The Collaborative International Dictionary of English v.0.48:

Culverkey \Cul"ver*key`\ (-k?`), n.
   1. A bunch of the keys or samaras of the ash tree. --Wright.
      [1913 Webster]

   2. An English meadow plant, perhaps the columbine or the
      bluebell squill (Scilla nutans). [Obs.]
      [1913 Webster]

            A girl cropping culverkeys and cowslips to make
            garlands.                             --Walton.
      [1913 Webster] Culver's physic