A weed is any plant that colonises and persists in an ecosystem in which it did not previously exist. They may affect the economy, the environment, human health and amenity. Many plants introduced into Australia in the last 200 years are now weeds.
Plants that are weeds have a number of common characteristics. They usually produce large numbers of seeds. They are often excellent at surviving and reproducing in disturbed environments. They can usually thrive in a variety of conditions.
A weed can be an exotic species or a native species. Weeds can inhabit all environments; our cities, deserts, waterways, alpine areas and oceans.
Weeds invade bushland, particularly where there has been some disturbance to the natural processes in that environment, and can out compete native plants.
Throughout Australia, weeds are spreading faster than they can be controlled and management of them is consuming an enormous amount of resources. Some weeds are of particular concern and have been listed for priority management in legislation.
Not all of Australia’s weeds have come from other countries. Australian native plants can also become weeds. This usually occurs when species move into new areas where they have a competitive advantage over indigenous plants. An example of a native plant establishing itself outside its natural range is the Cootamundra Wattle Acacia baileyana.
Useful links for weed identification
Weeds in Australia, home page
Weeds Australia, Weed ID page
Weeds of National Significance
Sydney Weeds Committee, What is this weed?