Invasive plants in Australia are formally tracked through a government classification called Weeds of National Significance, and according to the Australian Government’s Department of Agriculture, Fisheries and Forestry, that list of 32 species was determined through an assessment process prioritizing invasiveness, potential for spread, and environmental, social, and economic impact. Prickly pear and blackberry, 2 of the earliest species added to the list, remain textbook examples of just how severe an invasive plant problem can become before it’s brought under control.
Prickly pear’s history in Australia is genuinely one of the most dramatic invasive species stories in the world. According to the National Museum of Australia, the cactus was first brought to the country with the First Fleet in 1788, and by the 1920s it had overtaken 60 million acres of land in New South Wales and Queensland, rendering huge stretches of farmland completely unusable. The solution came in 1926, when researchers released the Cactoblastis cactorum moth from Argentina, and by 1930 some 3 billion moth eggs had been delivered to landholders using a fleet of 7 trucks, with roughly 2,000 hatched larvae capable of destroying a single mature cactus plant by eating through its flesh and triggering rot.
That biological control effort remains one of the most celebrated success stories in invasive species management anywhere in the world, and by 1933, 80% of the previously infested land in Queensland and 50 to 60% in New South Wales had been reclaimed. Not every entry on this list has a solution nearly that effective, and several remain active, unresolved management challenges decades after their introduction. What follows covers 30 invasive plants in Australia, along with where each one grows and the data behind its spread.
Prickly Pear
Prickly pear, a group of cactus species collectively classified as a Weed of National Significance, produces flat, spiny pads and colorful fruit, having overtaken 60 million acres of Australian farmland by the 1920s before biological control brought it under management. Its spines can cause serious injury to livestock, native animals, and people, and dense stands can also provide cover for feral animals.
It’s found throughout all Australian states and territories, capable of growing in a wide range of soil types and climates receiving at least 150 millimeters of annual rainfall. Even small dropped segments and fruit can regrow into new plants, requiring careful cleanup of any removed material.
Blackberry
Blackberry produces thorny, arching canes and sweet, edible fruit that, according to ABC News reporting on Australia’s worst weeds, spreads quickly, resists control efforts, and creates prickly thickets that shelter invasive animals like rabbits and foxes. A leaf rust fungus is currently used as a biological control agent to slow its spread, though eradication remains unrealistic.
It grows throughout temperate regions of southeastern Australia, forming dense thickets along waterways and disturbed pastureland that displace native vegetation.
Gorse
Gorse produces dense, spiny, evergreen growth topped with bright yellow flowers, originally introduced as a hedging plant before becoming a major agricultural weed throughout Tasmania and Victoria. Its sharp spines make manual removal genuinely difficult, and its seeds remain viable in the soil for decades.
It grows throughout cool, temperate regions of southeastern Australia, now dominating large stretches of pasture and disturbed land where it was once planted deliberately as a living fence.
Scotch Broom
Scotch broom produces bright yellow, pea-like flowers on a dense, woody shrub that spreads aggressively through long-lived seed banks in the soil. Its rapid colonization of disturbed and burned land has made it a persistent problem in cooler parts of the country.
It grows throughout temperate highland regions of southeastern Australia, forming dense stands that crowd out native shrubs and grasses.
Lantana
Lantana produces clusters of small, multicolored flowers on a spiny, sprawling shrub considered one of the worst weeds in Australia given its toxicity to livestock and its capacity to smother native vegetation. Its foliage and unripe berries can poison grazing animals.
It grows throughout coastal and subtropical eastern Australia, forming dense, thorny thickets that displace native understory plants across a huge range of habitat types.
Bitou Bush
Bitou bush produces bright yellow, daisy-like flowers on a sprawling coastal shrub originally introduced to stabilize sand dunes after mining operations. Its dense growth has instead displaced native coastal vegetation across huge stretches of shoreline.
It grows throughout coastal areas of eastern Australia, particularly favoring the sandy dune habitat it was originally planted to protect.
Boneseed
Boneseed, a close relative of bitou bush, produces similar bright yellow flowers on a shrub that invades a wider range of habitat types beyond just coastal dunes. Both species are classified together under the same Weed of National Significance listing given their shared invasive characteristics.
It grows throughout temperate coastal and inland areas of southern Australia, forming dense stands in woodland and shrubland habitat.
Water Hyacinth
Water hyacinth produces rounded, glossy leaves atop inflated, spongy stems that keep the plant afloat, forming dense mats capable of covering an entire waterway’s surface. A single mat can double in coverage within roughly 2 weeks under warm, nutrient-rich conditions.
