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Aquatic and Wetland Vascular Plants of the Northern Great Plains

55. Potamogetonaceae, the Pondweed Family

1. Potamogeton L. -- Pondweed

9. Potamogeton gramineus L. -- Variable pondweed

Stems subterete, 0.5-1 mm thick, usually freely branched, to 8 dm long. Submersed leaves linear to linear-lanceolate or broadly lanceolate, sometimes oblanceolate, 3-9 cm long, 3-15 mm wide, 3- to 7(9)-nerved, acute to acuminate, tapered to the sessile base. Floating leaves rarely absent, elliptic or oblong-elliptic, 2-9 cm long, 1-3.5 cm wide, 11- to 19-nerved, obtuse or abruptly acute at the tip, rounded to cuneate at the base; petioles 2-10(15) cm long, shorter than to exceeding the length of the blade; stipules free, persistent, mostly 0.5-4 cm long. Spikes dense, cylindric, 1.5-3.5 cm long; peduncles stout, usually broadening upward, 2-10(20) cm long. Fruits dull green, obliquely obovoid, 1.7-2.8 mm long, dorsal keel sharp, lateral keels obscure. Jun--Aug. Shallow, usually standing water of ponds, lakes, marshes and ditches; frequent in n and c ND, ne SD and the NE Sand Hills, otherwise occasional; (Circumboreal, in N.Amer. s to NY, IA, NE and CA).

Apparent hybrids between P. gramineus and the following species are frequently observed among collections from the Nebraska Sand Hills where they often grow together. The hybrids are typically intermediate between the parents in morphology, but may be mistaken for extremes of either parent. Flowers should be checked for abortive pollen grains to confirm a suspected hybrid.
GIF- Species Photo/Drawing
Potamogeton gramineus.
GIF- Distribution Map

Map key

Previous Section -- Potamogeton friesii Rupr.
Return to Family -- Potamogetonaceae - The Pondweed Family
Next Section -- Potamogeton illinoensis Morong -- Illinois pondweed

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