The Collaborative International Dictionary of English v.0.48:

Lucerne \Lu"cerne\, n. (Bot.)
   See Lucern, the plant.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

lucerne
    n 1: important European leguminous forage plant with trifoliate
         leaves and blue-violet flowers grown widely as a pasture
         and hay crop [syn: alfalfa, lucerne, Medicago sativa]