Invasive species of Australian origin

Perhaps the best known example of an Australian plant becoming an invasive species is the problematic introduction of Melaleuca quinquenervia into Florida. As with all Melaleuca species, M. quinquenervia seeds prolifically. In the absence of natural predators, it spread throughout southern Florida; at one time it was estimated that it had colonised 12% of southern Florida. The colonised area included a substantial proportion of the Everglades, an important national park and World Heritage Site. Attempts were made to control the spread by burning, but this only exacerbated the problem as it encouraged seed dispersal while failing to kill the trees. The spread of Melaleuca is now managed by a combination of regular herbicide treatment and the introduction of an Australian beetle as a biological control.

A number of Acacia species have become serious environmental pests after being introduced into southern Africa. The most troublesome species are Acacia cyclops and Acacia saligna. Both are Western Australian coastal wattles, introduced to help bind drifting sand dunes. They remain serious pests, but some controls have been introduced. In the case of Acacia saligna, the introduction of acacia seed weevils (Melanterius species) has achieved complete control. A lesser degree of control has been achieved for Acacia cyclops by the introduction of a gall rust fungus (Uromycladium species).

• Acaena novae-zelandiae is declared a noxious weed in the American states of Hawaii, California and Oregon.[1]
• Cupaniopsis anacardioides, the tuckeroo, has become an invasive weed along the coastline of Florida. The plant there is known as carrotwood.
• Eucalyptus globulus has spread rapidly as an invasive species since being introduced into California in the mid-19th century. Its colonization is reducing habitats for native species (often by type shift from grasslands or oak woodlands), and increasing the threats and spread of wildfires.
• Hakea sericea has colonised much of the Table Mountain fynbos since its introduction into South Africa.
• Imperata cylindrica
• Melia azedarach
• Pittosporum undulatum has become invasive in the Caribbean, Hawaii, southern Brazil and in the Azores.
• Schefflera actinophylla