PONDWEED FAMILY 95 
groups, the corolla absent or of various forms. The stamens con- 
sist of the anthers only, being without filaments or with only the 
rudiments of filaments. The stamens and pistil may occupy the 
same flower or separate flowers. 
Flowers on fleshy spikes. Perianth, when present, 4-parted. 
Eoundein? tres water. (L.'s « “Potamogeton 
Flowers without perianth, on a long-grooved receptacle which 
is nearly hidden by the grass-like leaf. Marine plant 
: : St veoh Se ee : Zostera 
Flowers hee iihant mocinatth fruit arranged in a false umbel 
surmounting a tall spiral fruit stalk . . . . Ruppia 
Flowers naked, pear-shaped, green, in small radiating groups 
inthe axils of the leaves..... |)» #40. aanmiehellia 
Margins of leaves spiny-toothed. Pistillate and staminate 
flowers on different plants. Pistil solitary, naked . Naias 
1. POTAMOGETON, L. 
Aquatic plants mostly in shallow pools or streams of fresh water, with 
inconspicuous, greenish or sometimes dull reddish masses of flowers ar- 
ranged on a fleshy pediceled spike, perianth 4-parted, stamens 4; ovaries 
4; leaves all submersed or, the uppermost spreading into a long narrow 
or a rounded oval expanse, floating on the surface of the water. Lower 
leaves alternate, upper generally opposite. Lower leaves quite thin, mem- 
braneous; the floating leaves leathery and firm in structure. Stipules 
thin and generally resembling the membraneous leaves, they are, in some 
species, several inches in length. 
Group 1: Upper leaves floating on the surface of the water and differing 
from the submersed leaves in form and texture. 
This group is again divided into two sections. 
Sec. 1. Floating leaves more or less heart-shaped at base, sometimes but 
slightly so. 
1. P. natans, L. (Fig. 1, pl. 4.) Common PonpWEED. Stem 2 to 
4 ft. long; floating leaves 2 to 4 in. long, half as wide, on long leaf stems 
which are as thick as the main stem. Leaves elliptic or ovate, obtuse, 
tipped with an abrupt point at outer extremity. The nutlet has a deep 
impression down the middle. Leaf wings (stipules) very long (4 to 6 
in.) ; spike of flowers 1 to 2 in. long, dull green, protruding above the 
surface of the water. Common in still ponds and borders of lakes and 
streams. 
2. P. Oakesianus, Robbins. (Fig. 1, pl. 5.) OAKEs’s PONDWEED. 
Stems more slender than those of No. 1. Leaf stems thicker than the 
main stem. No groove on the side of the nutlet. Leaves elliptic, very 
