The Collaborative International Dictionary of English v.0.48:

Wapatoo \Wap"a*too`\, n. (Bot.)
   The edible tuber of a species of arrowhead (Sagittaria
   variabilis); -- so called by the Indians of Oregon. [Written
   also wappato.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wappato \Wap"pa*to\, n. (Bot.)
   See Wapatoo.
   [1913 Webster]