Family: Poaceae

Origin, Description & Uses
Setaria sphacelata is native to tropical and southern Africa, including Madagascar, where it grows in open grasslands, disturbed sites, and seasonally wet areas. It is a robust, warm-season perennial grass that forms dense clumps and produces upright flowering spikes with characteristic bristly seed heads. This species has been introduced globally and is used in some regions as a pasture grass and for forage due to its high biomass production and ability to grow in a range of conditions, including poor or seasonally wet soils.

Risks & Threats
Setaria sphacelata is naturalized on Kauaʻi, Oʻahu, Maui, and Hawaiʻi Island, and possesses traits that are cause for concern in tropical island ecosystems. It spreads readily by seed, forms dense stands, and can compete aggressively with native vegetation and other desirable plants, particularly in disturbed habitats, roadsides, and grazing areas. Its persistence and rapid growth can alter plant community structure and reduce habitat quality for native species. Because of these impacts, it could detrimentally affect tropical island ecosystems if it continues to expand. When available, low-risk or native alternatives should be chosen instead. Where it is already established, efforts should focus on managing existing populations and preventing its use or spread into areas where it is not yet widespread to help minimize further negative impacts.

High Risk Traits:

• Broad tropical/subtropical climate suitability
  
• Naturalized in Hawaii, California, Galápagos, Australia
  
• Environmental weed; threatens native plant communities
  
• Congeneric species are invasive weeds
  
• Forms dense tussocks and root mats; suppresses other vegetation
  
• Toxic to livestock (oxalate poisoning under certain conditions)
  
• Host for fungal pathogens and insect pests
  
• Shade tolerant (60–70% yield at 50% shade)
  
• Tolerates a wide range of soil types
  
• Produces viable seed; establishes easily
  
• Hybridizes naturally and self-compatible
  
• Reproduces vegetatively (root splits, stolons, vivipary)
  
• Reaches reproductive stage in <1 year
  
• Intentionally spread by humans as forage
  
• Wind-dispersed seeds; colonizes disturbed areas
  
• Seeds survive livestock gut passage
  
• Prolific seed production in cultivation
  
• Tolerant of cutting, grazing, and fire

Low Risk Traits:

• No spines, thorns, or burrs
  
• Not toxic to humans
  
• No persistent seed bank (seeds short-lived in soil)
  
• No evidence of water, bird, or external animal dispersal
  
• Not a major agricultural/forestry weed (primarily a forage species)
  
• Natural enemies/pathogens present locally
  
• Controllable with herbicides