UW Burke Herbarium species comparison

Leaves alternate, the submersed leathery, sub-terete, narrowly linear, 10-20 cm. long and 1-2 mm. broad; floating leaves long-petioled, leathery, ovate-lanceolate to ovate-elliptic, rounded to nearly cordate at the base, 5-10 cm. long and 2.5-5 cm. broad, 19- to 35-nerved;

stipules firm, fibrous, 4-10 cm. long.

Submersed leaves linear, sessile, 10-20 cm. long and 3-10 mm. broad, the mid-vein bordered by rows of air chambers; floating leaves with flattened petioles shorter than the blade, the blades firm, elliptic to oblong-elliptic, 4-8 cm. long and 10-20 mm. broad, 15- to 25-nerved;

stipules free, 1-3 cm. long, blunt.

: Flowers perfect, in densely-flowered spikes in 10-12 whorles, on stout peduncles 3-8 cm. long;

perianth of 4 clawed segments, each with an upturned, oval blade;

stamens 4, fused with the claws;

pistils 4, sessile.

Flowers in dense spikes 2-4 cm. long, on peduncles 3-8 cm. long;

perianth of 4 clawed segments, each with an upturned, oval blade;

stamens 4, fused with the claws;

pistils 4, sessile.

Achenes obliquely elliptic-obovoid, 3-5 mm. long, including the conical, stylar beak, rounded on the back.

Achenes obliquely and broadly obovate, 3-4 mm. long, sharply keeled on the back.