The Collaborative International Dictionary of English v.0.48:

Culver's physic \Cul"ver's phys"ic\, or Culver's root \Cul"ver's
root`\ [So called after a Dr. Culver, who used it.] (Bot.)
   The root of a handsome erect herb (Leptandra Virginica syn.
   Veronica Virginica) common in most moist woods of North
   America, used as an active cathartic and emetic; also, the
   plant itself.
   [Webster 1913 Suppl.]