nuphar

The beaver feeds on the roots of various water plants; for instance, a nuphar luteum, but chiefly on the bark of various trees, especially willow, cottonwood and birch.

A JOURNEY TO THE ROCKY MOUNTAINS IN 1839 1839

Their favourite food is the bark of the aspen, birch, and willow; they also eat the alder, but seldom touch any of the pine tribe unless from necessity; they are fond of the large roots of the _nuphar lutea_, and grow fat upon it, but it gives their flesh a strong rancid taste.

Narrative of a Journey to the Shores of the Polar Sea, in the Years 1819-20-21-22, Volume 1 John Franklin 1816