Aquatic and Wetland Vascular Plants of the Northern Great Plains
55. Potamogetonaceae, the Pondweed Family
1. Potamogeton L. -- Pondweed10. Potamogeton illinoensis Morong -- Illinois pondweed
Stems subterete, (1)1.5-5 mm thick, simple or branched, to 2 m long. Submersed leaves elliptic or oblong-elliptic to lanceolate or linear-lanceolate, sometimes somewhat arcuate, 5-20 cm long, (1)1.5-4 cm wide, mostly 9- to 17(19)-nerved, acute to mucronate, tapered to the subsessile or petioled base, the petioles up to 2-4 cm long. Floating leaves often lacking, oblong-elliptic or ovate-elliptic to broadly elliptic, 4-14(19) cm long, 2-7 cm wide, 13- to 29-nerved, obtuse to bluntly mucronate at the tip, rounded to cuneate at the base; petioles 2-9 cm long, shorter than the blades; stipules free, persistent, mostly 2-8 cm long. Spikes dense, cylindric, 2-6 cm long; peduncles usually thicker than the stem, 4-20(30) cm long. Fruits olive-green or gray-green, obliquely obovoid, 2.7-3.5 mm long, dorsal and lateral keels prominent. Jun--Sep. Shallow to fairly deep water of sandy lakes and ponds; common in the NE Sandhills, otherwise widely scattered in SD; (N.S. to Ont. and B.C. s to FL, KS, CA and into Mex.).
See discussion under the preceding.
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