Archemora rigida

from The Collaborative International Dictionary of English v.0.48

Cowbane \Cow"bane`\ (kou"b[=a]n`), n. (Bot.)
   A poisonous umbelliferous plant; in England, the {Cicuta
   virosa}; in the United States, the {Cicuta maculata} and the
   {Archemora rigida}. See {Water hemlock}.
   [1913 Webster]