Northern Prairie Wildlife Research Center
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 |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/resource/plants/vascplnt/genpotam.htm
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