Family: Salviniaceae

Origin, Description & Uses
Salvinia molesta (giant salvinia) is a free-floating aquatic fern native to southern and southeastern Brazil through northern Argentina (Corrientes). It is a hydroperennial species that thrives in warm, still or slow-moving freshwater habitats such as ponds, lakes, ditches, and wetlands. It forms dense, spreading mats of floating foliage made up of small, oval leaves covered in water-repellent hairs that keep the plant buoyant. While sometimes seen in the aquarium and ornamental water garden trade due to its rapid growth and ability to cover water surfaces, it is not a suitable ornamental plant and should never be intentionally used in cultivated water features.

Risks & Threats
This species is naturalized in Hawaiʻi (recorded on Kauaʻi, Oʻahu, and Hawaiʻi Island) and possesses traits that are cause for serious concern, including extremely rapid vegetative reproduction and the ability to form thick, continuous mats that blanket entire water bodies. These infestations block sunlight, suppress oxygen exchange, and quickly degrade freshwater habitat, severely impacting native aquatic plants, invertebrates, and fish. It can also clog irrigation systems, drainage canals, and reservoirs, creating major ecological and economic disruptions. Because of its aggressive growth and extreme difficulty of control once established, Salvinia molesta should never be cultivated, transported, or shared under any circumstances. Even small fragments can spread and establish new populations. Where it is already present, it requires active management to prevent further spread and limit ecological damage, and it is critical to avoid any new plantings or intentional use in ornamental water systems. Low-risk or native aquatic plants should always be chosen instead to protect tropical island ecosystems.

High Risk Traits:

• Highly adaptable to tropical, subtropical, and warm temperate climates
  
• Naturalized and weedy outside native range
  
• Causes severe environmental, agricultural, and recreational damage (clogs waterways, alters ecosystems)
  
• Congeneric species are also noxious weeds
  
• Tolerates shade
  
• Smothering growth habit; forms dense, thick mats (up to 3 ft deep, 96 sq miles)
  
• Aquatic fern (floating)
  
• Reproduces rapidly by vegetative fragmentation (doubles in 2.2 days)
  
• Dispersed unintentionally (boats, fishing gear) and intentionally (aquarium trade)
  
• Dispersed by wind, water, and externally by animals
  
• Dormant buds survive dry conditions up to 2 years
  
• Benefits from mutilation/cultivation (regenerates from fragments)
  
• No effective natural enemies in many invaded regions

Low Risk Traits:

• No spines, thorns, burrs, or allelopathic/parasitic traits
  
• Palatable to grazing animals (used as livestock forage)
  
• Not toxic to animals or humans
  
• No fire hazard (aquatic species)
  
• Sexually sterile (no viable seeds, no spore production)
  
• Herbicides provide effective control
  
• Biocontrol agents exist (e.g., Cyrtobagous salviniae)