Aquatic and Wetland Vascular Plants of the Northern Great Plains
55. Potamogetonaceae, the Pondweed Family
1. Potamogeton L. -- Pondweed2. Potamogeton amplifolius Tuckerm. -- Largeleaf pondweed
Stems terete, 2-4 mm thick, simple or occasionally branched above, to 1 m long. Upper submersed leaves broadly lanceolate to ovate, falcately folded and often arcuate, 8-20 cm long, 2-7 cm wide, 25- to 50-nerved; lower submersed leaves often decayed by fruiting time, lanceolate, often not folded, 19- to 25-nerved; both submersed leaf types obtuse to broadly acute, tapering to petioles 1-6 cm long. Floating leaves seldom lacking at flowering time, ovate to elliptic, 5-10 cm long, 3-7 cm wide, 25- to 45-nerved, obtuse or abruptly acute, cuneate or rounded at the base; petioles 5-15 cm long; stipules open and free of the petioles, 5-12 cm long, fibrous and persistent. Spikes cylindric, dense, 4-8 cm long in fruit; peduncles broadening upward, 5-20(30) cm long. Fruits greenish-brown to brown, obliquely obovoid, 4-5 mm long; dorsal keel prominent, the lateral keels less distinct; beak to 1 mm long. Jul--Aug. Quiet waters of streams and lakes; uncommon and local mainly in the e part; (Que. to B.C., s to AL, OK and CA).
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