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Much like no. 5 [Sparganium angustifolium Michx.], but with broader (6–12 mm), flat, more coarsely veined lvs, the basal ones ± V-shaped in section below; bracts and upper lvs not dilated at base except by the scarious margins; pistillate heads 1.5–2(–2.5) cm thick when ripe; 2n=30. In quiet water; circumboreal at high latitudes, s. to N. Engl., N.Y., Man., Colo., and Calif. Our plants, and most others from the conterminous U.S. and s. Can., belong to var. multipedunculatum (Morong) Reveal. (S. multipedunculatum) The more boreal and Eurasian var. emersum is more emergent, with larger heads and more keeled basal lvs. (S. simplex)
Stems emersed, erect, 30-70 cm tall, slender. Leaves 40-80 cm, aerial or floating, lower keeled on abaxial side. Racemes 10-20 cm; male heads 4-8, distinctly separate from female ones; female heads 3 or 4, relatively widely separated, sessile or lowest 1 or 2 pedunculate. Male flowers: perianth segments linear or spatulate, 2-2.5 mm, lobate at apex; filaments ca. 4 mm; anthers oblong, ca. 1.6 × 0.4 mm. Female flowers: perianth segments spatulate, ca. 3.5 mm, lobate at apex; ovary with short stalk; styles ca. 1 mm; stigmas 1.5-1.8 mm. Fruit fusiform. Fl. and fr. Jun-Oct. 2n = 30.
