4. POTAMOGETON. 
Perianth segments 4. Carpels sessile. 
5. RUPPIA. 
Perianth none. Carpels long-stipitate. Fruit in umbels. 
$ Zannichelliz. 
Flowers axillary. Perianth none or hyaline. Stamen 1 with 
elongated filament, or of 2 or 3 connate, sessile anthers. Ovaries 
2-9, t-ovuled; ovules pendulous from the top of the cell, ortho- 
tropous. 
6. ZANNICHELLIA. 
Perianth none. Stamen І, with a short filament. Carpels 2-9, 
a little curved. Fruit in umbels. 
3 Naize. 
Flowers moncecious or dicecious, axillary. Perianth a hyaline 
envelope. Stamens of І sessile or 2 connate anthers. Ovaries 
solitary, I-ovuled; ovules anatropous. Embryo oblong. 
7. Natas. 
Flowers solitary or glomerate. 
$ Zosterez. 
Marine plants with long linear leaves. Flowers moncecious 
or dicecious, on an enclosed spadix. Perianth none. Ovaries I, 
sessile, 1-ovuled; ovules pendulous, orthotropous. Embryo 
straight. 
8. ZOSTERA. 
Flowers moncecious. Carpels ovoid. 
9. PHYLLOSPADIX. 
Flowers dicecious. Carpels heart-shaped. 
1. TRIGLOCHIN, L. Sp. Pl. 338 (1753). 
Marsh plants with radical, semiterete, fleshy leaves, which have 
membranous, often ligulate, sheaths at the base. Flowers per- 
fect, in spikes or racemes, on long, smooth, naked scapes. Seg- 
ments of the perianth 3-6, concave, the 3 inner inserted higher 
than the others. Stamens 3-6; anthers 2-celled, sessile or nearly 
so, inserted at the base of the segments and attached by the back, 
extrorse and with the segments deciduous. Ovaries 6, united or 
