NAIADACE.E. (fONDWEED FAMILY.) 471 



3. P. pusillus, L. Stem filiform, slightly compressed ; leaves narrowly 



linear, acute or acuminate, biglandular at the base ; stipules free ; peduncles 

 half as long as the leaves, 4 - 8-flowered ; achenia obliquely obovate, turgid, 

 rounded 011 the back; embryo hooked at the apex. Ponds, North Carolina, 

 and northward. 



- - Leaves lanceolate or cordate: stipules free, sheathing. 



4. P. perfoliatus, L. Stem terete, branching, very leafy ; leaves ovate, 

 cordate, clasping, obtuse, many-nerved, those at the branches and peduncles 

 opposite; spikes lateral and terminal, oblong, densely many-flowered, on 

 stout peduncles 2-3 times as long as the leaves ; achenium obliquelv obovate, 

 rounded ou the back, short-pointed. Fresh or brackish water, West Florida, 

 and northward. July - Sept. Stems 1 - 2 long. Leaves 6" - 8" long. 



5. P. lucens, L. Stem branching ; leaves short-petioled, oblong-lanceo- 

 late, mucronate-acute ; stipules long, connate ; peduncles stout, longer than 

 the leaves ; acheuia roundish, compressed, slightly 3-keeled. Lakes and 

 ponds, Florida (?), and northward. 



6. P. Zizii, Mert. & Koch. ? Stems sparingly branched ; leaves lanceo- 

 late, acute, contracted and sessile at the base, pellucid, 5-9-nerved, wavv on 

 the margins; stipules (white) connate, rounded on the back; spikes cylindri- 

 cal, many -flowered, on stout peduncles shorter than the leaves; achenium 

 (immature) oval, compressed, rounded on the back, short-pointed. Fresh 

 water, Apalachicola, Florida. August. Stems 2 -3 long. Leaves 2' -3' 

 long. 



* * Leaves of two forms; the immersed ones thin and pellucid, the floating ones 

 long-petioled and somewhat coriaceous. 



7. P. amplifolius, Tuck. Stem simple, floating ; leaves (mostly absent) 

 large, oblong or oval-lanceolate, acutish, long-petioled; the submerged ones 

 lanceolate, undulate; stipules very long, pointed; peduncles stout, fruit 

 obliquely obovate, bluntly keeled. Ponds on the mountains of Georgia, and 

 northward. 



8. P. Pennsylvanicus, Cham. Stem slender, branching; floating 

 leaves opposite, thin, elliptical or oblong-linear, on filiform petioles; immersed 

 leaves long, sessile, linear or lanceolate ; stipules connate, 2-ribbed ; peduncles 

 thickened upward; spikes narrowly cylindrical; achenium smooth, slightly 

 keeled on the back. Shallow ponds, North Carolina, and northward. July. 

 Floating leaves l'-2' long. Immersed leaves 4' -6' long. 



9. P. hybl'idus, Michx. Small ; stems very slender, branched ; float- 

 ing leaves lanceolate or elliptical, commonly acute at each end, shining and 

 strongly impressed-nerved, longer than the filiform petioles; immersed leaves 

 filiform, scattered ; spikes oval or oblong, short-peduncled ; achenium nearly 

 circular, concave on the sides, rugose or tuberculate, and 1 - 3-ridged on the 

 back; embryo coiled. Shallow ponds. June -August. Floating leaves 

 6" - 8" long, commonly 5-nerved. 



