Calla palustris.

Botanical name: 

Calla palustris Linn. Aroideae. Water Arum. Water Dragon.

Europe, Northern Asia and North America. The rootstocks of this plant yield eatable starch, prepared by drying and grinding them and then heating the powder until the acrid properties are dissipated.

Sturtevant's Edible Plants of the World, 1919, was edited by U. P. Hedrick.