Aquatic and Wetland Vascular Plants of the Northern Great Plains

Potamogeton L. -- Pondweed

Submersed or floating-leaved, rhizomatous aquatics, perennial from the rhizomes or tubers or by budding from the lower nodes, sometimes reproducing and overwintering by free-floating winter buds. Stems elongate, flexuous, anchored by roots and rhizomes. Leaves alternate, becoming opposite upward in some spp., simple; stipules present, fused to each other along one or both margins or adnate to the leaf blade in some linear-leaved spp., forming an open or closed sheath around the stem, fibrous or membranous, often rapidly deteriorating. Submersed leaves filiform to lanceolate, thin and often flexuous, usually sessile. Floating leaves produced in some spp., basically elliptic or oblong in outline, petioled, rather leathery with a waxy upper surface. Winter buds produced in the leaf axils of some spp., these consisting of tightly compressed apices bound by reduced leaves. Inflorescences of axillary or terminal spikes bearing few to many minute whorled flowers; peduncles stout to filamentous, usually lifting the spike above the water surface at anthesis, often recurved with age. Flowers perfect, regular; perianth of 4 sepaloid bracts (these considered enlargements of the staminal connectives by some authors); stamens 4, each inserted on the claw of a perianth bract; carpels 4, separate, each maturing into a strongly to weakly beaked, nutlet-like fruit.

References:

Fernald, M. L.  1932.  The linear-leaved North American species of 
     Potamogeton section Axillares.  Mem. Amer. Acad. 	
     Arts 17:1-183. 

Haynes, R. R.  1974.  A revision of North American Potamogeton 	
     subsection Pusilli (Potamogetonaceae).  Rhodora 76:564-649. 

Larson, G. E.  1976.  The Potamogetonaceae in North Dakota.  Prairie 	
     Natur. 8:1-18. 

Ogden, E. C.  1943.  The broad-leaved species of Potamogeton of North 	
     America north of Mexico.  Rhodora 45:57-105, 119-163, 171-214. 

Reznicek, A. A. and R. S. W. Bobbette.  1976.  The taxonomy of 	
     Potamogeton subsection Hybridi in North America.  Rhodora 
     78:650-673. 

St. John, H.  1916.  A revision of the North American species of 
     Potamogeton of the section Coleophylli.  Rhodora 18:121-138.

