Family: Fabaceae

Origin, Description & Uses
Medicago sativa (alfalfa, lucerne, violet-flower lucerne) is native to the Mediterranean region extending through Central Asia and Iran. It is a long-lived perennial legume that produces deep taproots, upright leafy stems, and clusters of small purple to violet flowers. Widely cultivated around the world, it is valued as a high-quality forage crop for livestock, an important source of hay and silage, and a nutrient-rich pasture plant. Because it fixes atmospheric nitrogen through a symbiotic relationship with soil bacteria, it is also commonly used as a cover crop and green manure to improve soil fertility and structure.

Risks & Threats
This species is naturalized across the Hawaiian Islands, including Kuaihelani (Midway Atoll), Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi. While useful in agriculture, Medicago sativa possesses traits that are cause for concern in natural ecosystems. It can persist and spread in disturbed habitats, forming dense stands that may compete with native vegetation. As a nitrogen-fixing plant, it can also alter soil nutrient levels, potentially changing ecosystem dynamics in ways that disadvantage native Hawaiian species adapted to low-nutrient conditions. Its ability to naturalize across multiple islands highlights its adaptability and potential ecological impact. Because of these risks, it could detrimentally impact tropical island ecosystems if it continues to spread beyond managed areas. Where available, choosing low-risk or native plant alternatives is recommended to help protect Hawaii’s unique ecosystems.

High Risk Traits:

• Broad climate suitability, and elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Naturalized in regions with tropical climates
  
• Naturalized on all main Hawaiian Islands and widely naturalized elsewhere
  
• Often regarded as an escaped, weedy plant of crops and disturbed natural areas, but generally innocuous or desirable plant
  
• Other Medicago species are invasive
  
• Allelopathic
  
• May cause bloat and other diseases of grazing animals, but generally a desired, palatable plant
  
• Tolerates many soil types (not limited by substrate)
  
• Reproduces by seeds and vegetatively by rhizomes
  
• Self-fertile varieties may exist
  
• Able to reach maturity in one growing season
  
• Seeds dispersed internally by animals, potentially as a crop contaminant and water and intentionally by people
  
• Seeds long lived, and may form a persistent seed bank
  
• Able to resprout after fire

Low Risk Traits:

• Despite reports of weediness, generally regarded as a desirable pasture plant
  
• Unarmed (no spines, thorns, or burrs)
  
• Provides fodder for livestock
  
• Relatively shade intolerant
  
• Sensitive to herbicides, which may provide effective control if removal is desired