196 



NAIADACE^E. Potamorjeton. 



ate into a very broad short petiole ; stipules broad, usually acuminate, -|- to 1 inch 

 loni^' or more ; submerged leaves as large as the floating ones, sessile or nearly so, 

 mostly alternate, narrowly oblong-lanceolate (3 to 6 lines broad), obtuse or acute, 

 the midrib bordered by rows of narrow longitudinal cells : spikes 1 or 2 inches long, 

 rather slender, on stout often elongated peduncles: fruit round-obovate, IJ- lines 

 long, compressed, acutely margined, beaked by the rather long style : nutlet pitted 

 on each side : embryo nearly circular. — Reichenb. 1. c, t. 32. 



In streams or ponds ; collected only in Silver Valle}', Alpine County {Brewer) ; found also in 

 Montana and Colorado (Richardson, Jones), and common in the Atlantic States, from New Eng- 

 land to Texas, as well as in Europe. 



4. P. lonchites, Tuckerman. Stem rather slender, branching : floating leaves 

 thickish, 11 -23-nerved, long-elliptical to oblong-lanceolate, usually 2 to 4 inches 

 lon*^ by 9 to 15 lines wide, acute or acutish, rather abruptly narrowed into a petiole 

 usually longer than the blade ; submerged leaves thinner, mostly linear-lanceolate, 

 3 to 12 inches long by 2 to 12 lines broad, more attenuate at base, the lower sessile ; 

 stipules large : spikes dense, 1 or 2 inches long, on stout peduncles : fruit obliipiely 

 obovate, H or nearly 2 lines long, carinate, acute: nutlet somewhat 3-keeled, the 

 sides scarcely impressed : cotyledon incurved above the base of the embryo. — 

 Amer. Journ. Sci. 2 ser. vi. 226 and vii. 350. P. montanum, Presl, Eel. Htenk. 

 i. 85 and 351? P. natans, \av. Jluitans, Benth. PI. Hartw. 341. 



In streams or rarely in ponds ; near Santa Cruz (Harhvcg, n. 201 7) ; Washington Territory 

 {Lyall) ; Humboldt Pass, Nevada ( Watson) ; and in the Atlantic States from British America to 

 Mexico.' Presl's description of the Monterey plant of Haenke leaves its identity very uncertain. 



5. P. amplifolius, Tuckerman. Stems often stout, simple : floating leaves 

 (sometimes wanting) 30 - 50-nerved, elliptic to oblong-lanceolate, acute, mostly 

 rounded or slightly cordate at base, 2 to 4 inches long, on stout petioles about 

 equalling the blade ; stipules large and conspicuous ; submerged leaves often very large 

 (4 to 7 inches long by 2 inches wide or more), mostly falcate and somewhat undu- 

 late, acute, attenuate to a usually short petiole : spike thick and often dense, 1 to 

 3 inches long, on a very stout peduncle : fruit large (over 2 lines long), 3-keeled, 

 with a broad'stout beak : sides of the nutlet not pitted : embryo slender, the coty- 

 ledon incurved. — Amer. Journ. Sci. 2 ser. vi. 225 and vii. 349. 



In ponds and streams ; Sierra County (Lc7nmon) ; Oregon (HaU) ; common in the Atlantic 

 States from New England to Kansas and New Mexico. 



6. P. gramineus, Linn. Stems very slender, branching : floating leaves rather 

 thin, 9 - 15-ncrved, small (usually an inch or two long by 6 to 9 lines wide), oblong- 

 elliptic, acutish, rounded or cuneate at base, on slender petioles mostly equalling or 

 exceeding the blade ; stipules broad, obtuse, an inch long or less ; submerged leaves 

 linear-lanceolate, variable in length, more commonly short (1 or 2 inches long by 1 

 to 3 lines broad, var. heterophj/llns, Fries), acute or acuminate, narrowed at base : 

 spikes about an inch long, rather loose, on stout often elongated peduncles : fruit 

 round-obovate, a line long, acute, scarcely keeled: embryo stout; cotyledon in- 

 curved. — P. heterophyllus, Schreb. ; Reichenb. 1. c. 24, t. 41-43. 



In still or flowing water ; Soda Spring, near Mono Pass {Brewer) ; Kuby Lake, Nevada ( Wat- 

 son) ; Yellowstone Basin, Montana {Richardson) ; common eastward, from Canada to North Caro- 

 lina, and also European. 



* * Leaves all submerged and uniform, thin and dilated {lanceolate to oval), 

 numerous, mostly sessile: spikes dense, on stout peduncles. 



7. P. lucens, Linn. Stem stout, branching : leaves mostly thickish, usually 

 large (2 to 6 inches long), oblong-lanceolate or oblanceolate, rather abruptly acute or 

 acuminate, mucronate, often undulate-serrate, narrowed at base to a short petiole or 

 subsessile ; stipules large, often spreading : spikes 1 or 2 inches long ; peduncles 

 often elongated : fruit rounded, 1| lines long, acute, slightly keeled : cotyledon in- 



