ACACIA: CHARACTERISTICS, HABITAT, SPECIES, CARE, DISEASES - BIOLOGY - 2024

Acacia is a genus of trees and shrubs in the Fabaceae family. They are found throughout the world, especially in Australia, Africa, Southeast Asia and America.

Depending on the species, they can be trees that reach up to 25 m in height, which grow in very hot environments and develop in thickets in coastal areas or at an average height above sea level, generally between 0 and 1000 m.

Acacia tree. Source: pixabay.com

This genus is the oldest within the vascular plant genera. Worldwide, approximately 1,300 species of this family are known, of which at least 1,000 are endemic to Australia.

The name of acacias comes from the Greek word akis, which means "a thorn or a spike." They are plants closely related to the Egyptian civilization, being sacred trees in their mythology. In addition, the Egyptian vessels were made with acacia wood and both its flowers and its wood have a high value.

In other countries acacias are used as a good source of fuel, as well as for medicinal and industrial uses. In addition, acacias are of great ecological importance, as they are nitrogen-fixing species in nature.

Fruit (pod) of Acacia. Source: pixabay.com

characteristics

Habit

Acacias are thorny trees or shrubs, which reach 20-25 m in height and have a diameter of 1 m. They can be deciduous or evergreen. The tree has a strange shape, with branches that grow upwards. In addition, the branches are alternate, being able to be without thorns or thorny.

Leaves

For their part, the leaves of this plant genus are on the ends of their branches, having a bluish-green to silver-gray color. Its leaves are delicately divided, giving the appearance of bipinnate leaves similar to those of ferns. In turn, the leaves present a pulvínulo, being able to be stipulated or not, and they have petioles. The margin of the leaves is entire.

Some species have highly flattened phyllode-like leaves that serve the same purpose as leaves, and other species have cladodes that still serve the function of a leaf. The leaves produce a sweet substance in their basal glands that attracts ants, bees and butterflies.

Pink-flowered acacia. Source: pixabay.com

flowers

The inflorescences have actinomorphic, hermaphroditic or unisexual flowers, without hypanthus, generally yellow.

Like the leaves, the flowers are located at the ends of the branches. Together these flowers form a yellow ball-like bloom. The flower buds can be white or light yellow.

The sepals (4-5) are attached at the base. The petals are small (4-5) but are larger than the sepals. They are located behind the long stamens and positioned in globose or cylindrical clusters or glomeruli.

For its part, the androecium has numerous stamens that are free from each other. The stamens are very long, cylindrical in shape and pubescent; furthermore, the anthers are more or less basifix and ovoid in shape, which may or may not have glands.

Regarding the gynoecium, these plants have the ovary sitting or stipitate, being able to have pubescence or not. The style is more or less cylindrical and the stigma remains wet.

Although most species of acacia have yellow flowers, they can also be found with purple or red flowers.

Fruit

As flowering passes, pods are formed that contain the seeds. These seeds are more or less discoidal, and may or may not have a stanza. They generally show a persistent, fleshy and highly developed funiculus.

Acacia in bloom. Source: pixabay.com

Taxonomy

According to taxonomy, the genus Acacia is divided into five groups of species, which are: Acacia (species from Australia and tropical Asia), Acaciella and Mariosousa (species from America), and Vachellia and Senegalia. In turn, the Acacia genus is made up of approximately 1067 existing species.

Its taxonomic classification is as follows:

Kingdom: Plantae

Superphylum: Embryophyta

Phylum: Tracheophyta

Class: Magnoliopsida

Order: Fabales

Family: Fabaceae

Subfamily: Mimosoideae

Tribe: Acacieae

Genus: Acacia Mill. (1754)

Acacia silk. Source: pixabay.com

Habitat and distribution

Acacia is a genus of plants with a pantropical distribution. It can be found in practically every tropical region on the planet, especially Australia and Africa.

Also, this genus can inhabit Spain where they are very popular. It is a species that grows endemic, introduced and sometimes behaves as an invasive species, after a forest fire has occurred.

It grows in bushes and in rocky areas, although depending on the species, it prefers rock-free soils. It thrives in very hot environments and is not tolerant of soils that remain moist. It requires at least 6 hours of light a day.

Species

Some common Australian species are Acacia dealbat a (silver wattle), Acacia decurrens (bronze wattle), Acacia mearnsii (black wattle), Acacia melanoxylon (blackwood wattle), Acacia longifolia (coast wattle), Acacia baileyana (acacia de cootamundra), Acacia adunca (Wallangarra acacia), Acacia acinacea (gold dust acacia), among others.

Meanwhile, in Central America the species Acacia sphaerocephala, Acacia cornigera and Acacia collinsii can be found. Likewise, in Asia the species Acacia pennata and Acacia auriculiformis can be found. Some details of certain species are as follows:

Acacia bush. Source: pixabay.com

Acacia farnesiana

It is a species possibly originating from tropical America that has been introduced to other tropical and subtropical areas. It is known as aromo, carambuco, and sponjeira. It grows in bushes on stony and bare soils, between 0 and 200 meters above sea level.

It has flowers with a lot of smell, which are used in the perfume industry, therefore, this species is widely cultivated in France. The seeds are used in Africa as a black tincture and to relieve coughs; also, in some places it is used as a substitute for tamarind. It is also useful as a wood for posts and palisades.

Acacia cyclops

It is an acacia cultivated as a forest species, which has been domesticated in maritime calcareous rocks and in coastal dunes. It grows between 0 and 100 meters above sea level.

Acacia melanoxylon

This acacia is cultivated as a forest, ornamental and soil fixing species. It behaves like an invasive species after a forest fire has occurred. It grows between 0 and 800 meters above sea level. It is known as black wattle, Australian wattle, and black crop wattle.

