295 NAIADACD.E. Potamoijdon. 



ate into a very broarl short petiole ; stipules broad, usually acumitiate, i to 1 inch 

 long or more ; submerged leaves as large as the lloaliiig ones, sessile or nearly so, 

 mostly alternate, narrowly oblongdaneeolate (."i to G lines hnjad), obtuse or acute, 

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

 rather slender, on stout often elongated peduncles: IVuit round-obovate, li lines 

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

 on each side: embryo nearly circular. — Keichenb. 1. c, t. '3'2. 



Ill streams or j)on(ls ; collected only in Silver Valley, Alpine ("ounty (Brewer) ; fouml also in 

 Montana and Colorado (Rickardson, Junes), and coiniiion 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, 1 1 - I'.i-nerved, long-elliptical to oblongdanceolate, usually 2 to 4 inches 

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

 usually longer than the blade ; submergeil 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, oarinate, acute: nutlet somewhat 3-keeled, the 

 sides scarcely im[)ressed : cotyledon incurved above the base of the embryo. — 

 Amer. Journ. Hci. 2 ser. vi. 220 ami vii. 350. P. viontdnuui^ I'resl, IJel. Iheiik. 

 i. 85 and 351 ] P. natuus, yav. Jlnifdiis, l>enth. IM. llartw. 341. 



In streams or rarely in ponds; near Santa Cruz (Iltirfiue;/, n. •2017); Wasliington Territory 

 (Lyall); Humboldt Tass, Nevada {Wdlson); and in tlie Atlantic States from Hiitisli Amciica to 

 Mexico. Picsl's description of the Monterey plant of Ilaenke 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 conlate at base, 2 to 4 inches long, on stout jietioles about 

 equalling the blaile; stipules large ami conspicuous; submerged leaves often very large 

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

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

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

 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. 341). 



In i)onds and streams; Sierra County (Le7nmr)n) ; Orcf^on {IlalD; common in tlie Atlantic. 

 States fiom New England to Kansas and New Mexico. 



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

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

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

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

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

 round-obovate, a line long, acute, scarcely keeled : (;mbryo st(nit ; cotyledon in- 

 curved. — P. heteropIiijUns, Schrel). ; lieichenb. 1. c. 24, t. 41-43. 



In still or flowing water ; Soda Spring, near Mono Pass (/?/T»rr) ; Hid'y biil<<'. Nevada ( //'<//■ 

 so)i) ; Yellowstone Basin, Montana {Uirliurdson) ; cDiiimon eastward, fVuiii Canada to North Caio- 

 liiia, and also European. 



* * Leaves all suhmerf/ed and uniform, thin and dilated (lanrenlate to ocal), 

 minieroHS, vwstly sessile: spikes dense, on stout peduncles. 



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

 large (2 to G inciies long), oblong-lanceolate or oblanceolate, rather abruptly acute or 

 acuminate, mucronate, often undulate-serrate, narrowed at base to a short i)etiole or 

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

 often elongatetl : fruit rounded, \}f lines long, acute, slightly keeled : cotyledon in- 



