Family: Poaceae

Origin, Description & Uses
Paspalum dilatatum, commonly known as dallis grass, is a perennial bunchgrass native to southeastern and southern Brazil through northern Argentina. It was introduced to many tropical and subtropical regions as a forage and pasture grass because of its rapid growth, tolerance of a range of environmental conditions, and value for grazing livestock. Dallis grass forms dense clumps with tall flowering stems and narrow green leaves, and it is commonly found in lawns, roadsides, fields, and disturbed areas. In Hawaiʻi, it has become naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island, where it is now common in wet to dry grasslands, pastures, and along roadsides from low elevations up to about 1,620 meters. It was first collected on Hawaiʻi Island in 1911.

Risks & Threats
Dallis grass is naturalized in Hawaiʻi and possesses traits that are cause for concern in tropical island ecosystems. It spreads efficiently by seed and can form dense stands that compete with native vegetation and other desirable plants for sunlight, water, and nutrients. Its adaptability to a wide range of moisture conditions and disturbed habitats allows it to expand into grasslands, open natural areas, and managed landscapes. Dense infestations may alter habitat structure, reduce biodiversity, and increase management challenges in agricultural and conservation settings. Because this species could detrimentally impact tropical island ecosystems, caution is recommended when considering its use. Choosing low risk or native alternatives is encouraged whenever suitable alternatives are available.

High Risk Traits:

• Widely naturalized beyond native range (Hawaii, California, New Zealand, subtropics)
  
• Naturalized on Kaua'i, O'ahu, Molokai, Lana'i, Maui, and Hawai'i.
  
• Serious agricultural weed (Australia, Philippines, Brazil, Colombia, Taiwan)
  
• Weed in lawns and corn crops
  
• Congeneric weeds (P. conjugatum, P. distichum) are serious weeds
  
• Host to 65 fungi and a virus affecting corn and wheat
  
• Apomictic (reproduces without cross-pollination)
  
• Produces viable seed
  
• Prolific seed production (~220,000 seeds/lb)
  
• Persistent seed bank (viable >2 years)
  
• Regrows after grazing and mowing

Low Risk Traits:

• Limited climate suitability (fails below 13°C, low elevations)
  
• Not an environmental weed
  
• No spines, thorns, or burrs
  
• Not allelopathic or parasitic
  
• Palatable to grazing animals
  
• Non-toxic (unless fungus-infected)
  
• Not shade tolerant
  
• Slow vegetative spread (mainly by seed)