PONDWEED FAMILY. 65 
Family 3. NAIADACEAE Lindl. Nat. Syst. Ed. 2, 366. 1836. 
Immersed aquatic plants with slender, often branching, leafy stems, the 
leaves flat or filiform, and perfect, monoecious or dioecious spicate axillary 
or spadiceous flowers. Perianth of 4 segments, or a hyaline envelope, or want- 
ing. Stamens 1-4 or occasionally more, distinct and hypogynous in the per- 
fect flowers, solitary or connate in the sterile. Anthers extrorse, 1—2-celled. 
Ovaries 1-9, mostly distinct, r-celled, mostly 1-ovuled. Carpels rarely dehis- 
cent. Seeds straight or curved. Endosperm none. 
About 10 genera and roo species of wide geographic distribution, most abundant in temperate 
‘regions. The months noted in the descriptions indicate the fruiting period. 
Flowers perfect. 
Perianth of 4 distinct segments. 1. Potamogeton. 
Perianth none ; flowers naked. 2. Ruppia. 
‘Flowers monoecious or dioecious. 
Leaves entire. 
Leaves 1-nerved, 1'-3' long, 4’' or less wide. 3. Zannichellia. 
Leaves many-nerved, 1°-s° long, 1'’-4'’ wide. 4. Zostera, 
Leaves spiny-toothed on the margins. 5. Watas. 
1. POTAMOGETON LI. Sp. Pl. 126. 1753. 
Leaves alternate or the uppermost opposite, often of 2 kinds, submerged and floating, 
the submerged mostly linear, the floating coriaceous, lanceolate, ovate or oval. Spathes 
‘stipular, often ligulate, free or connate with the base of the leaf or petiole, enclosing the 
young buds and usually soon perishing after expanding. Peduncles axillary, usually 
-emersed. Flowerssmall, spicate, green orred. Perianth-segments 4, short-clawed (Fig. 154), 
concave, valvate. Stamens 4, inserted on the claws of the perianth-segments. Anthers 
‘sessile. Ovaries 4, sessile, distinct, 1-celled, 1-ovuled, attenuated into a short erect or 
‘recurved style, or with a sessile stigma. Fruit of 4 ovoid or subglobose drupelets, the peri- 
carp usually thin and hard or spongy. Seeds crustaceous, campylotropous, with an unci- 
nate embryo thickened at the radicular end. [Greek, in allusion to the aquatic habitat. ] 
About 65 well-defined species, natives of temperate regions. Besides the following, 3 others 
-occur in the southern parts of North America. 
Stipules axillary and free from the leaf. 
With floating and submerged leaves. 
Submerged leaves bladeless. 
Nutlets more or less pitted. 1. P. natans. 
Nutlets not pitted. 2. P. Oakestanus, 
Submerged leaves with a proper blade, 
Submerged leaves of 2 kinds, lanceolate and oval or oblong. 
Uppermost broadly oval or elliptical, lowest lanceolate. 3. P. amplifolius. 
Uppermost lanceolate and pellucid, lowest oblong and opaque. 
4. P. pulcher. 
Submerged leaves all alike, capillary or linear-setaceous. 
I-nerved or nerveless. 25. P. Vaseyt. 
3-nerved. ° 26. P. lateralis. 
Submerged leaves all alike, linear. 
Nearly the same breadth throughout, obtusely pointed, coarsely cellular-reticulated 
in the middle. 5. P. Nuttallit. 
Broader at base, acute, without cellular-reticulation. 9. P. heterophyllus. 
Submerged leaves all alike, lanceolate. 
Uppermost leaves petioled, lowest sessile. 6. P. alpinus. 
All the leaves petioled. 
Floating leaves large, broadly elliptic, rounded or subcordate at base. 
r1. P. Lilinoensts. 
Floating leaves narrowly elliptical, tapering at base. 7. P. lonchites. 
Floating leaves mostly oboyate or oblanceolate, tapering at base. 
8. P. Faxont. 
All the leaves sessile or subsessile. 
Fruit only 1 line long, obscurely 3-keeled. 10. P. spathulaeformis. 
Fruit 1% lines long, distinctly 3-keeled. IN PAGING 
With submerged leaves only. 
Without propagating buds and without glands. 
Leaves with broad blades, mostly lanceolate or ovate, many-nerved. 
Leaves subsessile or short-petioled, mostly acute or cuspidate. 
13. P. lucens. 
Leaves semi-amplexicaul, obtuse and cucullate atthe apex. 14. P. praclongus. 
Leaves meeting around the stem, very obtuse at the apex, not cucullate. 
15. P. perfoliatus. 
Leaves with narrow blades, linear or oblong-linear, several-nerved. 
Leaves oblong-linear, 5-7-nerved, obtuse at the apex. 16. P. Mysticus. 
Leaves narrowly linear, 3-nerved, acute at the apex. 21. P. foliosus. 
Leaves with narrow blades, capillary or setaceous, 1-nerved or nerveless, 
ey ee confervotdes. 
*Text contributed by the late Rev. THOMAS MORONG. 
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