EN · European bur-reed, unbranched bur-reed
DE · Einfacher Igelkolben
LV · vienkāršā ežgalvīte
PL · jeżogłówka pojedyncza
https://en.wikipedia.org/wiki/Sparganium_emersum
The leaves are flat and straplike, sometimes with a triangular, keeled base that can help distinguish it from the similar Sparganium angustifolium.