446 NAIADACK-E. (I'ONDWKI I) FAMILY.) 



the branches ; stipules small, united with the long and sheathing base of the 

 leaves ; spikes slender, interrupted, on long filiform pcduneles ; aclicnium ohovate, 

 smooth, slightly compressed, keeled on the back. — Fresh or brackish water, 

 West Florida, and iiortliward. June - Aug. — Stems 2° - 3° long. Leaves li' - 

 4' long. Spikes 1'- 2' long. 



2. P. pauciflorus, rur>h. Stem very slender, flattened, sparingly branched; 

 leaves scattered, thin, 3-ncrvcd, sessile; stipules free fiom the leaves, connate, 

 sheathing; spikes short-pcdunclcd^ 4 - 6-flo\vercd, globose in fruit; aclicnium 

 round-obovatc, short-pointed, keeled and sinuate-toothed on the back. — Sliallow 

 ponds, Georgia, and northward. July and Aug. — Stem l°-2°long. l.ca\».j 

 1 ' - 2' long. Teduneles ^' - 1 ' long. 



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



3. P. perfoliatUS, L. Stem terete, branching, A'cry leafy ; leaves ovate, 

 cordate, clasping, ol)tusc, many-nerved, those at tiie branches and i)cdunclcK 

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

 peduncles 2-3 times as long as the leaves ; achenium obliquely obovatc, rounded 

 on the back, short-pointed. — Fresh or brackish water. West Florida, and north- 

 ward. July - Sept. — Stems l°-2° long. Leaves 6"- 8" Jong. 



4. P. lucens, L. 1 Stems sparingly branched ; leaves lanceolate, acute, 

 contracted and sessile at the base, pellucid, 5-9-ncrved, wavy on the margins; 

 stipules (white) connate, rounded on the back ; spikes cylindrical, many-flow- 

 ered, on stout peduncles shorter than the leaves ; achenium (immature) oval, 

 compressed, rounded on the back, short-pointed. — Fresh water, Apalaehicola, 

 Florida. Aug. — Stems 2° -3° long. Leaves 2'-3' long, equalling the spikes. 



* * Leaves of two farms ; the immersed ones thin and ptllucid, the floatimj ones loug- 

 petioled and somewhat coriaceous. 



5. P. fluitans, Roth. Stem simple ; leaves many-nerved ; the floating 

 ones varying from oblong-lanccolatc to ovate, acute at each end, or obtuse or 

 cordate at the base ; the others large, oblong, gradually or abruptly short- 

 pctiolcd, undulate ; stipules connate and keeled on the back ; peduncles stout, 

 thickened upward; spikes long, cylindrical, dense-flowered ; achenium smooth, 

 1 - 3-keeled on the back. — Fresh-water ponds and streams, Florida, and north- 

 ward. June - Aug. — Leaves 2' - 9' long. 



P. KATANS, L. probably occurs within our limits, but I have not seen 

 specimens. It may be known by longer-pet ioled (4'- 12') leaves, more slender 

 peduncles, and rounded stipules and achenia. 



C. P. heterophyllus, Schreber. Stem slender, branching ; floating leaves 

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

 sessile, linear or lanceolate ; stipules connate, 2-ribbed; peduncles thickened up- 

 ward ; spikes narrowly cylindrical ; achenium smooth, slightly keeled on the back. 

 — Shallow ponds. North Carolina, and northward. July. — Floating leaves 1'- 

 2' long. •Immersed leaves 4'-G' long. 



7. P. hybridus, Michx. Small ; stems very slender, branched ; floating 

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



