The Collaborative International Dictionary of English v.0.48:

Lyme grass \Lyme" grass`\n. (Bot.)
   A coarse perennial grass of several species of Elymus, esp.
   Elymus Canadensis, and the European Elymus arenarius.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Elymus canadensis
    n 1: North American wild rye [syn: Canada wild rye, Elymus
         canadensis]