1. Acacia mearnsii
 |
Acacia mearnsii |
Black wattle (Acacia mearnsii) is an evergreen plant that can reach heights of up to 20 meters. In addition to producing a large number of seeds and growing robustly, this species also generates many lateral roots that compete with native species, leading to the formation of monoculture forests.
Common Name: Black Wattle
2. Ardisia elliptica
Ardisia elliptica is a fast-growing evergreen plant that thrives in shaded areas, forming dense monoculture forests that hinder the growth of all other plant species.
Common Name: Ardisia
3. Arundo donax
 |
Arundo donax |
Spanish reed (Arundo donax) is a perennial herbaceous plant that has been widely introduced to temperate and subtropical regions. Once established, it forms dense monoculture forests that compete with and diminish native plant communities, altering their habitats. Spanish reed also poses threats of wildfires and flooding.
Common Name: Spanish Reed
4. Cecropia peltata
Cecropia trees are native to tropical America and have been introduced to regions such as Cameroon, Côte d’Ivoire, and Malaysia, where they have become a dangerous invasive species. Cecropia spreads in disturbed areas, lava flows, and open forests. In Cameroon, it competes with a related species, Musanga cecropioides.
Common Name: Cecropia Tree
5. Chromolaena odorata
 |
Chromolaena odorata |
Chromolaena odorata, commonly known as Siam weed, is a fast-growing perennial shrub that spreads through wind-dispersed seeds and is often found in open, well-drained areas. It is commonly encountered in grasslands and agricultural fields across tropical Africa and Asia. Siam weed is highly flammable.
Common Name: Siam Weed
6. Cinchona pubescens
Cinchona, known for its role in producing quinine, invades both forests and open land, with seeds dispersed by the wind, competing for space and overshadowing native vegetation.
Common Name: Cinchona
7. Clidemia hirta
 |
Clidemia hirta |
Saphony grass (Clidemia hirta) is a toxic shrub that can grow up to 2 meters tall in grasslands and forests. It is a rapidly growing invasive species that eliminates all other vegetation beneath its canopy.
Common Name: Saphony Grass
8. Euphorbia esula
Euphorbia esula is native to Europe and Asia and is now found worldwide, except in Australia. This aggressive invasive species eradicates native plants by overshadowing them, absorbing water and nutrients, and producing toxins that inhibit the growth of other species beneath its canopy.
Common Name: Euphorbia
9. Hedychium gardnerianum
 |
Hedychium gardnerianum |
Wild ginger (Hedychium gardnerianum) is a herbaceous plant that disperses its seeds through birds. It grows rapidly, obstructing coastal areas of streams, and spreads naturally from residential gardens.
Common Name: Wild Ginger
10. Hiptage benghalensis
Hiptage benghalensis is a climbing plant with white/yellow fragrant flowers. It thrives in warm temperate to tropical climates and is an invasive species in La Réunion and Mauritius. In Mauritius, it invades lowland forest areas. In Vietnam, it grows wild in forests and is used for medicinal purposes to treat wounds and fractures.
Common Name: Hiptage (Spider Plant)
11. Imperata cylindrica
 |
Imperata cylindrica |
Cogongrass (Imperata cylindrica) is a common grass species (C4 plant, native to the Old World) that thrives in hot conditions across many countries in Africa, the Sahara, and Southeast Asia. It appears as a weed in many Pacific islands and is found in numerous locations in Vietnam, growing in sunny areas and used as a cooling medicinal herb.
Common Name: Cogongrass
12. Lantana camara
Lantana camara is widely cultivated in tropical, subtropical, and temperate regions as an ornamental plant. It adapts and grows rapidly as a weed in grasslands and environments across about 50 countries. In Vietnam, it is cultivated in many areas and used for its medicinal properties to stop bleeding and disinfect.
Common Name: Lantana, Guava Flower
13. Leucaena leucocephala
 |
Leucaena leucocephala |
Leucaena (Leucaena leucocephala) is a thornless shrub that grows in dense thickets, competing and eliminating all other species. Its seeds are dispersed by rodents and birds. In Vietnam, it grows wild and is cultivated in many areas.
Common Name: Leucaena
14. Ligustrum robustum
Ligustrum robustum is an invasive species that poses a significant threat to the biodiversity of forests in La Réunion and Mauritius. Its ability to sprout, rapid growth, shade tolerance, and low mortality rate, along with its large number of seeds dispersed by birds, contribute to its invasive potential in pristine forest areas.
Common Name: Ligustrum
15. Lythrum salicaria
 |
Lythrum salicaria |
Purple loosestrife (Lythrum salicaria) is a perennial herbaceous plant that can grow up to 3 meters tall. This plant is a notorious invasive weed in North America and Canada. Purple loosestrife invades natural wetlands and disturbed areas, and once established, it becomes a strong competitor, displacing native plant species and altering habitats.
