aka watato, wapati, katniss, duck potato (and many more); Sagittaria latifolia; Alismataceae (water-plantain family)
I found a stand of arrowheads in an unlikely place: halfway up one of the rocky bluffs that jut into the Potomac near the trail. This bluff had a lot of pockets, though, including one that looked wide and deep enough to stay wet (from flood or rain) year ’round. And so, a small rocky pond 15 feet above river level.
Common arrowhead is found in most of the US and Canada. It’s listed as both potentially invasive (by the Southern Weed Science Society) and endangered (by the state of Illinois). The rhizomes were eaten by Native Americans (also by muskrats and beavers), and the seeds are eaten by ducks.