Family: Poaceae

Origin, Description & Uses:
Paspalum conjugatum, commonly known as Hilo grass, is a creeping perennial grass native to tropical and subtropical regions of the Americas. It was introduced to Hawaiʻi in the 1800s and quickly spread throughout the islands. Today, it is naturalized on all of the main Hawaiian Islands except Niʻihau and Kahoʻolawe, where it commonly grows in moist to wet disturbed habitats such as roadsides, pastures, lawns, and open fields from low to mid elevations. Hilo grass forms dense mats with spreading stems that root at the nodes, allowing it to rapidly cover bare ground. Because of its vigorous growth and tolerance of wet conditions, it has been used as a pasture grass, groundcover, and for erosion control in tropical areas.

Risks & Threats:
Hilo grass is naturalized in Hawaiʻi and possesses traits that are cause for concern in tropical island ecosystems. Its aggressive spreading habit enables it to form dense carpets that can outcompete native vegetation, alter understory plant communities, and dominate disturbed or unmanaged areas. The species spreads readily through both seeds and creeping stems, making it difficult to control once established. Its ability to thrive in moist environments allows it to invade wetlands, forest edges, agricultural lands, and other sensitive habitats. Because Paspalum conjugatum may negatively impact native biodiversity and ecosystem function, it is considered a high risk species for Hawaiʻi. When possible, choosing low risk or native groundcover and pasture alternatives is recommended to help protect Hawaiʻi’s unique environments.

High Risk Traits:

• Naturalized and weedy in tropical regions worldwide
  
• Naturalized on Kaua'i, O'ahu, Molokai, Lana'i, Maui, and Hawai'i.
  
• Agricultural weed (e.g., in guaraná plantations, Hawaii)
  
• Environmental weed (displaces native forests)
  
• Congeneric species are serious weeds
  
• Forms dense ground cover, smothering other plants
  
• Shade tolerant
  
• Tolerates a wide range of soil conditions
  
• Reproduces by seeds and vegetatively via stolons
  
• Produces viable seeds, contributing to a soil seed bank
  
• Propagules dispersed by wind, water, animals (sticky fruits), and as a produce contaminant
  
• Prolific seed production (>1000/m²)
  
• Persistent seed bank (viable >1 year)
  
• Tolerates defoliation, grazing, and disturbance

Low Risk Traits:

• No spines, thorns, or burrs
  
• Palatable to grazing animals
  
• Not toxic to animals or humans
  
• Can be controlled with herbicides