Common Name: Purple Loosestrife
16. Melaleuca quinquenervia
Melaleuca quinquenervia, commonly known as paperbark tree, is a tall tree native to Eastern Australia, New Guinea, and New Caledonia, which invades open swampy areas.
Common Name: Paperbark Tree
17. Miconia calvescens
 |
Miconia calvescens |
Miconia (Miconia calvescens) is a dominant invasive species found in tropical islands of the Cook Islands and Hawaii (USA), where it was introduced as an ornamental plant.
Common Name: Miconia
18. Mikania micrantha
Mikania (Mikania micrantha) is a sprawling climbing plant that thrives in nutrient-rich and high-moisture environments.
Common Name: Mikania
19. Mimosa pigra
 |
Mimosa pigra |
Mimosa pigra is an aggressive invasive plant that grows in wetlands and tropical regions. It can outcompete native species and disrupt local ecosystems.
Common Name: Mimosa
1. Mimosa pigra
The Giant Sensitive Plant is a shrub species with a woody stem that grows tall, forming dense and impenetrable thickets in seasonal wetland regions of tropical and subtropical areas. This plant originates from the tropical regions of the Americas.
2. Myrica faya
The Hawaiian Dragon Tree is an evergreen shrub species that was introduced to Hawaii in the late 1800s for ornamental purposes. Today, it can be found on most of the major islands in Hawaii. Once established and adapted, it forms dense stands that hinder the regeneration of native species.
3. Opuntia stricta
 |
Opuntia stricta |
The Prickly Pear Cactus is a perennial plant native to the Northeastern United States, known for its high adaptability to dry conditions. It grows rapidly, forming dense prickly thickets that can injure livestock and restrict grazing. It competes aggressively with beneficial species in pastures.
4. Pinus pinaster
The Maritime Pine is a species native to the Mediterranean region that has been planted in temperate areas both within and outside its natural distribution for various reasons. It grows quickly wherever planted and, in many places, invades shrublands, forests, and natural grasslands.
5. Polygonum cuspidatum
 |
Polygonum cuspidatum |
Japanese Knotweed is a fast-growing herbaceous perennial that can form large clumps, reaching heights of 1 to 3 meters. Once established, it creates dense thickets that shade out and displace other plant species, reducing biodiversity and altering natural habitats.
6. Prosopis glandulosa
The Honey Mesquite is a woody, perennial shrub that sheds its leaves annually and grows rapidly to form dense thickets that aggressively compete with native species for water, potentially reducing species diversity beneath its canopy. The seeds of this plant can remain viable in the soil for up to 10 years.
7. Psidium cattleianum
 |
Psidium cattleianum |
The Strawberry Guava grows rapidly, forming dense thickets that shade out native tree species in tropical forest regions. This plant has severe impacts on native habitats in Mauritius and is regarded as one of the most dangerous invasive species in Hawaii, where it has invaded numerous different natural areas.
8. Pueraria montana
Montana Kudzu is a semi-woody vine from the kudzu genus that spreads rapidly, covering the ground and other plants. It has been reported to invade 2 to 3 million hectares in the eastern United States, causing an estimated annual crop loss of up to $500 million.
9. Rubus ellipticus
 |
Rubus ellipticus |
The Himalayan Blackberry is a thorny shrub that invades native forests. It spreads through underground shoots and seeds that are dispersed by birds and seed-eating mammals. The Himalayan Blackberry causes significant harm in Hawaii, where it has been competing with the native Hawaiian Blackberry (Rubus hawaiiensis).
10. Schinus terebinthifolius
The Brazilian Pepper Tree is native to Argentina, Paraguay, and Brazil. It is a pioneer species in cultivated areas and also thrives in undisturbed soils. The Brazilian Pepper Tree is a strong invasive species, outcompeting many native plant species.
11. Spathodea campanulata
 |
Spathodea campanulata |
The African Tulip Tree is a shade-tolerant species with vibrant colors that invades abandoned agricultural lands and dense forests. It thrives in humid and wet areas from sea level to 1000 meters in elevation. This invasive species is harmful in Hawaii, Fiji, Polynesia, and Samoa, with seeds dispersed by wind and rapid germination.
12. Tamarix ramosissima
The Saltcedar is a shrub species native to Asia and Southeastern Europe. It has adapted well in the United States and Mexico. Saltcedar can grow in highly saline soils and readily proliferates along canals, causing blockages when water levels rise, leading to flooding.
13. Ulex europaeus
 |
Ulex europaeus |
Gorse is an evergreen, thorny shrub that grows in dense thickets. It is commonly found in cleared lands, grasslands, shrublands, forest edges, coastal areas, and wastelands. This species thrives and is difficult to eradicate once established.
14. Wedelia trilobata
The Creeping Daisy is a fast-growing herbaceous vine from Central America that forms dense patches, obstructing and hindering the regeneration of other plant species.
(The species in this list have been selected to illustrate the harmful impacts of invasive organisms. The absence of species from this list does not imply they are less dangerous.)
