Family: Fabaceae

Origin, Description & Uses
Stylosanthes guianensis is native to a broad range from Mexico through Central America and into South Tropical America. It is a warm-climate, perennial legume that typically grows as a low, branching herb or subshrub, often forming dense ground cover in open grasslands, disturbed sites, and agricultural areas. Like other Stylosanthes species, it has been introduced in many tropical regions for its value as a forage and pasture improvement plant due to its nitrogen-fixing ability, which can help improve soil fertility. It has also been used in erosion control and land rehabilitation projects in tropical and subtropical environments.

Risks & Threats
This species is naturalized in Hawaiʻi, with established populations on Kauaʻi and reports of potentially naturalizing on Oʻahu and Molokaʻi. As a nitrogen-fixing legume with strong growth and persistence in disturbed habitats, it possesses traits that are cause for concern, including the ability to spread into open landscapes, compete with low-growing native vegetation, and alter soil nutrient dynamics in ways that can disadvantage native plant communities. In tropical island ecosystems, these changes can have long-term detrimental impacts on biodiversity and ecosystem function. Because of these risks, Stylosanthes guianensis should be carefully managed, and its use discouraged in favor of low-risk or native alternatives when available. Where it is already present, efforts should focus on preventing further planting and limiting spread into new areas where it is not yet widely established to reduce additional ecological impacts.

High Risk Traits:

• Naturalized beyond native range and has congeneric weeds
  
• Kaua'i (Naturalized); O'ahu and Molokai (Potentially naturalizing)
  
• Allelopathic and hosts pests/pathogens
  
• Tolerates varied soils, fixes nitrogen, and self-compatible
  
• Fast maturity (1 year) with viable, persistent seed bank
  
• Dispersed intentionally by people, externally by animals, via gut passage, and unintentionally via hooked pods
  
• Benefits from fire, cultivation, or mutilation

Low Risk Traits:

• Not weedy, or invasive in natural/agricultural systems
  
• No spines, thorns, burrs, or climbing/smothering habit
  
• Not toxic, parasitic, or fire-promoting
  
• Palatable and not shade-tolerant
  
• No vegetative reproduction, water/wind/bird dispersal, or produce contamination
  
• Low seed output and no dense thicket formation