alfalfa          
Medicago sativa   

Identifying Characteristics:

Seed:  kidney shaped, size varies between 2.0 to 2.5 mm long and 1.3 to 1.6 mm wide, color from green to light brown

Seedling:  trifoliate leaflets,  serrations on the top 1/3 of each leaflet

Mature Plant:  erect growth habit, large stipules, flower is generally purple, but varying cultivars may have yellow or white flowers, flowers arranged in round clusters 

Method of Propagation: seed 

Life Cycle: cool-season perennial 

Similar Species:sweetclover – decipher based on leaf serrations and flower arrangement 

References: Abaye, A. Ozzie. "Identification & Adaption: Common Grasses, Legumes & Non-leguminous Forbs of the Eastern United States."
Moore, Kenneth J. “Compendium of Common Forages.” From “Forages: An Introduction to Grassland Agriculture.”