The Collaborative International Dictionary of English v.0.48:

elephant-tusk \elephant-tusk\ n.
   an annual of the southern U.S. and Mexico (Proboscidea
   louisianica) having large whitish or yellowish flowers
   mottled with purple and a long curving beak.

   Syn: common unicorn plant, devil's claw, common devil's claw,
        proboscis flower, ram's horn, Proboscidea louisianica.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Proboscidea louisianica
    n 1: annual of southern United States to Mexico having large
         whitish or yellowish flowers mottled with purple and a long
         curving beak [syn: common unicorn plant, devil's claw,
         common devil's claw, elephant-tusk, proboscis flower,
         ram's horn, Proboscidea louisianica]