described in at least 250 genera. Many of these species are of ornamental and textile importance.

characteristics

The Malvaceae are plants with herbaceous life forms, shrubs and trees (few species of the latter); trees can become very large. They are covered by stellate trichomes. The stem of these plants generally has mucous channels and cavities and some species tend to have spines covering their entire surface.

Its leaves are simple, stipulate, alternate, with forms that vary from whole to partially divided, with nerves that are born at the apex of the petiole and are separated radially (palmatinervadas).

The flowers are generally perfect, rarely unisexual, with a superior ovary, that is, with the petals and stamens inserted in the receptacle below the gynoecium. They can be solitary or also be grouped in defined or undefined axillary inflorescences, cymoses. Some species have large flowers of varied and very showy colors.

The calyx consists of 5 fused or free sepals, supported by an epicalyx that can sometimes be absent. The corolla, on the other hand, has 5 petals generally attached to the base of the androecium, sometimes rolled up and can even be imbricated.

The androecium has anthers of a single theak and usually with filaments attached to several bodies or they can be arranged individually. The gynoecium is divided into 3 or up to 40 carpels (some authors indicate that they may have many more carpels); ovaries with as many locules as carpels.

The fruits are capsular, that is, dry and dehiscent, which may or may not be separated into mericarps. They can present from a single to numerous seeds, kidney-shaped or subglobose, without endosperm and with a straight or curved embryo.

Taxonomy

Malvaceae were first described by the renowned French physician and botanist Antoine Laurent de Jussieu in 1789 in the work entitled The genera of plants arranged according to natural orders.

The plants of the Malvacea family from the morphological point of view are a monophyletic group, that is, they descend from a single ancestral lineage. But molecular studies have determined that at least three of the subfamilies that make up the group are paraphyletic (they do not include all descendants of the same ancestor).

By presenting paraphyletic groups, the family is taxonomically called Malvaceae sensu lato, that is, in a broad sense. Artificially, the family is composed of 9 subfamilies, which are under constant scientific and taxonomic debate.

Of the malvaceae, about 250 genera and 3,929 species have been described to date. The Malvoideae subfamily is the one with the highest number of taxa, with 78 genera and more than 1500 species.

Habitat and distribution

The Malvaceae are a group of plants with a wide worldwide distribution. The patterns that govern this distribution are so many that it is difficult to establish specific distribution characteristics.

That said, it is generally known that Malvaceae are distributed in all the continents of the planet, with the exception of Antarctica where they have not yet been reported. They are more and better distributed in tropical and subtropical environments, with South America being the geographic area where there is the greatest known diversity.

These plants inhabit desert, semi-arid, as well as temperate climates. They can be found in humid tropical forests, scrublands, open savannas, on the margins of forested areas and also in saline coastal environments. However, in polar areas, in the tundra and taiga they are scarce or non-existent.

Flower of the mallow Sida rhombifolia. Taken and edited from: Bob Peterson from North Palm Beach, Florida, Planet Earth!.

Reproductive mechanisms

The reproduction and dispersal mechanisms of malvaceae are considerably varied. Many species attract insects so that they take care of pollination (melitophils), others produce nectar to attract certain species of birds such as hummingbirds to disperse their pollen.

Some have the so-called chiropterophilia syndrome, which consists of some plants having generally flared flowers that open and produce nectar at night to attract bats that are in charge of the pollination process.

A peculiarity that hermaphrodite plants present is that to avoid self-fertilization they present sequential dicogamy or hermaphroditism (equivalent to the term protandria, used in zoology).

The dicogamy consists of the development of male and female flowers at the same time, which then go on to have female and male functions respectively, reversing their sexual functionality.

Representative species

Sida rhombifolia

It is a species that lives below 2000 meters above sea level, grows in the shape of a bush and is of tropical and subtropical distribution, very resistant and can live in different types of soils. In some countries it is a highly invasive species.

This species commonly called escubilla or mallow de broom has many uses. Due to its fibers, it is of relative textile importance, however due to the quality of its cellulose it is more used to make paper money.

In some rural locations it is used to treat high fevers, as an antidiarrheal and even to produce antivenom and anti-spider bite. The plant produces bioactives such as alkaloids, so in some countries such as Mexico they use it as a substitute for Cannavis sativa.

Gossypium hirsutum

Also known as cotton or Mexican cotton, it is perhaps the best known of the malvaceae. Its cultivation could have begun between 5 - 8 thousand years ago, in territory that today belongs to Mexico, however other data suggest that it could have been about 7 thousand years ago in what is now India, Pakistan, Bhutan, Nepal and Bangladesh.

This species is the most cultivated of cottons worldwide and its main use is textile, however it is also used for the production of edible oils, soaps, fertilizer, secondary food for livestock and is even used as a base for the manufacture of explosives.

Hibiscus mutabilis

This mallow is known as malva or rose of Cuba. It is a shrubby plant native to the southern United States of America. It has an ornamental use since its flowers are large and showy.

A relevant characteristic about its flowers is that they are pink to white and can change to an intense red color (depending on the variety). In the morning hours the flowers are white but during the day they turn pink or red.

Color changes in the flower of the Malvaceae Hibiscus mutabilis. Taken and edited from: Vinayaraj

References

1. M. Gual-Díaz, N. Diego-Pérez (2018). Diversity of the Grewioideae and Tilioideae (Malvaceae) subfamilies in Guerrero, Mexico. Acta botánica mexicana.
2. C. Bayer & K. Kubitzki (2003). Malvaceae. In: K. Kubitzki (ed.), The Families and Genera of Vascular Plants, vol. 5, Malvales, Capparales and nonbetalain Caryophyllales. pp. 225-311.
3. Cottons and Jamaicas (Malvaceae). Recovered from biodiversity.gob.mx.
4. JB Rondón (2009). The subfamily Malvoideae (Malvaceae sl) in the western Sucre state, Venezuela. UDO Agrícola Magazine.
5. SR Hinsley (2014). Malvaceae info. Recovered from malvaceae.info.
6. PA Fryxell (1992). A Revised Taxonomic Interpretation of Gossypium L. (Malvaceae). Rheedea.
7. Malvaceae. Recovered from biologia.edu.ar.
8. Malvaceae family. Recovered from arbolesornamentales.es.
9. Malvaceae. Recovered from bibdigital.rjb.csic.es.
10. Malvaceae. Recovered from en.wikipedia.org.