Sparganium natans L.

Stems usually long and floating, varying to erect and 1–3 dm; lvs thin, flat, 2–7 mm wide, much elongate when floating; pistillate heads 1–3, axillary, sessile or the lowest rarely short-peduncled, 1 cm thick when ripe; tep narrowly spatulate, erose at the tip, reaching beyond the middle of the fr; achene sessile or nearly so, dull greenish or brownish, the body elliptic-obovoid, 3–4 mm, scarcely constricted, acute, the slender beak 0.5–1.5 mm; staminate head normally 1, separate; anthers oblong, 0.3–0.8 mm; 2n=30. In shallow water; circumboreal, s. to N.J., Pa., n. Ind., and N.M. (S. minimum)