Acacia facts for kids

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Acacia
Acacia greggii
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Fabales
Family: Fabaceae
Subfamily: Mimosoideae
Tribe: Acacieae
Genus: Acacia
Mill.
Species

About 1,300; see List of Acacia species

Acacia drepanolobium MHNT.BOT.2011.3.97
Acacia drepanolobium
Acacia sp. MHNT.BOT.2009.13.18
Acacia sp.

Acacia is a genus of shrub or tree are belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian Acacias are not.

Defences

Whistling thorn
The Whistling Thorn (Acacia drepanolobium).
This species of acacia grows two kinds of thorns. The main defense is provided by pairs 5cm long arranged nearly at a right angle. Smaller stipular spines grow between the pairs of big thorns. These emerge from hollow galls, bulbous swellings 2 to 3cm across. One of four different species of ant lives in each of these igloos, which they open up by cutting holes into them. A dying bush whistles as the wind blows over these entrances.
Most acacias make toxins that it rushes to leaves that are under attack by browsers. The whistling thorn does not. It is infested with stinging ants that swarm out and prepare to bite anything they can when the branch is disturbed. Most browsers seem to avoid infested bushes, perhaps because the ants stink of formic acid.

Acacias are heavily defended against herbivores. Different species have different combinations of defences:

  1. Thorns
  2. Chemicals: bitter tannins and psychoactive alkaloids are common in Acacias. Some species have up to 40% tannins in their bark
  3. Ants: in Africa and Central Americs, symbiosis with ants can deter all sizes of enemy, from elephants to caterpillars and stem-boring beetles. Some species of ants will also fight off competing plants around the acacia, cutting off the offending plant's leaves with their jaws and ultimately killing it. Other associated ant species appear to do nothing to benefit their hosts.

Products from the Acacia have often been used for medicinal purposes.

Fossil record

An Acacia-like 14 cm long fossil seed pod has been described from the Eocene of the Paris Basin. Acacia like fossil pods under the name Leguminocarpon are known from late Oligocene deposits at different sites in Hungary. Seed pod fossils of †Acacia parschlugiana and †Acacia cyclosperma are known from Tertiary deposits in Switzerland,. †Acacia colchica has been described from the Miocene of West Georgia. Pliocene fossil pollen of an Acacia sp. has been described from West Georgia and Abkhazia. Oldest records of fossil Acacia pollen in Australia are from the late Oligocene epoch, 25 million years ago.

Distribution and habitat

Acacia facsiculifera seedling
Acacia facsiculifera shoot

They are present in all terrestrial habitats, including alpine settings, rainforests, woodlands, grasslands, coastal dunes and deserts. In drier woodlands or forest they are an important component of the understory. Elsewhere they may be dominant, as in the Brigalow Belt, Myall woodlands and the eremaean Mulga woodlands.

In Australia, Acacia forest is the second most common forest type after Eucalypt forest, covering 980,000 square kilometres (378,380 sq mi) or 8% of total forest area. Acacia is also the nation’s largest genus of flowering plants with almost 1,000 species found.

Description

Several of its species bear vertically oriented phyllodes, which are green, broadened leaf petioles that function like leaf blades, an adaptation to hot climates and droughts. Some phyllodinous species have a colourful aril on the seed. A few species have cladodes rather than leaves.

Uses

Aboriginal Australians have traditionally harvested the seeds of some species, to be ground into flour and eaten as a paste or baked into a cake. The seeds contain as much as 25% more protein than common cereals, and they store well for long periods due to the hard seed coats. In addition to utilizing the edible seed and gum, the people employed the timber for implements, weapons, fuel and musical instruments.

In ancient Egypt, an ointment made from the ground leaves of the plant was used to treat hemorrhoids.

A number of species, most notably A. mangium (hickory wattle), A. mearnsii (black wattle) and A. saligna (coojong), are economically important and are widely planted globally for wood products, tannin, firewood and fodder. A. melanoxylon (blackwood) and A. aneura (mulga) supply some of the most attractive timbers in the genus. Black wattle bark supported the tanning industries of several countries, and may supply tannins for production of waterproof adhesives.

Acacia is repeatedly mentioned in the Book of Exodus, perhaps referring to Acacia raddiana, in regards to the construction of the Tabernacle.

Acacia is a common food source and host plant for butterflies of the genus Jalmenus. The imperial hairstreak, Jalmenus evagoras, feeds on at least 25 acacia species.


Acacia Facts for Kids. Kiddle Encyclopedia.