Family: Poaceae

Origin, Description & Uses:
Lolium multiflorum (annual ryegrass) is native to Europe, North Africa, and parts of temperate Asia. It is a fast-growing cool-season grass that forms dense tufts of bright green foliage and can reach up to 1–3 feet tall. It is widely used in agriculture as a forage crop for livestock, for temporary pasture improvement, erosion control, and as a cover crop to improve soil structure and reduce weed growth. Its rapid germination and ability to establish quickly in disturbed soils have made it a popular choice in temperate farming systems around the world.

Risks & Threats:
In Hawaiʻi, annual ryegrass is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island. It spreads readily through seed production and can persist in disturbed areas, roadsides, pastures, and open landscapes. This species possesses traits that are cause for concern, including rapid growth, high seed output, and the ability to outcompete slower-growing vegetation. In tropical island ecosystems, it could alter habitat structure, compete with native plants, and contribute to shifts in plant community composition, especially in disturbed or managed lands. Because of these risks, Lolium multiflorum could detrimentally impact Hawaiʻi’s ecosystems, and planting is discouraged where it may spread. When available, choosing a low-risk or native alternative is recommended to help protect Hawaiʻi’s unique biodiversity.

High Risk Traits:

• Naturalized beyond native range (including U.S. and Hawaii)
  
• Agricultural weed (small grains, corn, soybeans)
  
• Principal weed in several countries
  
• Congeneric weeds exist (L. temulentum, L. perenne)
  
• Creates fire hazard (dense dry stands burn readily)
  
• Tolerates wide range of soils
  
• Produces viable seed
  
• Hybridizes naturally
  
• Annual / short-lived perennial (1 year generation time)
  
• Propagules dispersed unintentionally (awns attach to traffic/animals)
  
• Intentionally dispersed by people (forage grass)
  
• Produce contaminant (e.g., hay)
  
• Wind-dispersed seeds
  
• Externally dispersed by animals (awns)
  
• Seeds survive gut passage (cattle)
  
• Prolific seed production
  
• Well controlled by herbicides (indicates weed status)

Low Risk Traits:

• Not toxic (high-quality forage)
  
• No allergy or human toxicity
  
• Shade intolerant
  
• Self-incompatible
  
• No vegetative reproduction
  
• No water or bird dispersal
  
• No persistent seed bank (>1 year; transient)
  
• Fire kills plants (though seeds may survive)