“A weed is any plant that requires some form of action to reduce its effect on the economy, the environment, human health and amenity.” – D.Montoya 2012. 

Weeds come in various shapes, sizes and classifications. Classifications include invasive weeds, noxious weeds and exotic weeds. These classifications often overlap. Alternatively, a weed is any plant that does not belong or is not wanted in its current location. 

The impact of weeds is primarily the intense competition they bring to the existing environment. This aggressive competition often swallows local species and causes mass degradation of the biodiversity and ecology of an entire area. 

Weeds can, however, also be harmful to animals, agriculture and industry. These weeds are often labelled as noxious as they specifically affect local processes and result in a high economic cost. Noxious weeds are plants known due to their invasive tactics and difficulty controlling. Notable species are Patterson’s Curse - Echium plantagineum, Prickly Pear - Opuntia leucotricha and Fire Weed - Senecio madagascariensis.

Invasive weeds are plants that have been introduced into an environment, suited for their optimum growth. These can be both native and exotic, caused when plants are moved around the country from machinery, horticulture and trade. Notable species include Boxthorn - Lycium ferocissimum, various cacti species and various water species. This is due to Australia hosting a variety of environments often aligning with other countries with similar biomes. This results in Australia becoming a prime location for invasive species infestations. 

Exotic weeds are plants from overseas whereby they have been brought to Australia and escaped containment. These weeds have catastrophic effects on the native environment as they have no naturally occurring control mechanisms and often find themselves in environments better suited for their optimum growth. This leads to mass invasive populations whereby even after eradication the previous landscape is non-existent.