446 NAIADACEH, (PONDWEED 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 1'- 2' long. 
2. P. pauciflorus, Pursh. Stem very slender, flattened, sparingly branched; 
leaves scattered, thin, 3-nerved, sessile; stipules free from the leaves, connate, 
sheathing; spikes short-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 1°-2° long. Leaves 
l'-2'long. Peduncles j/- 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; acheninm (immature) oval, 
compressed, rounded on the back, short-pointed. — Fresh water, A 
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- 
petioled and somewhat coriaceous. : 
5. P. fluitans, Roth. Stem simple; leaves many-nerved; the floating 
ones varying from oblong-lanceolate to ovate, acute at each end, or obtuse x 
cordate at the base; the others large, oblong, gradually or abruptly a 
petioled, undulate ; stipules connate and keeled on the back ; peduncles stoub 
thickened upward ; spikes long, cylindrical, dense-flowered ; achenium 
1 ~3-keeled on the back. — Fresh-water ponds and streams, Florida, and north- 
ward. June- Aug. — Leaves 9! — 9! long. : 
P. xaTANs, L. probably occurs within our limits, but I have not se 
specimens. It may be known by longer-petioled (4'— 12!) leaves, more ia 
peduncles, and rounded stipules and achenia. ps 1 
_ 6. P. heterophyllus, Schreber. Stem slender, branching ; floating geo 
. small, thin, elliptical or oblong-linear, on filiform petioles ; immersed leaves ge | 
sessile, linear or lanceolate ; stipules connate, 2-ribbed; peduncles mpi 
ward ; spikes narrowly cylindrical ; achenium smooth, slightly keeled on the p- 
— Shallow ponds, North Carolina, and northward. July. — Floating leaves * 
2' iong. Immersed leaves 4! - 6' long. i 
st By: idus, 
