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Summary
Acacia mearnsii is a fast-growing leguminous large tree native to Australia growing naturally in brown sandy clay soils and black peaty soils along swampy flats and riverbanks. Over 1000 Acacia species occur in Australia and there are over 1350 species identified so far. Typically Acacia mearnsii reaches 10m tall but can grow to 20m in the right conditions. It has a rounded crown often branching low to the ground and rough brown bark. Dark green leaves are feathery. Flowers are pale yellow. Flowering time is from early spring to late summer. Globular flower heads occur in large, fragrant sprays. Fruits dark brown pods, finely hairy This species is the world's premier source of tannins and it is widely cultivated in warm temperate to tropical areas for its wood and tannins [303]. In areas where it has been introduced, it is often considered a weed, and is seen as threatening native habitats by competing with indigenous vegetation, replacing grass communities, reducing native biodiversity and increasing water loss from riparian zones.
Physical Characteristics
Acacia_mearnsii is an evergreen Tree growing to 10 m (32ft) by 8 m (26ft) at a fast rate.
See above for USDA hardiness. It is hardy to UK zone 9 and is frost tender. The flowers are pollinated by Bees, insects. The plant is self-fertile.
It can fix Nitrogen.
It is noted for attracting wildlife.
Suitable for: light (sandy) and medium (loamy) soils, prefers well-drained soil and can grow in nutritionally poor soil. Suitable pH: mildly acid and neutral soils and can grow in very acid soils.
It cannot grow in the shade. It prefers moist soil. The plant is not wind tolerant.
UK Hardiness Map
US Hardiness Map
Synonyms
Acacia molllissima Willd. Racosperma mearnsii (De Wild.) Pedley
Plant Habitats
Edible Uses
Edible portion: Gum, Seeds.
The gum is eaten and dissolved in water and used to make drinks.
References More on Edible Uses
Medicinal Uses
Plants For A Future can not take any responsibility for any adverse effects from the use of plants. Always seek advice from a professional before using a plant medicinally.
The bark is rich in tannins and so can be used in the many ways that astringents can be employed such as to treat diarrhoea and dysentery, to treat haemorrhoids, stop internal bleeding, bathe cuts and abrasions, as a mouthwash to tighten the teeth in the gums etc[413 ].
References More on Medicinal Uses
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Other Uses
Agroforestry Uses: It grows well at high elevations, even on slopes with shallow or poor acid soils that are unstable and will not support agricultural crops[ 303 ]. It can, therefore, be very effective in preventing soil erosion. Densely packed plantations have proved effective in preventing further erosion, even on hillsides of up to 50 degrees slope[ 303 ]. The tree has been planted as a shelterbelt, a firebelt and as a shade tree in plantations[ 303 ]. An efficient nitrogen-fixer and good source of green manure, it thus can restore and regenerate soils[ 303 ]. Other Uses Wattle bark is the most widely used tannin material in the world[ 303 ]. It contains 30 - 45% (dry basis) high-quality tannins[ 303 ]. A powdered bark extract is also used to prepare tannin formaldehyde adhesives for exterior grade plywood, particleboard and laminated timber[ 303 ]. Possibilities of using the bark in the production of biodegradable polyurethane foam are being tested[ 299 ]. The heartwood is pale brown with a pinkish tinge; it is not sharply demarcated from the sapwood. The texture is moderately fine and uniform; the grain commonly interlocked; lustre is medium; there is no distinctive odour or taste.The wood is moderately hard to hard, heavy, fairly tough and strong, not very durable. It dries rapidly, but with pronounced warp, particularly cupping; shakes tend to open and knots to split slightly. It is moderately easy to work and polishes well. It is used for house poles, mine props, tool handles, cabinet work, joinery, flooring, construction timber and matchwood[ 303 , 316 ]. The pulp productivity is about 320 kg/cubic metre[ 303 ]. Testing has shown that it yields a pulp with good strength characteristics and is suitable for wrapping paper and hardboard. It is also used for rayon[ 303 ]. Originally distributed as a source of tannin, black wattle is now recognized as a valuable fuel wood[ 303 ]. The wood is moderately dense with specific gravity about 0.75, splits easily and burns well with a calorific value of 3,500 - 4,600 kcal/kg. The charcoal is extensively used in Brazil and Kenya, and in Indonesia the tree is extensively used as a domestic fuel and for curing tobacco[ 303 ].
