Northern Prairie Wildlife Research Center
Aquatic and Wetland Vascular Plants of the Northern Great Plains
55. Potamogetonaceae, the Pondweed Family
1. Potamogeton L. -- Pondweed
10. 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
See discussion under the preceding.
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