Peltandra virginica, the green arrow arum (or Tuckahoe) looks similar in leaf shape to Sagittaria species, the arrowheads, but this bog plant is more fleshy, waxy and robust. The veins on the leaf have a beautiful pattern up close, and are very different to that of the Sagittaria arrowheads.
The pic below illustrates what I initially confused it with! The veins on arrowheads branch outwards from a central point, looking like legs spreading out from a spider's body:
