Source : Webster's Revised Unabridged Dictionary (1913)

Lucern \Lu"cern\, n. [F. luzerne.] (Bot.)
   A leguminous plant ({Medicago sativa}), having bluish purple
   cloverlike flowers, cultivated for fodder; -- called also
   {alfalfa}. [Written also {lucerne}.]

Alfalfa \Al*fal"fa\, n. [Sp.] (Bot.)
   The lucern ({Medicago sativa}); -- so called in California,
   Texas, etc.

Source : WordNet®

Medicago sativa
     n : important European leguminous forage plant with trifoliate
         leaves and blue-violet flowers grown widely as a pasture
         and hay crop [syn: {alfalfa}, {lucerne}]