Acacia dealbata

It is grown as an ornamental or in dunes. It is a domesticated species but it also behaves like an invasive. It grows up to 1000 meters above sea level. It is commonly known as French acacia, acacia, mimosa, alcacia, alcarcia, and blue leaf wattle.

Acacia leaves. Source: pixabay.com

Acacia pycnantha

It is a tree between 4 and 8 m tall, which is cultivated as an ornamental species and as a tannin-producing plant. It grows up to 200 meters above sea level.

Acacia verticillata

It is a bush of about 5 m. It is cultivated as an ornamental plant and is sometimes introduced. It grows between 100 and 400 meters above sea level. It is a plant native to Australia and Tasmania. In particular, in Australia two varieties are known: verticillata and ovoid.

Golden acacia. Source: pixabay.com

Applications

In general, these trees or shrubs are cultivated on practically every continent to use their wood, rubber, extract tannins or use their flowers for perfumes. They are also considered ornamental and forest species.

Acacias, both the color of their flowers and the usefulness of their products, make them used by humanity. In this case, thanks to that beautiful color, they can be used to increase the beauty of public gardens and parks, as well as the streets where they are planted for ornamentation.

For their part, the flowers and their striking colors beautify the environment, in addition to perfuming the air that surrounds them with their fragrance.

In a medical sense, its young leaves can be used in juice or mixed with some foods to treat diarrhea and stomach pain. In turn, the extract of the leaves is used to treat tuberculosis, while the seeds can be used to combat sore throats.

With respect to other products, it is known that a good quality gum is extracted from the Acacia arabica species, which is known as gum arabic. Furniture made from its wood is very popular in many homes.

In Australia, black acacia wood is highly valued due to its high quality, durability and polished appearance. In North America, some people gift bunches of flowers as a present to loved ones.

Likewise, acacias are taken into account in the Bible, as the Shittah tree is a seyal Acacia, which was used in the construction of the Ark of the Covenant. Consequently, the acacia branch is also used as a symbol of immortality.

Usefulness of some species

Regarding economic importance, the most used is Acacia senegal, for the production of gum arabic. Secondly, the species Acacia nilotica and Acacia farnesiana, for producing a similar but lower quality gum.

Regarding its use as a dye species, the most cultivated is Acacia catechu, which produces cato or catechume, a substance that is used to protect materials from decomposition.

Silhouette of an Acacia at a sunset in Africa

Care

Acacias can be propagated through seeds, grafts, and cuttings. These evergreen plants don't need a lot of care to maintain and can grow easily.

However, some care is necessary. For example, its sowing in very humid soils should be avoided, since acacias hate humidity in the substrate since their root system is very sensitive to excess water. On the contrary, acacias need a warm climate to survive; in contrast, they do not survive winter.

In terms of light conditions, these trees need direct sunlight for at least 6 leaves a day so that they can grow healthy and develop numerous branches and green foliage.

Regarding fertilization, nitrogen applications help to produce very beautiful blooms. While in relation to the substrate, it is preferable that it is free of rocks since its roots grow very fast.

Acacia. Source: pixabay.com

Diseases and pests

In general, acacias are plants quite resistant to both diseases and pests. However, there are reports of diseases that can damage some acacia plantations such as:

Gum

It is a disease caused by Phytophthora sp. that causes necrotic lesions in the wood or logs of these plants. It is observed by an abundant exudation with a rubbery appearance from the trunk.

Heart or root rot

Heart rot is a disease caused by basidiomycete fungi on the stumps of the branches that causes deformation of the phyllodes and the stem. It can be seen as a fibrous white appearance along the heart of its wood; it can only be seen when the tree is cut down. This disease can be treated through planned pruning

For its part, root rot is caused by Ganoderma philippii. The characteristic of this disease is that the leaves of the trees turn pale and decrease in size and quantity, while reducing their growth rate. On the other hand, the shoots wither and severely affected trees can fall due to the action of the wind.

Philodium rust

It is a disease associated with the fungus Atelocauda digitat a, which causes serious damage to young leaves and stems, both in greenhouses and in the field. In addition, it also affects its seeds.

Pests

The beetle Oncideres impluviata also causes great damage to some acacias. This insect feeds on the shoots or whores of the segments where the leaves and bark have tender tissue.

As adults, females cut their jaws on the bark of the main branch, producing galleries with their larval young.

Typical view of Africa where animals are observed under an Acacia. Source: pixabay.com

References

1. Iberian Flora. 2019. Acacia. Taken from: floraiberica.es
2. Mishra, PP 2013. Acacia. In: Encyclopedia of cultivated plants: from Acacia to Zinnia. Cumo, C (ed). ABC-CLIO. 1307 p. Taken from: books.google.co.ve
3. Catalog of Life: 2019 Annual Checklist. Acacia. Taken from: catalogueoflife.org
4. The Taxonomicon. (2004-2019). Genus Acacia Mill. (1754). Taken from: taxonomicon.taxonomy.nl
5. Sánchez, M. 2019. What are the characteristics of the acacia tree? Taken from. gardening.com
6. Toloza, RR, Correa, MA, Dummel, DM, Friedl, RA, Hennig, HH 2010. Presence of damage and diseases in Black Acacia Acacia mearnsii de Wild in the Province of Misiones, Argentina. 14th Forest and Environmental Technical Conference. Faculty of Forest Sciences-UNAM. Taken from: inta.gob.ar
7. Lee, SS 2019. Diseases and potential threats in Acacia mangium plantations in Malaysia. Taken from: fao.org