446 NATADACEJE. (rOxmVEED FAMILY.) 



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

 leaves ; spikes slender, interrupted, on long filiform peduncles ; achenium obovate, 

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

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

 4' long. Spikes l'-2' long. 



2. P. pauciflorus, Pursh. Stem very slender, flattened, sparingly branched; 

 leaves scattered, thin, .'{-nerved, sessile; stipules free from the leaves, connate, 

 Bheathing; spikes Bhort-peduncled, 4 — 6-flowered, globose in fruit; achenium 

 round-obovate, short-pointed, keeled and sinuate-toothed on the back. — Shallow 

 ponds, Georgia, and northward. July and Aug. — Stem l°-2°long. Leaves 

 1'- 2' long. Peduncles £'- 1' long. 



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



3. 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 obliquely obovate, rounded 

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

 ward. July -Sept. — Stems 1°- 2° long. Leaves 6" -8" long. 



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

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

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

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

 compressed, rounded on the back, short-pointed. — Freshwater, Apalachicola, 

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



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

 petided and somewhat ccrriaceous. 



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

 ones varying from oblongdanccolatc to ovate, acute at each end, or obtuse or 

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

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

 thickened upward; spikes long, cylindrical, dense-flowered j achenium Bmooth, 

 1 -3-kceled 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-petioled (4'- 12') Leaves, more slender 

 peduncles, and rounded stipules and achenia. 



6. P. heterophyllus, Nchrehcr. Stem slender, branching ; floating leaves 

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

 s> -ile-, linear or Lanceolate ; stipules connate, 2-ribbed ; peduncles thickened np- 



. -pikes narrowly cylindrical ; achenium Bmooth, Blightly keeled on the back. 



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



2' long, [mmersed leave- i'-c' long. 

 T. P. hybridus, Michx. Small; stems very slender, branched; Boating 



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



