26 NAJADACEAE. 



Stipules acuminate; fruiting spike 4-5 cm. long. P. americanus. 

 Stipules obtuse; fruiting spikes 2-3 cm. long. P. heterophyttus. 



Leaves alike, all submersed. 

 Leaves lanceolate to oblong. 



Not clasping at base. P. heterophyttus. 



Half clasping at base. 



Apex boat-shaped or hooded. P. praelongus. 



Apex acuminate, not hooded. P- richardsonii. 



Leaves linear. 



Stipules free from the base of the leaf. 



Leaves tape-like; spike cylindric; fruit large. P. zosterifolius. 



Leaves very narrow; spike not cylindric; fruit small. P. pusillus. 

 Stipules adnate to the base of the leaf. 



Leaves linear-lanceolate, 4-8 mm. wide, ciliate, 



many-nerved. P- robbinsii. 



Leaves linear-setaceous, 1 mm. wide, not ciliate, 



1-nerved -P. pectinatus. 



Potamogeton natans L. Floating leaves ovate or elliptical, somewhat 

 cordate at base, 5-8 cm. long; upper submerged leaves with a lanceolate blade, 

 the lower linear and grass-like; upper stipules long, acute; spike 3-5 cm. long, 

 emersed. 



Common in still ponds and lakes. 



Potamogeton epihydrus Raf. (P. nuttallii C. & S.) Stems simple or 

 branched, compressed, 60-120 cm. long; floating leaves oblong, obtuse or 

 acutish, each attenuate into a short petiole; submersed leaves numerous, linear, 

 thin, 5-7-nerved, with a coarse cellular reticulation between the inner nerves; 

 stipules short, obtuse; spikes 1-4 cm. long, on stout peduncles; fruit obovoid, 

 apiculate, 2-3 mm. long, 3-keeled when dry. 



Frequent in lakes and quiet rivers. 



Potamogeton amplifolius Tuckerm. Stem stout, simple or branched; 

 floating leaf-blades oblong-oval, acute, rounded at the base, 5-10 cm. long, 

 long-petioled ; submersed leaves mostly linear-lanceolate to lanceolate, the 

 uppermost frequently oval or oblong; stipules large, 5-10 cm. long, acute; 

 spike stout, dense, 2-4 cm. long, stout peduncled; fruit large, 4-5 mm. long, 

 with a broad beak. 



Rarely collected in our limits; Coupeville, Gardner; Whatcom County, 

 Washington, Suksdorf. 



Potamogeton americanus C. & S. (P. lonchitis Tuckerm.) Stems 

 slender, flaccid, branched, 50-100 cm. or more long; floating leaves narrowly 

 elliptic, pointed at each end, 5-10 cm. long, many-nerved, narrowed at base 

 into a petiole about as long; submersed leaves lanceolate; stipules narrow, 3—8 

 cm. long; spike dense, 2-4 cm. long, on rather stout peduncles; fruit about 3-4 

 mm. long. 



In ponds and streams, not common. 



Potamogeton heterophyllus Schreb. Floating leaves thin, obtuse, 9-15- 

 nerved, 3-5 cm. long; submersed leaves lanceolate or linear-lanceolate, 3-7- 

 nerved; stipules obtuse; fruit small, subglobose. 



Victoria, Macoun, and common eastward. 



Potamogeton praelongus Wulf. Leaves all submersed, numerous, oblong 

 or oblong-lanceolate, obtuse, half-clasping at base, 5-20 cm. long; peduncles 

 usually very long; spikes 2-5 cm. long, thick, loosely flowered; fruit sharply 

 keeled when dry, 4-5 mm. long. 



In lakes, rare in our limits. 



