The Collaborative International Dictionary of English v.0.48:

Deergrass \Deer"grass`\, n. (Bot.)
   An American genus (Rhexia) of perennial herbs, with
   opposite leaves, and showy flowers (usually bright purple),
   with four petals and eight stamens, -- the only genus of the
   order Melastomace[ae] inhabiting a temperate clime.
   [1913 Webster]