CXXIX. NAIADEA. 387 
Fresh-water or salt-marsh plants. 
Flowers in dense, many-flowered spikes; perianth 
4-parted; stamens4 . . 
eee icoiaw ein. ee POMANTOG ETON: 
Flowers 2 or more on a slender spadix; perianth 0; 
POTS A) MMe irely (el Nis Mates oii, Wivicdes. is tf surged RUPP LA, 
Flowers solitary and sessile in the axils of the leaves ; 
perianthO; stamenl ........ . & ZANNICHELLIA. 
Marine, submerged in the sea. 
Spadix flat, bearing anthers and ovaries in a double 
row, onits upperside . . . . « . i+ «. 4 ZOSTERA. 
1, POTAMOGETON, Linn. 
Flowers bisexual. Perianth 4-parted. Stamens 4, opposite 
the parts of the perianth; anthers subsessile, 2-celled, ex- 
trorse. Carpels 4; style short or 0; stigma oblique. Nuts 
4, distinct.— Kunth, l. c. p. 127; Endl. Gen. n. 1664. 
Caulescent, aquatic, submerged or floating plants. Leaves alternate, 
very rarely opposite, stipulate. Stipules connate, separate from the petiole or 
leaf, rarely joined with the petiole in a sheath. Spikes spadix-like, pedun- 
culate, nude, terminal or axillary.—P. natans, a nearly cosmopolitan spe- 
cies, is found in the colony. 
2. RUPPIA, Linn. 
Flowers bisexual, 2 or more sessile on a filiform, axillary 
spadix, at first included in the leaf-sheath, then exserted. 
Perianth 0. Stamens 2, opposite ; filaments very short, scale- 
like ; anthers large, extrorse, 2-celled, cells parallel, distinct, 
easily separating. Carpels 4, free, keeled at back, gradually 
becoming stalked. Drupes 4 or fewer, on long stalks, com- 
pressed, gibbous, crowned with the sessile, discoid stigma.— 
Kunth, l.c. p. 122; Endl. Gen. n. 1661. 
R. maritima is a small submerged plant, growing in estuaries or some- 
times in fresh or brackish water, near the sea. It has much the aspect of 
Zannichellia, but different floral characters. I gathered it in 1838 in a 
* Vley,” near the Lighthouse, Greenpoint ; fruiting in December. 
3. ZANNICHELLIA, Mich. 
Flowers monecious or polygamous (male and bisexual), 
solitary in the axils of the leaves, sessile. Perianth 0. Male: 
Stamen 1; filaments filiform ; anthers 2-celled, cells divergent 
at base. Hermaphrodite: Stamen 1, lateral. Carpels 4, 
free, convex-backed, sessile, with a short cup-like sheath at 
base; ovule solitary, pendulous; style short; stigma peltate, 
disk-like. Nuts 4, subsessile or stipitate, obliquely oblong, 
compressed, beaked with the persistent style, more or less 
toothed or crested at back.—Kuwnth, l.c. p. 123; Endl. Gen. n. 
1662. 
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