Aquatic and Wetland Vascular Plants of the Northern Great Plains
55. Potamogetonaceae, the Pondweed Family
1. Potamogeton L. -- Pondweed12. Potamogeton nodosus Poir. -- Longleaf pondweed
Stems subterete, 1-2 mm thick, simple or seldom branched, to 1.5 m long. Submersed leaves commonly deteriorating by fruiting time, linear-lanceolate to elliptic-lanceolate, 10-20(30) cm long, 1-2(3) cm wide, 7- to 15-nerved, acute to blunt-tipped, gradually tapering to petioles mostly (2)4-10 cm long. Floating leaves elliptic to oblong-elliptic, 5-13 cm long, (1.5)2-4.5 cm wide, 15- to 25-nerved, acute to nearly rounded at the tip, sometimes obtusely mucronate, acute to somewhat rounded at the base; petioles winged, mostly 2-3 mm wide, 5-20 cm long, usually longer than the blades; stipules free, those of the submersed leaves often decaying early, those of the floating leaves persistent, 3-10 cm long. Spikes dense, cylindric, 2-6 cm long; peduncles thicker than the stem, 3-15 cm long. Fruits reddish-brown to brown, obovoid, 2.7-4.3 mm long, the dorsal keel sharp, the lateral keels low. Jul--Aug. Shallow to rather deep water of streams, ponds and reservoirs; frequent in the s part, less common n; (Cosmopolitan).
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