Family: Acanthaceae

Origin, Description & Uses:
Hygrophila polysperma, commonly known as East Indian swampweed, is an aquatic plant native to parts of South and Southeast Asia. It is a fast-growing, herbaceous species typically found in freshwater habitats such as rivers, lakes, and wetlands. This plant has long, slender stems with small, lance-shaped leaves that can vary in color from green to reddish under certain conditions. Due to its rapid growth and adaptability, it is popular in the aquarium trade, where it is valued for its ability to oxygenate water, absorb excess nutrients, and provide cover for fish and other aquatic organisms.

Risks & Threats:
Although Hygrophila polysperma is not currently known to be naturalized in the Hawaiian Islands, it possesses several traits that raise concern. Its rapid growth rate, ability to reproduce from small fragments, and tolerance of a wide range of environmental conditions make it highly invasive in suitable habitats. In other regions, it has formed dense mats that outcompete native aquatic plants, alter water flow, and degrade habitat for fish and wildlife. If introduced into Hawaii’s waterways, it could detrimentally impact sensitive tropical island ecosystems. For these reasons, it is recommended to avoid planting or releasing this species and instead choose a low-risk or native alternative for aquaria and water gardens.

High Risk Traits:

• Broad climate tolerance (4-30°C)
  
• Native to tropical/subtropical Asia
  
• Repeated introductions via aquarium trade
  
• Naturalized in the US (Texas, Florida) and Mexico
  
• Environmental weed: forms dense mats, displaces natives, causes anoxia
  
• Congeneric weed (H. costata weedy in Australia)
  
• Unpalatable to grazing fish (grass carp)
  
• Shade tolerant
  
• Forms dense thickets
  
• Aquatic noxious weed (multiple US states)
  
• Produces viable seed
  
• Reproduces via vegetative fragments
  
• Generates in ≤1 year; rapid expansion
  
• Propagules spread by water, recreation, and intentional sale
  
• Difficult to control with herbicides; resistant and expensive
  
• Tolerates mutilation (fragmentation promotes spread)

Low Risk Traits:

• No spines, thorns, burrs, or allelopathy
  
• Not toxic
  
• No fire hazard (aquatic)
  
• Not dispersed by wind, birds, animals, or as a produce contaminant