The Collaborative International Dictionary of English v.0.48:

Guaco \Gua"co\, n. [Sp.] (Bot.)
      (a) A plant (Aristolochia anguicida) of Carthagena, used
          as an antidote to serpent bites. --Lindley.
      (b) The Mikania Guaco, of Brazil, used for the same
          purpose.
          [1913 Webster]