Weeds are often grouped in categories depending on their characteristics and impacts. Many weeds occur in more than one category. For example, alligator is a water weed and is also listed as one of Australia's Weeds of National Significance.
In NSW all plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
Under the National Weeds Strategy, 32 introduced plants have been identified as Weeds of National Significance (WONS). A list of 20 was endorsed in 1999 and a further 12 were added in 2012.
These weeds are regarded as the worst weeds in Australia because of their invasiveness, potential for spread, and economic and environmental impacts.
Under the National Weeds Strategy, 28 environmental weeds were identified National Environmental Alert Weeds. Alert Weeds are non-native plant species that are in the early stages of establishment and have the potential to become a significant threat to biodiversity if they are not managed.
Freshwater ecosystems are highly vulnerable to invasion by weeds. Many exotic plants have been accidentally or deliberately introduced into waterways in New South Wales, and have become widespread.
Some Australian native plants have become invasive in areas beyond their natural range or habitat. This is partly due to their popularity as ornamental plants, and partly due to landscape changes.
Many areas of native vegetation are protected in Australia. Always check native vegetation requirements before undertaking control of a weedy native plant.