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Acacia

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Acacia is a large genus of shrubs and trees within the Mimosoideae subfamily. These plants belong to the Fabaceae family, which is commonly known as the pea family. While the genus originally included species from Africa and South America, it is now primarily used for plants found in Australasia. Many species also grow in New Guinea, Southeast Asia, and the Indian Ocean.

These plants are incredibly diverse and play vital roles in their environments. In Australia, acacia forests are the second most common forest type. They cover approximately 8% of the total forest area in the country.

Physically, acacia plants show a variety of leaf structures. Many species have bipinnate leaves, which means the leaves are divided into many small leaflets. In some mature plants, these leaves are reduced to structures called phyllodes. A phyllode is a flattened leaf stalk that functions like a leaf.

Acacia penninervis (5368395701)
Acacia penninervis (5368395701)

The flowers of the acacia are often quite striking. They grow in clusters called spikes or cylindrical heads. These clusters can appear singly, in pairs, or in groups called racemes. Each cluster contains many tiny golden-yellow or creamy-white flowers. Each individual flower has four or five sepals and petals, plus more than 10 stamens. The style, a thread-like part of the flower, is longer than the stamens. After flowering, the plant produces a fruit known as a pod. These pods can be flat or cylindrical and contain seeds with a fleshy aril at the end.

The history of naming the acacia has been complex for botanists. Philip Miller first validly named the genus in 1754 in his book, *The Gardeners Dictionary*. Later, in 1913, scientists Nathaniel Lord Britton and Addison Brown selected a specific African species as the lectotype. A lectotype is a single specimen chosen to represent the name of a group. For a long time, scientists believed the genus contained about 1,352 species. However, in 1986, a scientist named Leslie Pedley argued that the genus was not monophyletic. A monophyletic group is one that includes an ancestor and all its descendants. Pedley suggested splitting the genus into three separate groups: Acacia, Senegalia, and Racosperma.

This split caused a significant scientific debate between different regions. One group of over 900 species was mainly native to Australia and nearby islands. This group was not closely related to the smaller African group that held the original type species. Because of this, there was a disagreement over which group should keep the name Acacia. Australian botanists wanted to keep the name for their large group of plants. They proposed a new type species, *Acacia penninervis*, to allow the majority of species to remain under the Acacia name.

Acacia dealbata kz09
Acacia dealbata kz09

In 2005, a decision was made to conserve the name Acacia for the Australian component. This decision was upheld at the 2011 International Botanical Congress in Melbourne.

The fossil record shows that acacia-like plants have existed for millions of years. Fossil seed pods similar to acacia have been found in the Eocene of the Paris Basin. Other fossils, named *Leguminocarpon*, have been found in Hungary from the late Oligocene. In Switzerland, fossils of *Acacia parschlugiana* and *Acacia cyclosperma* have been identified from Tertiary deposits. The oldest fossil pollen for an acacia species in Australia dates back 25 million years to the late Oligocene.

Acacia retinodes MucBotGard
Acacia retinodes MucBotGard

Today, there are more than 1,080 accepted species of acacia recognized by Plants of the World Online as of January 2025.

Acacia species interact deeply with their local ecosystems. They serve as a common food source and host plant for various animals. For instance, the imperial hairstreak butterfly, *Jalmenus evagoras*, feeds on at least 25 different acacia species. Some reptiles, such as the native house gecko in Australia, feed on the plant's sap. Various insects, known as Hemiptera, also consume the sap.

Acacia dealbata kz09
Acacia dealbata kz09

Humans also find many uses for these plants. Aboriginal Australians have traditionally harvested seeds to grind into flour for cakes. These seeds are very nutritious, containing up to 25% more protein than many common cereals. They also use the timber for making tools, weapons, fuel, and musical instruments.

Beyond traditional uses, acacia has significant economic and environmental impacts. Many species are grown in large plantations for commercial purposes. For example, two million hectares of commercial plantations have been established worldwide. Species like *Acacia mangium* and *Acacia mearnsii* are used for wood products, firewood, and fodder. The bark of the black wattle is also used to produce tannins. Tannins are substances used in the tanning industry to make leather. However, some species can also be problematic. In South Africa, at least 16 introduced acacia species are considered invasive. This means they can spread out of control and disrupt the local environment.

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🖼️ Images & Media (4)
File:Acacia dealbata kz09.jpg
Acacia dealbata kz09.jpg
File:Acacia penninervis (5368395701).jpg
Acacia penninervis (5368395701).jpg
File:Acacia retinodes MucBotGard.jpg
Acacia retinodes MucBotGard.jpg
File:Wattle sign. Olive Pink Reserve, Alice Springs.jpg
Wattle sign. Olive Pink Reserve, Alice Springs.jpg
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