Natadaceae 3] 
NAIADACEAE Pond-weed Family 
Aquatic or marsh herbs, mostly immersed, with rootstocks. Leaves alternate or 
opposite, sometimes all basal, flat or terete above the stipular or sheathing base; blade 
usually present, usually entire, rarely toothed or none; reduced leaves various in shape. 
Flowers perfect or unisexual, solitary or clustered in the leaf-axils, or spirally arranged 
in a spike, or borne on a |-sided spadix, often with a spathe; pistillate flowers rarely of 2 
forms. Perianth none or of 4—6 distinct segments, or membranous and tubular or cup- 
shaped. Stamens |—2 or 4—6, filaments very short or none. Carpels 1—6, 1|-celled, 
usually J|-ovuled, distinct or united; ovary superior; style present or none. Fruit 
drupelets or nutlets or utricles. 
A. Growing in fresh water, or in salt marshes, but not in open tide-water. 
B. Leaves flat, in a few species terete, but then never more than 1.5 mm. in diameter; 
stem elongated. 
C. Leaves alternate, often wide, more than 25 mm. long when linear; pistil 1. 
D. Leaves all linear, all alternate; stamens 2; connectives of the anthers not 
dilated; fruit stalked. RupPIA (p. 31) 
DD. Often with some wide leaves, often the upper leaves opposite; stamens 4; 
connectives of the anthers dilated and perianth-like; fruit sessile. 
POTAMOGETON (p. 32) 
CC. Leaves opposite or in whorls of 3, all linear, 8—25 mm. long; pistils more 
than |: 
E. Leaves not spiny; pistils 2—10. 
F. Flowers perfect, in spikes or clusters; stamens more than 1. 
POTAMOGETON (p. 32) 
FF. Flowers monoicous, axillary; stamen 1. ZANNICHELLIA (p. 31) 
EE. Leaves spiny on the margin or the back or both; flowers solitary in the 
leaf-axils; pistil 1. Nalas (p. 33) 
BB. Leaves terete, |—-45 mm. in diameter, all basal; stem not elongated. 
LILAEA (p. 34) 
AA. Growing along tide-water shores from | m. above low tide to 2 m. below it, not 
in salt marshes. 
G. Plants growing on muddy bottom; leaves 3—-15 mm. wide; flowers monoicous; 
mature fruit rounded at base; seeds often ribbed. ZOSTERA (p. 33) 
GG. Plants growing mostly in rock crevices; leaves 4 mm. or less wide; flowers 
dioicous; mature fruit deeply cordate-sagittate at base; seeds not ribbed. 
PHYLLOSPADIX (p. 33) 
ZANNICHELLIA HORNED POND-WEED 
Submerged. Leaves entire, |-veined; stipules sheathing the leaf-bases or free. 
Flowers enclosed in a deciduous hyaline spathe. Staminate flowers of a single anther on 
a short filament. Pistillate flowers 2—5; pistils 2—-10, flask-shaped, tapering into a 
short recurved style. Mature fruit a nutlet. (Honor of G. G. Zannichelli, a botanist of 
Venice.) E. Z. palustris L. (Zannichellia) 
RUPPIA DITCH-GRASS 
Submerged. Leaves entire, |-veined, acute, wider and sheathed at base; stipular 
sheath clasping the leaf-bases. Flowers terminating a spadix-like peduncle which elongates 
and coils about the time the flower opens. Stamens 2. Pistils 4, at first sessile, at length 
