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Tuesday, May 03, 2005

The Ecology of Australian Acacia
(1.) The foliage of most Australian Acacia species is bipinnate in juveniles, but phyllodinous in adults. A phyllode, is made from thickened leaf midrib, and more resistant to water loss than normal leaf tissue.

(2.) In Africa and America all the flowers within an Acacia flower head open simultaneously over 1-3 days. In Australia, the flowers within Acacia flower heads often opened in a staggered fashion, over several days.

(3.) The long-lasting flower heads of Acacia melanoxylon change colour as they age. This change in the colour is thought to allow all the flower heads on a plant to attract pollinators from a distance, and then to guide pollinating insects to the flower heads bearing the most pollen once they are close enough to discriminate between different flower heads.

(4.) My PhD research found that hoverflies were more frequent and reliable flower visitors to Acacia flower heads than native bees. It is possible that hoverflies flies, and some beetles, are important pollinators to some Australian Acacia. Unfortunately, large scale land-clearance and pesticide use in Australia have resulted in many pollinators being lost. If the pollinators of more native plants are not discovered, and protected, it will be impossible to conserve threatened species or to revegetate Australia using native plants adapted to local conditions.

(5.) An Acacia pycnantha flower head bearing large numbers of seed pods. It is possible that introduced honey bees, which collect large amounts of pollen from single flower heads and plants, were responsible for the unusually large numbers of seeds being produced on this species. It remains to be discovered whether honey bees are affecting the quality of the Acacia seed bank, due to their collecting and moving pollen between plants in new ways.