222 COMMON CANADIAN WILD PLANTS. 



the petiole ; submerged leaves narrowly linear, or the upper 

 ones broad-linear, or, lance-oblong. Emersed flowers in 

 many-flowered spikes ; submersed flowers usually solitary. 

 Fruit either winged and 4-5-toothed, or wingless and entire. 



4. P. rufes'eens, Schrad. Stem simple. Submersed 

 leaves almost sessile, lanceolate and lance-oblong ; floating 

 leaves (often wanting) wedge-oblanceolate, narrowed into a 

 short petiole, 11-17-nerved. Spike dense, many-flowered. 

 Fruit obovate, lenticular, with acute margin, and pointed 

 with the long style. 



5. P. flu'itans, Roth. (P. lonchites, Tuckerm.) Stem 

 often branching below. Submersed leaves very long, lance- 

 olate and lance-linear, 7-15-nerved ; floating leaves lance- 

 oblong, or oblong-elliptical, long-petioled, 17-23- nerved. 

 Spike dense. Fruit obliquely obovate, 3-keeled when dry, 

 the middle one winged above. In streams mostly. 



6. P. amplifo'lius, Tuckerman. Submersed leaves large, 

 lanceolate or oval, acute at each end, recurved, wavy ; 

 stipules long and tapering. Floating leaves large, oblong 

 or lance-ovate, or slightly cordate, long-petioled, 30-50- 

 nerved. 



7. P. heterophyl'lus, Schreb. (P. gramineus, Fries.) 

 Stem slender, very much branched below. Submersed leaves 

 lanceolate or linear-lanceolate, acuminate or cuspidate, 3-7- 

 nerved, upper ones petioled, lower sessile ; floating leaves 

 variable, with short blunt points, 9-15-nerved. Stipules 

 obtuse. 



8. P. Ziz'ii, Mert. and Koch. (P. lucens, var. minor, 

 Nolte.) Much branched at the base. Upper leaves long- 

 petioled and sometimes emersed, the others nearly sessile, 

 all usually numerous, wavy and shining. Eesembling the 

 next species, but smaller. 



* * Leaves all submersed and similar, mostly sessile, membranaceous 

 and dilated. Stipules obtuse, becoming loose. 



9. P, lueens, L. Stem thick, branching. Leaves petioled 

 oval or lanceolate, mucronate, frequently shining. Fruit 

 roundish, comprised, Tjrith blunt edges, slightly keeled. 



