I 



NAIADACK.t. (I'ONDWEED FA.MII.V.) 5GI 



near the base of the stem) thirlrr, plane, oval or nhlonrj with a rounded base, 

 or si»atulateoblong, on longer petioles; stipules rather sliort and obtuse; pe- 

 duncles thicker than the stem ; fruit witii a rounded back and angular face, 

 pointed, distinctly 3-keeled when fresh, sharply so when dry ; nutlet with two 

 deep dorsal furrows, and a sinus below the angle in front ; siiles Hat ; embryo 

 circularly nnuli incurved above. — Ponds, Vt. to Ga. and Mo. July, Aug. 



11. P. amplifolius, rnckerm. Stems simple, of very variable leiigih ; 

 Jlodtiivj leaves (sometimes wanting) large, obluiKj or lance-ovate, sometimes 

 sligbtly cordate at base, abruptly acutish, 30- 50-nerved, on rather lunfj jicti- 

 oles ; submersed leaves often very large (reaching 7' l)y 2'), lanceolate or oval, 

 acute at each end, usualli/ much recurved, undulate, mostly on short petioles; 

 stipules veri/ long and tapering to a point, soon becoming loose ; peduncles 

 thickened upward, in deep water much elongated; fruit very large (over 2" 

 long), rather obliquely obovate, 3-keeled, with a broad stout beak; nutlet 

 slightly impressed on the sides ; upper part of the embryo curved into a ring. 

 — Ponds and rivers, X. Eng. to N. J., west to ]Minu, and Kan. Aug., Sept. 



12. P, Illino6nsis, Morong. Stem stout, branching towards the sum- 

 mit; floating leaves opposite, oval or ovate (2-5' long by 1^-2' broad), 19 - 

 25-nerved, rounded or subcordate at base, with a short blunt point at apex, on 

 short petioles ; submersed leaves rather few, oblong-elliptical, acute at each end, 

 usualli/ ample (largest 8' by 1^') ; stipules coarse, obtuse, strongly bicarinate 

 (2' long) ; peduncles often clustered at the summit (2-4' long), thickening 

 upward; //-h/^ round ish-obovate {\%-2" long), 3-keeled on the back, middle 

 keel prominent ; nutlet flattened and slightly impressed on the sides, obtuse 

 or pointed at base ; apex of embryo directed transversely inward. — Streams 

 and ditclies, western N. Y. to 111., Iowa, and Minn. Very near the last. 



13. P. heterophyilus, Schreb. Stem slender, very branching below; 

 floating leaves mostly thin, variable, but with a short blunt point, 9 - 15-nerved, 

 usually 1 - 2' long and G - 9" wide ; submersed ones usually lanceolate or linear- 

 lanceolate, acuminate or cuspidate, narrowed toward the base, about 7-nerved 

 on the stem and 3-nervcd on tlie branches; upper ones petioled, lower sessile ; 

 stipules obtuse, loo.sc; peduncles somewhat thickened upward; fruit small, 

 roundish, compres.scd, scarcely keeled ; embryo annular above. (P. gramineus. 

 Fries.) — Still or flowing water, common* Varies exceedingly in its sub- 

 mersed leaves, peduncles, etc.; the var. gramixifolius (Fries), growing in 

 rapid streams, with stems much elongated and less brauclicd, and the flaccid 

 submersed leaves 2-7' long by 2- 10" wide. 



Var. (?) myriophyllus, Kobbins. Sending up from runnuig rootstocks 

 many short repeatedly dichotomous and densely leafy stems; fertile stems 

 very slender; floating leaves small, delicate, lance-oblong, on long filiform 

 petioles; submersed stem-leaves larger, early perishing; those of the branches 

 (deep-green) linear-oblanceolate, very small {\-V long), acute, sometimes 

 minutely serrulate; spike slender, loosely-flowered, much shorter than the 

 thickened peduncle. — Apponaug JL'ond, R. I., without fruit. 



13*. P. Zizii, Mert. & Koch. Resembling P. lucens, but smaller, much 

 branched at base; upper leaves coriaceous or subcoriaccous, long-petiolcd and 

 sometimes emersed, the others subsessile, all usually numerous, undulate and 

 shining ; peduncle elongated. (P. lucens, var. minor, Nolle. Also P. gramin- 

 eus, var. (?) spathulaeformis, A'o66;>K<j ; P. spathseformis, Tuckerm. ; "P. vari- 



36 



