Family: Poaceae

Bromus diandrus, commonly known as ripgut grass, giant brome, or great brome, is an annual grass native to the Mediterranean region. It forms tall, upright clumps with coarse leaves and long, bristly seed heads that turn golden brown as they mature. The plant gets its nickname “ripgut” from its exceptionally stiff awns, which can be sharp enough to irritate livestock and wildlife. Although occasionally used for erosion control or forage in some regions, its rough texture and problematic seeds limit its usefulness.

In places where it becomes established, Bromus diandrus can spread aggressively in disturbed or open areas, outcompeting native plants and contributing to increased fire risk due to its dense, dry biomass. The barbed seeds can cause injury to pets, livestock, and wildlife by embedding in skin, eyes, or digestive tracts. Because of its ability to spread quickly and its harmful physical traits, ripgut grass can pose ecological and animal-health concerns where it is introduced.

High Risk Traits:

• Elevation range exceeds 2000 m, demonstrating environmental versatility
  
• Able to grow in tropical climates
  
• Naturalized on Kauai, Lanai, Maui, Hawaii and widely elsewhere
  
• Agricultural weed (competes with cereals and can sharp florets can injure livestock
  
• Environmental weed in Australia
  
• Other Bromus species are invasive
  
• Alternate host of cereal diseases
  
• Increases fire risk
  
• Shade-tolerant
  
• Tolerates many soil types
  
• Forms dense cover, excluding other vegetation
  
• Reproduces by seed
  
• Self-compatible
  
• Reaches maturity in one year (annual)
  
• Seeds dispersed by wind, attached to clothing or animal fur and internally by grazing animals
  
• Seeds can become a contaminant of cereals or in wool
  
• Prolific seed production
  
• Seeds persist for 2-3 years
  
• Tolerates mowing but not fire

Low Risk Traits:

• Palatable to grazing animals (when young)
  
• Not reported to spread vegetatively
  
• Herbicides provide effective control