Lead	Characteristic	Go To
1	Stipules adnate to the leaf blades for a distance of 10 mm or more, the free portion projecting as a ligule; floating leaves absent.	Lead 2
1	Stipules free of the blade or adnate for a distance of less than 10 mm, often early deteriorating; floating leaves present or absent.	Lead 4
2	Stipular sheaths of the main stem inflated 2-5X the thickness of the stem; floral whorls 5-12 per spike.	P. vaginatus
2	Stipular sheaths of the main stem about as wide as the stem; floral whorls 2-6 per spike.	Lead 3
3	Stems dichotomously branched from the base, mostly unbranched above; fruits olivaceous, 2-3 mm long, the beak flat, inconspicuous.	P. filiformis
3	Stems dichotomously branched above; fruits yellowish to brown, 3-4 mm long, apiculate, with a beak usually 0.3-0.5 mm long.	P. pectinatus
4	Submersed leaves linear, 6 mm or less wide (sometimes wider in P. epihydrus), mostly 20X or more longer than wide.	Lead 5
4	Submersed leaves linear-lanceolate, lanceolate, oblong or ovate, broader in proportion to the length.	Lead 12
5	Stipules adnate to submersed leaf blades for mostly 1-4 mm; embryo coil plainly visible through the papery thin walls of the fruit; small elliptic floating leaves usually present, 5-40 mm long.	P. diversifolius
5	Stipules free of the leaf blades; fruit walls firm, the embryo coil obscured by the walls of the fruit; floating leaves, if present, mostly larger.	Lead 6
6	Leaves dimorphic, both floating and submersed leaves produced.	Lead 7
6	Leaves all alike, all submersed.	Lead 8
7	Submersed leaves reduced to phyllodes 1-2 mm wide, these often absent with age; floating leaves rounded to cordate at the base.	P. natans
7	Submersed leaves ribbonlike, mostly 3-6(10) mm wide, with a cellular-reticulate strip on each side of the midvein forming a conspicuous median band 1-2 mm wide; floating leaves tapered to the petiole.	P. epihydrus
8	Leaves with many (15-35) fine nerves; mature fruits 4-4.5 mm long.	P. zosteriformis
8	Leaves 3- to 7(9)-nerved; mature fruits 1.5-3.6 mm long.	Lead 9
9	Fruits with an undulate to dentate dorsal ridge or keel; glands rarely present at the base of the stipules.	P. foliosus
9	Fruits dorsally smooth and rounded; glands usually present at the base of the stipules.	Lead 10
10	Stipules whitish, fibrous, the oldest often shredding into fibers; peduncles mostly clavate; indurate winter buds often present.	Lead 11
10	Stipules tan to brownish-green, delicate, usually decomposing with age; peduncles filiform to cylindric; winter buds seldom present.	P. pusillus
11	Leaf tips acute, rarely obtuse; leaves 3- to 5(7)-nerved, 0.6-2 mm wide; peduncles mostly terete; stems mostly terete.	P. strictifolius
11	Leaf tips rounded to apiculate; leaves 5- to 7(9)-nerved, 1.2-3.2 mm wide; peduncles compressed; stems compressed.	P. friesii
12	Leaves all submersed, sessile, weakly to strongly clasping at the base, often undulate-crisped.	Lead 13
12	Floating leaves commonly present by flowering time, occasionally lacking; submersed leaves sessile or petiolate, not clasping the stem; flat to falcate, not undulate-crisped.	Lead 15
13	Leaf margins finely serrate; fruit beak 2-3 mm long; indurate winter buds commonly produced in upper axils.	P. crispus
13	Leaf margins entire; fruit beak 1.5 mm or less long; winter buds lacking.	Lead 14
14	Stems whitish; leaves 10-25 cm long; peduncles over 10 cm long; fruits 4-5 mm long.	P. praelongus
14	Stems brownish to yellowish-green; leaves less than 10 cm long; peduncles 2-10 cm long; fruits 2.5-3.5 mm long.	P. richardsonii
15	Upper submersed leaves falcate-folded, 25- to 50-nerved; mature fruits 4-5 mm long.	P. amplifolius
15	Upper submersed leaves more or less symmetrical and not folded, 3- to 17(19)-nerved; mature fruits 1.7-4 mm long.	Lead 16
16	Fruits tawny-olive; floating leaves often lacking, thin and delicate, the blade tapering indistinctly into a short petiole; submersed foliage reddish-tinged.	P. alpinus
16	Fruits brown, reddish-brown or greenish; floating leaves leathery, the blades distinct from the petioles; submersed foliage dark green to brownish-green.	Lead 17
17	Submersed leaves commonly disintegrating by fruiting time, tapering to petioles (2)4 cm long or much longer, acute to blunt-tipped; mature fruits brownish to reddish-brown, 3-4 mm long.	P. nodosus
17	Submersed leaves usually persistent, sessile or tapering to petioles up to 4 cm long, acute to abruptly acuminate or apiculate; mature fruits green or olive, 1.7-3.5 mm long.	Lead 18
18	Stems usually freely branched, 0.5-1 mm thick; submersed leaves 3-10(15) mm wide, 3- to 7(9)-nerved; floating leaf blades 2-9 cm long, 1-3.5 cm wide; fruiting spikes 1.5-3.5 cm long; fruits 1.7-2.8 mm long, the lateral keels obscure.	P. gramineus
18	Stems simple or once-branched, 1-5 mm thick; submersed leaves (1)1.5-4 cm wide, 9- to 17(19)-nerved; floating leaf blades 4-14(19) cm long, 2-7 cm wide; fruiting spikes 2-6 cm long; fruits 2.7-3.5 mm long, the lateral keels strong.	P. illinoensis