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Pitchie Ritchie Gorge, SA

seedling

racemes

pods

Natural populations

Acacia pycnantha occurs across much of Victoria and southeastern South Australia, including Eyre Peninsula and Kangaroo Island, with some extension into southern inland New South Wales, and at Mt Jerrabomba in the Australia Capital Territory [1,2]. There is an putative natural occurrence near Broken Hill, in western New South Wales. It has become naturalised in many areas of southern Australia, particularly the southwest of Western Australia [2]. This species is usually a shrub or small tree to 5 m tall but sometimes taller, often with white, pruinose bark on branches near the crown. It grows on a range of sites, from rocky ridge tops to low undulating terrain, and on variety soils including calcareous sands, clays and shallow, stony loams [1,2].

Flowering and seeds

Flowering occurs mainly during August to October but can extend from July to November [1,2]. From flowering it takes about 5-6 months for seed pods to mature, which is mainly during November to January. There are about 35 viable seeds per gram [3]. Nicking or boiling the seeds in water for a minute at 100°C is required to induce germination. The seeds start to germinate in about 10 days if grown at 25°C [3].

Cultivation and uses

Acacia pycnantha is a fast growing, nitrogen fixing shrub or small tree, which can be grown on recharge sites and a wide range of shallow soils [2]. This species was proclaimed as Australia’s official National Floral Emblem in 1988. It has become naturalised in number of areas outside its natural distribution in Australia (e.g., the south west of Western Australia).

Key descriptors:
Climate parameters
Mean annual rainfall: 200-850 mm
Rainfall distribution pattern uniform or winter
Mean annual temperature: 8-20 °C
Mean max. temperature of the hottest month: 22-34 °C
Mean min. temperature of the coldest month: -2-9 °C
Frosts per year: frost free or more or less frost free or up to 20
Frost intensity: light to moderate (0 to -5°C)
Altitude: 5-1100 metres
Tolerance of climate extremes
Drought: known to be moderately drought tolerant
Fire: killed by damaging fire does not regenerate foliage
Frost: tolerates frosts in the 0° to -5°C range
Soil factors
Texture clay loam, duplex texture contrast soils, heavy clay (greater than 50% clay), light to medium clay (35-50% clay), loam, sandy loam, sandy clay loam or sand
Soil pH reaction: acidic (less than 6.5), neutral (6.5-7.5) or alkaline (greater than 7.5)
Soil depth: skeletal to shallow (less than 30 cm)
Drainage: well-drained
Salinity: slightly to moderately saline or non-saline
Tolerance of adverse soils
Extremes in pH: acidity
Extremes in texture: clayey or sand
Salinity: nil - sensitive to saline soils or slight (2-4 dS m-1)
Soil waterlogging tolerance: nil - sensitive to waterlogged soils
Biological traits under cultivation
Habit: evergreen shrub less than 2 m tall or shrub or small tree less than 5 m tall, can be multi-stemmed from or near ground level
Longevity: short-lived less than 15 years
Growth rate: fast
Coppicing ability: nil or negligible
Root system: shallow and spreading, fixes nitrogen via root symbiot
Erosion control potential: excellent for clayey sites or excellent for sandy sites
Wood density: mod. to high (greater than 600 kg/cubic metre)
Carbon sequestration potential: low-moderate
Uses
Potential farm use: good ornamental attributes
Specialty products: pollen has value for apiculture, high tannin content in bark, seeds are edible (used traditionally by Aborigines)
Traditional Aboriginal uses: gum or resin (eaten or for adhesives) or seeds/fruits eaten
Urban use: good as an ornamental or amenity plant
Wildlife value: a critical food source for at least one species
Wood products: high quality fuelwood
Potentially undesirable attributes
Fire sensitivity: killed by severe fires (seeder)
Growth habit: shallow roots may outcompete adjacent plants
Weediness: listed at least once as a declared weed species or high potential based on its biology

References

[1] Boland DJ, Brooker MIH, Chippendale GM, Hall N, Hyland BPM, Johnson RD, Kleinig DA, McDonald MW, Turner JD (2006) Forest Trees of Australia. CSIRO Publishing, Collingwood.

[2] Maslin, B.R. and McDonald, M.W. (2004) AcaciaSearch-evaluation of Acacia as a woody crop option for southern Australia. Rural Industries Research Development Corporation Publication No. 03/017, Canberra.

[3] Cunningham GM, Mulham WE, Milthorpe PL, Leigh JH (1992) Plants of Western New South Wales, Inkata Press, Port Melbourne, Victoria.

[4] Gunn BV (2001) Australian Tree Seed Centre Operations Manual. Internal Publication, CSIRO Australian Tree Seed Centre, ACT. [Online at http://www.ensisjv.com/Portals/0/atsc-opmanualcomplete.pdf  Accessed March 2008]

Internet links

Charles Sturt University's Virtual Herbarium: http://www.csu.edu.au/herbarium/acacpycn.html

eFloraSA Electronic Flora of South Australia: http://www.flora.sa.gov.au/cgi-bin/texhtml.cgi?form=speciesfacts&family=&genus=Acacia&species=pycnantha&iname=&submit=Search

PlantNET National Herbarium of New South Wales: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Acacia~mearnsii

Wikipedia: http://en.wikipedia.org/wiki/Acacia_pycnantha

World Wide Wattle: http://www.worldwidewattle.com/infogallery/utilisation/acaciasearch/pdf/pycnantha.pdf

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