It grows throughout warm, slow-moving waterways across northern and eastern Australia, blocking light and oxygen from native aquatic plants and fish.
Salvinia
Salvinia produces small, floating, hairy leaves that form dense mats capable of covering an entire pond or slow-moving waterway within weeks. Its mats can grow thick enough to block sunlight to submerged native plants and deplete oxygen levels in the water below.
It grows throughout warmer waterways across northern and eastern Australia, spreading readily whenever fragments are transported on boats or other equipment.
Parthenium Weed
Parthenium weed produces small white flower heads on a fast-growing annual capable of causing severe allergic skin reactions and respiratory problems in people exposed to its pollen and foliage. Its rapid spread through cattle-grazing regions has made it a significant agricultural and public health concern.
It grows throughout inland Queensland and parts of other northern states, particularly along roadsides and disturbed grazing land.
Mimosa
Mimosa, also called giant sensitive plant, produces fern-like, sensitive leaves that fold when touched, on a thorny shrub capable of forming impenetrable thickets across wetland floodplains. Its dense growth blocks access for both wildlife and livestock across huge areas of tropical wetland.
It grows throughout tropical floodplains of northern Australia, particularly the Northern Territory, where it has displaced native wetland vegetation across thousands of hectares.
Rubber Vine
Rubber vine produces showy, funnel-shaped pink-white flowers on a fast-growing, milky-sapped vine capable of smothering native trees along tropical waterways. Every part of the plant is toxic to livestock, adding a genuine safety concern beyond its aggressive spread.
It grows throughout tropical northern Australia, forming dense curtains over riverside vegetation that block light and access to native riparian habitat.
Prickly Acacia
Prickly acacia produces small, fragrant yellow flower balls on a thorny tree capable of forming dense thickets across grazing land. Its long, sharp thorns make affected pastureland genuinely difficult and dangerous for livestock and workers to move through.
It grows throughout inland Queensland and other parts of northern Australia, displacing native grassland and woodland vegetation across extensive grazing regions.
Mesquite
Mesquite produces long, straight seed pods and a deep taproot capable of reaching groundwater far below the surface, giving the tree exceptional drought tolerance in the arid regions where it establishes. Its thorny, dense thickets can render grazing land unusable.
It grows throughout arid inland regions of Australia, particularly Western Australia and Queensland, forming impenetrable stands on grazing land.
Athel Pine
Athel pine, despite its name, is a flowering tree rather than a true conifer, producing fine, scale-like foliage and small pink flowers on a species that consumes enormous quantities of groundwater along the arid waterways it invades. Its deep roots can lower the water table enough to affect surrounding native vegetation.
It grows along desert waterways in central Australia, forming dense stands that alter the natural flow and salinity of the rivers it colonizes.
Serrated Tussock
Serrated tussock produces fine, tightly rolled grass blades that cattle and sheep generally avoid grazing, allowing the plant to spread largely unchecked across pastureland. A single plant can produce well over 100,000 seeds in a season, carried considerable distances by wind.
It grows throughout temperate grazing regions of southeastern Australia, capable of completely displacing productive pasture grass within just a few seasons of establishment.
Chilean Needle Grass
Chilean needle grass produces sharp, barbed seeds capable of penetrating skin, eyes, and even internal organs of grazing livestock, causing serious injury beyond its simple competitive impact on pasture. Its seeds also contaminate wool, reducing its commercial value.
It grows throughout temperate grazing regions of southeastern Australia, spreading readily via seeds that cling to animals, vehicles, and clothing.
Fireweed
Fireweed produces small, bright yellow, daisy-like flowers on a fast-growing annual toxic to grazing livestock if consumed in quantity over time. Its rapid spread through pastureland has made it a significant concern for the cattle industry in affected regions.
It grows throughout coastal pastureland in eastern Australia, particularly New South Wales, spreading rapidly through wind-dispersed seed.
Bridal Creeper
Bridal creeper produces glossy, heart-shaped leaves on a twining vine that forms a dense underground mat of tuberous roots, making it exceptionally difficult to remove by hand. Its climbing growth can smother native shrubs and groundcover entirely.
It grows throughout southern Australia, particularly favoring woodland and coastal scrub habitat where its underground tuber mat outcompetes native root systems for space and moisture.
Willow
Willow, excluding a handful of specifically exempted ornamental varieties, produces extensive root systems along waterways that can alter natural stream flow and outcompete native riparian vegetation. Fallen branches root readily in wet soil, allowing the tree to spread vegetatively along an entire waterway.
