Family: Poaceae

Origin, Description & Uses:
Digitaria abyssinica, commonly known as African couch grass, is a perennial grass native to tropical and subtropical regions of Africa. It is a low-growing, mat-forming species that spreads aggressively by creeping stolons and underground rhizomes, creating dense turf. African couch grass has been used in some regions as a pasture grass for livestock and for erosion control due to its ability to quickly cover bare soil and tolerate grazing. Its resilience, rapid growth, and tolerance of a range of soil conditions have contributed to its intentional introduction outside its native range.

Risks & Threats:
African couch grass is naturalized on Kauaʻi and Maui, and although not currently documented in the flora of Oʻahu, it poses a high risk of further spread within the Hawaiian Islands. This species possesses several traits that are cause for concern, including rapid vegetative spread, formation of dense mats that outcompete other plants, and the ability to regenerate from small fragments. These characteristics allow it to displace native vegetation, alter groundcover composition, and reduce biodiversity in sensitive habitats. In tropical island ecosystems like Hawaiʻi, where many native plants evolved without aggressive grass competitors, African couch grass could detrimentally impact coastal, lowland, and disturbed natural areas. Its continued spread may make restoration efforts more difficult and costly, so planting is not recommended.

High Risk Traits:

• Naturalized elsewhere: Yes, including Hawaii
  
• Agricultural weed: Major weed of coffee, cotton, sugarcane, maize in East Africa; #1 weed in Kenyan coffee & Ugandan cotton
  
• Environmental weed: US Federal Noxious Weed
  
• Congeneric weed: Other Digitaria species are weeds
  
• Fire hazard: Forms dense mats; fire-resistant; emerges quickly after burning
  
• Shade tolerant: Tolerates shade but prefers sun
  
• Broad soil tolerance: Sandy loam, dry, muddy, disturbed soils
  
• Forms dense mats: Smothers other vegetation
  
• Reproduces by seed: Up to 26,000 seeds/m²
  
• Reproduces vegetatively: Any rhizome fragment with a node can regrow
  
• Unintentional dispersal: Roadsides, disturbed areas, vehicles
  
• Intentional dispersal: Planted for erosion control in South Africa
  
• Seed contaminant: Found in wheat samples
  
• Wind-dispersed: Seeds adapted for wind dispersal
  
• Prolific seed production: >1000 seeds/m²
  
• Tolerates disturbance: Benefits from cultivation, fire, rhizome fragmentation
  
• Broad climate suitability: Sea level to 3500m elevation

Low Risk Traits:

• Palatable to livestock – The grass is nutritious and well-liked by grazing animals, and grazing can help weaken it.
  
• Non-toxic to animals – No evidence of toxicity to livestock or other animals.
  
• Non-toxic to humans – Does not cause allergies or other toxic effects in people.
  
• Lacks physical defenses – No spines, thorns, or burrs.
  
• Wind-pollinated – Does not require specialist pollinators.
  
• Not water-dispersed – Dispersal is primarily by wind and gravity, not water.
  
• Not animal-dispersed – Lacks adaptations for internal or external dispersal by animals.
  
• No persistent seed bank – Seeds do not persist in soil for more than one year.
  
• Herbicide-susceptible – Can be effectively controlled using glyphosate, fluazifop-butyl, and sethoxydim.