Northern Prairie Wildlife Research Center
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.
Previous Section -- Potamogeton friesii Rupr.
Return to Family -- Potamogetonaceae - The
Next Section -- Potamogeton illinoensis Morong
-- Illinois pondweed