457 
++ Submersed leaves lanceolate, rarely oval or linear: spikes dense, many-flowered, on 
stout peduncles, 
3. P. rufescens Schrad. Stem simple: floating leaves (often wanting) 5 to 12 em. 
long, rather thin, wedge-oblanceolate, narrowed into a short petiole, 11 to 17-nerved; 
submersed leaves almost sessile, lanceolate and lance-oblong, fewer-nerved; stipules 
broad, hyaline, obtuse, the upper acuminate: fruit obovate, lenticular, pitted when 
immature, acutely margined, beaked with rather long style.—In streams and ponds, 
extending from the Atlantic States to Texas. 
4. P. fluitans Roth. Stems branching: floating leaves thinnish, lance-oblong or 
long-elliptical, long-petioled, 17 to 23-nerved; submersed leaves very long (1 to 
3 dm.), lanceolate and lance-linear, 7 to 15-nerved, coarsely reticulated: peduncles 
thickened above: fruit obliquely obovate, 3-keeled (the middle keel winged above): 
style short: nutlets with the sides seareely impressed. (P. lonchites Tuckerm.)— 
In streams, extending from the Atlantic States to Central Mexico. 
** Leaves all submersed, uniform, mostly sessile, membranaceous and dilated, lanceolate 
to oval, numerous ; stipules obtuse, becoming loose. 
5. P.lucens L. Stem thick and branching: leaves more or less petioled, oval or 
lanceolate, mucronate, often rough-serrulate, frequently shining ; stipules large: 
peduncle often elongated: fruit roundish, compressed, with obtuse margins, slightly 
keeled.—From San Antonio to the Rio Grande. 
6. P. perfoliatus L., var. lanceolatus Robbins. Larger: leaves long-lanceolate, 
from a cordate-clasping base, acuminate, wavy, 7 to 11 em. long: peduncles thick- 
ened upward.—Apparently across the continent. 
*** Leaves all submersed and similar, thin, sessile, linear or setaceous. 
7. P. foliosus Raf. Stem filiform, flattish, and much branching: leaves narrowly 
linear (2.5 to 5em. long), acute, obscurely 3-nerved; stipules obtuse, free from the 
sheathing base of the leaf: spikes capitate, 1 to 4 (usually 2)-flowered, on short ela- 
vate peduncles: fruit roundish lenticular, the back more or less crested. (P, pauci- 
Jlorus Pursh, not Lam.)—Stagnant waters of the Limpia. 
8. P. pectinatus L. Stem filiform, repeatedly dichotomous: leaves very narrowly 
linear, attenuated at apex, l-nerved with a few transverse veins; stipules united 
with the sheathing base of the leaf: spikes interrupted, on long filiform peduncles: 
fruit obliquely broad-obovate, compressed, bluntly keeled: shell of nutlet very 
thick.—Throughout northern and central Texas, 
2.RUPPIA LL. (Diren-Grass. ) 
Marine herbs, with long filiform forking stems. slender almost eapil- 
lary leaves (sheathing at base), two or more perfect flowers on a slender 
spadix which is at first inclosed in the sheathing spathe-like base of a 
leaf, no perianth, two sessile stamens each with two large separate 
anther-cells, 4 small sessile ovaries, sessile depressed stigma, small 
obliquely ovate pointed drupe on slender stalk, and the spadix also 
raised on an elongated filiform peduncle. 
1. R. maritima 1. Leaves linear-capillary: nut ovate, obliquely erect, 3 mm. 
long: fruiting pedicel capillary, 7 to 15 cm. long: stipes 2 to 24 mm. long.—Shallow 
saline waters, near Brazos Santiago. 
3. ZANNICHELLIA Micheli. (HORNED POND-WEED.) 
Slender branching herbs, with mostly opposite long-filiform leaves, 
sheathing membranaceous stipules, naked sessile monacious axillary 
flowers; the sterile consisting of a single stamen with a slender fila- 
