Calla palustris.

Botanical name: 

CALLA PALUSTRIS, L. Swamprobin. Canada and New York. Roots acrid and caustic like Arum, yet by drying, grinding, macerating and boiling, a fine meal and bread is made in Sweden, very palatable.

Medical Flora, or Manual of the Medical Botany of the United States of North America, Vol. 2, 1830, was written by C. S. Rafinesque.