Arrowhead tuber
Arrowhead, or sagittaria, are aquatic plants whose members go by a variety of common names, including duck potato, iz-ze-kn, katniss, kuwai (くわい in Japanese), swan potato, tule potato, and wapato (or wapatoo). Most are native to South, Central, and North America, but there are also some from Europe and Asia.
Not to be confused with arrowroot.