Special Uses
References More on Other Uses
Cultivation details
A plant of warm temperate to subtropical areas, it can also be grown at moderate to high elevations in the tropics. It is found at elevations from 300 - 2,440 metres in areas where the mean annual temperature is in the range 9 - 20c and the mean annual rainfall is 500 - 2,050 mm[303 ]. It prefers a moderate climate, exhibiting great intolerance to extreme heat or cold[303 ]. Its lower altitudinal range is decided by the fact that trees cannot stand high summer temperatures, and the upper altitudinal limit is based on the fact that the tree does not tolerate temperatures below 0c[303 ]. Winter frosts and cold winds during the early part of the rainy season affect growth and survival rate, but older trees can withstand mild frost[303 ]. Localities experiencing severe hailstorms and snowfall are unsuitable[303 ]. Flourishes in deep, well drained, light textured and moist soils[303 ]. It thrives in well-aerated, neutral to acid soils, loamy soils, soils derived from shale or slate and is highly intolerant of alkaline and calcareous soils[303 ]. Soils with lateritic pan close to the surface are most unsuitable[303 ]. Adequate soil moisture is a prerequisite for satisfactory growth[303 ]. Trees cannot withstand drought because of their superficial root system and high rate of transpiration[303 ]. In Hawaii, A. Mearnsii is a noxious weed and spreads prolifically at elevations between 600 - 1,200 metres in the 1,000 - 1,200 mm rainfall zones[303 ]. The plant is also showing signs of being invasive in other areas, helped particularly by its prolific seed production and the long viability of the seeds in the soil[413 ]. Trees begin to yield fertile seed from the age of 5 years, giving good annual crops[303 ]. The tree regenerates naturally from seed after burning in clear-felled plantations[303 ]. Seed may lie dormant in the soil for up to 6 years without loss of viability[303 ]. The trees have strong light requirements and respond to thinning in the early years. Growth rate is comparatively slow for the first 1 or 2 years. Thereafter, both height and diameter increments are rapid up to the age of 6 - 7 years, after which they fall off gradually[303 ]. The tree has low coppicing power[303 ]. Taproot development largely depends upon the depth of the soil, but the tree has the general tendency to develop a superficial lateral root system. Because of this, trees are liable to being uprooted by strong gales during the monsoon season[303 ]. This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[200 ].
References Carbon Farming Information and Carbon Sequestration Information
Temperature Converter
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Plant Propagation
Seed - requires pre-treatment. This can be carried out by abrading the hard seed coat to allow the ingress of water[303 ]. A more common method is to soak the seed in warm or hot water prior to sowing. There are various different variations, one common method is to pour a small amount of almost boiling water over the seeds - this cools quickly so does not kill the seed. The seeds are then left in warm water for 12 - 24 hours prior to sowing[K ]. A germination rate of 75% occurs in 7-15 days[303 ]. The sown seeds are covered with bracken fronds to protect the beds from excessive evaporation and runoff during watering. The bracken cover is removed after germination[303 ]. Seedlings are pricked out when they are 5 - 6 cm tall with 3 or 4 pairs of leaves, planted into polythene bags 13 x 8 cm, and watered daily until out-planting. It is essential to shift the seedlings frequently to prevent them from striking roots in the ground. The seedlings should be about 9 months old at the time of planting[303 ]. Seeds stored in airtight containers at room temperature maintain their viability for several years[303 ]. Vegetative propagation by rooted cuttings is difficult[303 ].
Other Names
If available other names are mentioned here
Acácia-negra (Portuguese), Australian Acacia, Australische Akazie (German), Swartwattel (Afrikaans), Uwatela (Zulu).
Native Range
AUSTRALASIA: Australia, Tasmania, New South Wales (southeast), South Australia (southeast), Victoria, Australian Capital Territory,
Weed Potential
Right plant wrong place. We are currently updating this section.
Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.
Can be a noxious weed in Hawaii. Also potentially invasive in California, USA, Kenya, New Zealand, Tanzania, Réunion, Zimbabwe, and South Africa.
Conservation Status
IUCN Red List of Threatened Plants Status : This taxon has not yet been assessed.
Growth: S = slow M = medium F = fast. Soil: L = light (sandy) M = medium H = heavy (clay). pH: A = acid N = neutral B = basic (alkaline). Shade: F = full shade S = semi-shade N = no shade. Moisture: D = dry M = Moist We = wet Wa = water.
Expert comment
Author
De Wild.
Botanical References
3
Links / References
For a list of references used on this page please go here
A special thanks to Ken Fern for some of the information used on this page.
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Subject : Acacia_mearnsii
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