Mulga

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In botany, a Mulga (Acacia aneura) is a shrub or small tree native to arid outback Australia. More broadly, mulga is any of many similar species, or more broadly still, a landscape where the flora is dominated either by Mulga or by similar species. This third usage is probably the most common of the three.

Mulga-dominated scrub, and hummock grasslands wooded with mulga cover roughly 20% of the Australian continent, or about 1.5 million square kilometres. Although Australia is best known for Eucalyptus trees, Mulga is easily the most common tree species of all. Mulga scrub is distinctive and widespread.

Mulga has developed extensive adaptations to the Australian desert. Like many acacias, Mulga has thick-skinned phyllodes. These are optimised for low water loss, with a high oil content, sunken stomata, and a profusion of tiny hairs to reduce transpiration. During dry periods, a Mulga drops much of its foliage to the ground, which provides an extra layer of mulch and from where the nutrients can be recycled.

The needle-like phyllodes stand erect to avoid as much of the midday sun as possible and capture the cooler morning and evening light. Any rain that falls is channeled down the phyllodes and branches to be collected in the soil immediately next to the trunk, providing the tree with a more than threefold increase in effective rainfall. Mulga roots penetrate far into the soil to find deep moisture. The roots also harbour bacteria that fix atmospheric nitrogen and thus help deal with the very old, nutrient poor soils the species grows in.

Several similar species are also known as mulga. These include:

Umbrella Mulga, Acacia brachystacya
Bendee, Acacia catenulata
Black Mulga, Acacia citrinoviridis
Hop Mulga, Acacia craspedocarpa
Bowgada, Acacia linophylla
Horse Mulga, Acacia ramulosa

True Mulga is highly variable, in form, in height, and in shape of phyllodes and seed pods. It can form dense forest up to 15 metres high, or small, almost heath-like low shrubs spread well apart. Most commonly, it is a tall shrub. Because it is so variable, the taxonomy of the Mulga has been studied extensively, and although it is likely to be split into several species eventually, there is as yet no consensus on how or even if this should be done. Although generally small in size, Mulga is long-lived, a typical lifespan for a tree undisturbed by fire is in the order of 200 to 300 years.

There are a number of recognised varieties:

A. aneura var. aneura
A. aneura var. argentea
A. aneura var. fuliginea
A. aneura var. intermedia
A. aneura var. macrocarpa
A. aneura var. major
A. aneura var. microcarpa
A. aneura var. pilbarana
A. aneura var. tenuis

Mulga is of great economic important to Australia, especially the pastoral industry, as it is palatable to stock and provides up to 12% crude protein. It is also an historically important source of timber for fencing and buildings.

References

Wikispecies has information related to:

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[Flora of Australia Online] s.v. [Acacia aneura].
[Flora of Western Australia] s.v. [Acacia aneura].

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