NAIADACEX. (PONDWEED FAMILY.) 445 
1. Z. marina, L. Stem slender, terete, jointed; leaves thin and tender, 
faintly 3-5-nerved; flowers in two rows on the linear spadix. — Deep salt- 
watercoves. West Florida, and northward. Aug. and Sept. 
3. ZANNICHELLIA, L. 
Flowers moneecious, axillary. Sterile flower consisting of a solitary naked 
filament bearing a 2-4-celled anther. Fertile flower from the same axil, com- 
posed of 2 — 6 sessile 1-celled ovaries, surrounded by a cup-shaped involucre, and 
pointed with the slender style. Stigma obliquely peltate. Ovule suspended, 
orthotropous. Achenium oblong, stalked. Embryo slender, coiled. — Sub- 
merged aquatic plants, with filiform branching stems, and very narrow and 
entire alternate leaves, with sheathing stipules. 
1. Z. palustris, L. Stems tufted, filiform, alternately branched ; leaves 
narrowly linear, entire, acute, l-nerved ; anther 2-celled, on a long and slender 
filament ; achenia 3-6 in a cluster, commonly raised on a short common pe- 
duncle, each stalked, linear-oblong, somewhat compressed and curved, smooth 
and wingless, about one third longer than the persistent style. — Fresh or brack- 
ish water, West Florida, and northward. May - Aug. — Stems 1°-3° long. 
Leaves 1! - 2! long. 
E 4. RUPPIA, L Dicmomss 4 00 000 
Flowers perfect, naked, two or more on a slender spadix, enclosed in the 
spathe-like sheaths of the leaves, but soon long-exserted. Stamens 2, closely 
sessile : anther-cells large, distinct. Ovaries 4, sessile, containing a single sus- 
pended campylotropous ovule. Stigma peltate. Achenium stalked, obliquely 
ovate. Embryo pointed by the short plumule. — Salt-water herbs, with filiform 
' branching stems, and alternate linear or bristle-like sheathing leaves. 
E. R. maritima, L.— In shallow water, along the coast, Florida, and 
northward. May- Aug. — Stems immersed, 19-30 long, mostly creeping at 
the base. Leaves filiform, 1'—3' long, with dilated membranaceous sheaths. 
Fruiting peduncles 1’-4! long. Achenium pointed. 
5. POTAMOGETON, Tourn. Ponpwesp. 
Flowers perfect, spiked. Sepals 4, roundish, valvate in the bud. Stamens 
4, opposite the sepals: filaments short: anthers 2-celled. Ovaries 4, sessile. 
Ovules ascending, campylotropous. Style short or none: stigma peltate. 
Achenia 1-4, compressed. Embryo curved or coiled. — Aquatic herbs, with 
immersed slender and jointed stems. Leaves stipulate, alternate and opposite, 
either all immersed and commonly membranaceous, or the upper ones floating 
And more rigid. Spikes peduncled, axillary and terminal. 
: * Leaves all immersed and alike. 
. „ P. pectinatus, L. Stem slender, flexuous; the branches 
forking, distichous ; leaves long, thickish, slightly channelled, appros 
on 
