POTAUOOETOK NAIABACE^ 676 



Sterna simple or branched, 1-2 feet high, somewhat compressed : floating 

 leaves often wanting, rather thin, 11-17-nerved, narrowly oblong-elliptic 

 or oblanceolate, 2-1 inches long, acatish, attenuate into a very broad short 

 petiole ; submerged leaves as large as the floating ones, sessile or nearly so, 

 mostly attenuate, narrowly oblong-lanceolate, 3-12 inches long, 3-6 lines 

 wide: stipules broad, usually acuminate, 6-12 lines long or more : spikes 

 1-2 inches long, rather slender, on stout often elongated peduncles : fruit 

 round-obovate, IX lines long, compressed acutely margined, beaked by the 

 'rather long style: nutlets pitted on both sides: embryo nearly circular, 

 in alpine ponds, Brit. Columbia to Galifornia and the Eastern States, also 

 in Europe. 



P. lonohites Tuckerman Am. Journ. Sci. (II) vi, 226. Stems rather 

 slender, branching, terete, 3-6 feet long : floating leaves thickish, 11-23- 

 nerved, long-elliptical to oblong-lanceolate, usually 2-4 inches long, 9-15 

 lines wide, acute or acutish, rather abruptly narrowed into a petiole, usu- 

 ally longer than the blade ; submersed leaves thinner, mostly linear-lance- 

 olate, 3-12 inches long, 2-12 lines wide, attenuate at base, the lower sessile : 

 stipules 1-4 inches long : spikes dense, 1-2 inches long, On stout peduncles; 

 fruit obliquely obovate, 1-2 lines long, carinate, acute: nutlets somewhat 

 3-keeled_, the sides scarcely impressed : cotyledons incurved above the base 

 of the slightly incurved embryo. In ponds and slow streams, Washington 

 to California and the Eastern States. 



P. beterophyllns Schreb. Special Fl. Lip. xxi, 1771. Stems very 

 slender, branching : floating leaves rather thin, 9-15-nerved, oblong-ellip- 

 tic, acutish, 1-2 inches long, rounded or cuneate at base, on slender peti- 

 oles mostly as long or longer than the blade : stipules broad, obtuse, about 

 an inch long : submersed leaves linear-lanceolate, 1-2 inches long, 1-3 lines 

 wide, 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, incurved. In different 

 forms throughout most parts of North America : also in Eerope. 



* * Leaves all submerged and uniform, thin and dilated, numer- 

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



P. prtelongus Wulf. in Bcem. Arch, iii, 331. Stems stout, elonga- 

 ted, branching and flexuous above, usually growing in deep water, some- 

 times 8 feet long : leaves often lanceolate, 2-10 inches long, 6-12 linesi 

 wide, obtuse and somewhat cucullate at the apex, rounded and clasping at 

 base, undulate-serrate: stipules whit6 and conspicuous, 6-12 lines long: 

 peduncles often much elongated ; fruit semicircular, 2 lines long, acutely 

 keded, prominently Ijeaked: embryo slender, the cotyledons pointing to 

 the base of the radicle. In deep water, Brit. Columbia to California and 

 the Eastern States. 



P. ^erfoUatus. L. Sp. 126. Stemsslender, not flexuous, 2-4 feet high, 

 branchmg : leaves broadly cordate to cordate-lanceolate, 6-18 inches long, 

 obtuse to acute, clasping at base : stipules small and not persistent : spikes 

 8-12 lines long, often flowering and fruiting under water : fruit obliquely 

 obovoid, nearly 1}^ lines long, obtusely keeled, beaked b;^ the short slender 

 style : embryo slightly incurved or with the apex pointing directly toward 

 the base. In streams and ponds, California to Brit. Columbia and across 

 the continent. 



Var. Bichardsonii A. Bennett Britten's Journ. Bot. xxvii, 25. 

 Leaves 1-5 inches long, 4-^ lines wide at the broadened amplexicaul base, 

 Qften curved inward at the apex, 13-23-nerved : fruit about 2 lines long, 

 1^ lines thick. In streams and ponds, Oregon to California and Delaware. 



P. zostertefoUns Schum. Enum. Fl, Saell. 50. Stems much flattened. 



