Aquatic and Wetland Vascular Plants of the Northern Great Plains
55. Potamogetonaceae, the Pondweed Family
1. Potamogeton L. -- Pondweed7. Potamogeton foliosus Raf. -- Leafy pondweed
Stems compressed, mostly 0.5-1 mm wide, freely branched, to 8 dm long. Leaves all submersed, linear, 1.3-8.2 cm long, 0.3-2.3 mm wide, 1- to 3(5)-nerved, acute to apiculate at the tip, tapered to the sessile base; stipules free, greenish to brown, mostly 0.5-2 cm long, membranous or fibrous, eventually deteriorating; glands rarely present at the base of the stipules. Winter buds uncommon, lateral, 1-2 cm long. Spikes capitate to short-cylindric, 1.5-7 mm long; floral whorls 1 or 2, the whorls 0.6-1.2 mm apart when 2; peduncles usually clavate, recurved, 3-10 mm long. Fruits olive to greenish-brown, obliquely obovoid, 1.4-2.7 mm long; dorsal keel ridged or winged, with an undulate to dentate margin 0.1-0.4 mm high; sides rounded to centrally depressed. Jun--Aug. Shallow water of rivers, streams, lakes and ponds; common except in the nw portion of the region; (Newf. to B.C., s throughout most of the U.S. and into Mex. and C.Amer.; also HI and W. Indies).
Two varieties of P. foliosus occur in the region. In the w part, var. fibrillosus (Fern.) Haynes enters the region; we have collections from Pennington Co., SD, Rosebud Co., MT and Albany Co., WY. This variety is distinguished as follows: Spikes mostly interrupted; fruit pale green, 1.4-1.7 mm long, 1.1-1.2 mm wide; keel mostly less than 0.2 mm high; beak 0.2 mm long or less; stipule veins persistent as long fibers; basal glands common, to 0.5 mm in diameter.
The great majority of Great Plains plants are var. foliosus which
differs as follows: Spikes rarely interrupted; fruit olive to
greenish-brown, 1.5-2.7 mm long, 1.2-2.2 mm wide; keel mostly 0.2 mm
high or more; beak 0.2-0.6 mm long; stipule veins decaying;
basal glands rare, to 0.3 mm in diameter.
Previous Section -- Potamogeton filiformis Pers. -- Slender pondweed
Return to Family -- Potamogetonaceae - The Pondweed Family
Next Section -- Potamogeton friesii Rupr.
