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Acacia
Acacia auriculiformis

Black Wattle


Introduced from Australia, the Acacia is a fast growing tree that grows well even on poor soil. It is now common in wastelands throughout Singapore.
This tree has no leaves except when it is a seedling. When the seedling first sprouts, it has twice pinnate leaves. Subsequent leaves have enlarged leaf stalks with a little bit of true leaves and by the fifth "leaflet", it's all leaf stalk and no leaf! What you see are flattened leaf stalks called phyllodes, which are green and function as leaves. These are an adaptation to hot climates and droughts.
seedling with real leaves
Photo from Wee YC
Mangrove and wetland wildlife at
Sungei Buloh Nature Park
Main features: Crooked trunk, reaches 20-30m tall.

Bark: Fissured, grey or brown.

Leaves: None except when seedling: twice pinnate compound.

Flowers: Clusters, yellow, small, fragrant. Blooms at certain months of the year.

Fruits: A pod with seeds.
flowers
seed pods
Status in Singapore: Common in wastelands.

World distribution: Native to the savannah of New Guinea, islands of the Torres Strait, and northern Australia, but has since been introduced to a wide range of countries from Africa to Southeast Asia and the Pacific islands.

Classification: Family Leguminoseae.
The tree flowers quickly, within 1-2 years. The tiny yellow flowers are fragrant. The pods are first straight or slightly curved but as they ripen, they turn from yellow to brown and curl up, then split open. The black seeds hang from short curled orange stalks when the pod splits open. Birds find these seeds highly attractive and eat them. Thus the plant is very quickly dispersed.

Uses for food: Aborigines of Australia have traditionally harvested the seeds of some acacia species as food. These are ground into flour and eaten as a paste or baked into a cake. The seeds can contain 25% more protein than common cereals like rice or wheat, and their hard seed coats mean acacia seeds also store well for long periods.

Other uses: Acacias were purposely introduced and planted in Southeast Asia and Oceania as a source of firewood and good quality charcoal (does not smoke), as well as timber for furniture and pulp for making paper (acacia produces high yields of pulp and produces strong paper). The tannin produced from the tree is of a good quality, but tends to redden with exposure to sunlight. The tree was also introduced as an ornamental shade tree, but in Singapore, it is no longer grown as a wayside tree due to the large amount of litter of "leaves", flowers and fruits that the tree produces. In India, the tree was cultivated to feed the lac insect, which produces a resinous secretion that is harvested to produce lacquer.

Acacia has the potential to protect poor soils from erosion and revive their mineral content. Acacia can grow on poor soils including clay, limestone and unstable sand dunes, even soil tainted with uranium wastes. It is also able to survive fire, dry spells and seasonally waterlogged soil. (In fact, the seeds germinate better when placed in hot ashes!). The tree also contains nitrogen fixing bacteria which can help rejuvenate these poor soils. The tree prevents soil erosion because of their extensive and dense roots and heavy leaf litter. But the seedlings don't grow well in the shade and in competition with weeds, so for deliberate planting, the seedlings have to raised elsewhere first.

Traditional medicinal uses: A decoction of the root is used to treat aches and pains and sore eyes; an infusion of the bark treated rheumatism (aborigines of Australia).

Role in the habitat: Acacias recover wastelands, returning nutrients to poor soils and providing shade for other plants to take hold. They do not produce a lot of pollen or nectar as food, but their plentiful seed supply is a valuable food source for animals (mainly birds and also small mammals), particularly in dry places. Various insects eat their leaves and wood, and sugar gliders and squirrels may eat their sap. The trees also provide shelter for animals; as well as epiphytic plants.


LINKS REFERENCES
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Nature's Niche
  • Wee Yeow Chin, "A Guide to the Wayside Trees of Singapore", Singapore Science Centre, 1989 (p. 137-139: description, habitat, photo).
  • E. J. H. Corner, "Wayside Trees of Malaya: Vol I", Malayan Nature Society, 4th ed., 1997 (p. 447-449: description, habit, distribution).
  • Science Club, River Valley High School, "A Guide to the Flora and Fauna of Schools in Singapore", Hillview Publications, 1991 (p. 6: description, habits, habitat, photo).
  • Anne Nathan and Wong Yit Chee, "A Guide to Fruits and Seeds", Singapore Science Centre, 1987 (p. 70: description, habitat, photo).
 
By Ria Tan, 2001