It grows throughout temperate waterways across southeastern Australia, and several species are actively targeted for removal specifically to restore natural water flow patterns.
Alligator Weed
Alligator weed produces small white flower clusters on a plant capable of growing in wet soil, shallow water, or fully submerged conditions, giving it an unusually broad range of habitats it can invade. Its dense mats can clog irrigation channels and waterways.
It grows throughout wetland and waterway margins in eastern Australia, spreading readily from even small fragmented pieces of stem or root.
Cat’s Claw Creeper
Cat’s claw creeper produces small, hooked, claw-like tendrils that let it grip bark and structures, forming a dense canopy capable of smothering an entire host tree within a few seasons. Its thick, tuberous root system stores enough energy to regrow rapidly even after being cut back.
It grows throughout coastal and subtropical eastern Australia, commonly escaping from ornamental plantings into surrounding forest.
Madeira Vine
Madeira vine produces glossy, heart-shaped leaves and small, potato-like tubers along its stem, each one capable of dropping off and sprouting an entirely new plant. That prolific tuber production makes the vine exceptionally difficult to eradicate once established.
It grows throughout coastal and subtropical eastern Australia, smothering native tree canopies under the sheer weight of its dense growth.
Asparagus Fern
Asparagus fern, covering several related species listed together as a Weed of National Significance, produces feathery, fern-like foliage on a climbing or sprawling plant that forms a dense underground tuber mat similar to bridal creeper. Its berries are readily spread by birds into native bushland.
It grows throughout coastal and temperate regions of southern and eastern Australia, smothering native groundcover and preventing native seedling establishment.
African Boxthorn
African boxthorn produces dense, thorny growth and small orange-red berries on a shrub that provides cover for rabbits and foxes, complicating pest animal control alongside its own invasive spread. Its thorns make manual removal a genuinely difficult task.
It grows throughout coastal and inland areas across much of southern Australia, forming impenetrable thickets in pastureland and disturbed coastal habitat.
Bellyache Bush
Bellyache bush produces clusters of small red flowers on a shrub whose seeds and sap are toxic enough to cause serious illness in livestock and humans if ingested. Its rapid growth and prolific seeding have made it a significant concern in tropical grazing regions.
It grows throughout tropical northern Australia, particularly Queensland and the Northern Territory, spreading readily through disturbed grazing land.
Gamba Grass
Gamba grass produces towering stands that can reach over 10 feet tall, creating a fuel load dramatically higher than native grasses and significantly increasing the intensity of tropical wildfires. Fires burning through gamba grass stands can reach temperatures hot enough to kill mature native trees that would easily survive a typical grass fire.
It grows throughout tropical northern Australia, particularly the Northern Territory, transforming savanna woodland into far more fire-prone grassland over time.
Silverleaf Nightshade
Silverleaf nightshade produces small purple flowers and yellow, tomato-like berries on a deeply taprooted perennial toxic to livestock if eaten. Its extensive root system allows it to regenerate readily even after herbicide treatment or cultivation.
It grows throughout agricultural regions of southern and eastern Australia, competing directly with crops and pasture for water and nutrients.
Parkinsonia
Parkinsonia produces small, fragrant yellow flowers on a thorny, drought-tolerant shrub capable of forming dense, impenetrable thickets along waterways in arid and tropical regions. Its thorns make affected land genuinely dangerous for livestock and workers to navigate.
It grows throughout northern and central Australia, forming dense stands along watercourses that restrict wildlife movement and water access.
Pond Apple
Pond apple produces glossy leaves and a fruit resembling a custard apple on a wetland tree capable of forming dense monocultures in tropical swamp habitat. Its fruit floats and disperses readily along waterways, allowing rapid spread downstream from any established population.
It grows throughout tropical wetlands in northern Queensland, displacing native mangrove and swamp forest vegetation across significant areas of critical habitat.
Conclusion
Invasive plants in Australia can spread across forests, grasslands, wetlands, farmland, roadsides, and urban areas. They may compete with native plants for water, nutrients, sunlight, and space, while some species can also alter habitats and affect native wildlife.
Learning to identify invasive plants is an important step in preventing their spread. Early detection and regular monitoring can help locate new infestations before they become widely established, while appropriate control methods can reduce their impact on native vegetation and ecosystems.
Protecting Australia’s diverse landscapes requires ongoing attention from landowners, gardeners, farmers, conservation groups, and local communities. Choosing suitable non-invasive plants, preventing the movement of seeds and plant material, and managing established infestations can help protect native ecosystems for the future.