PONDWEED FAMILY 99 
17. P. angustifolius, Berchtold & Prest. Resembles P. lucens, but is 
smaller and whereas all the leaves of P. lucens are submersed the upper 
leaves of this form are sometimes floating on the surface. The fruit of 
this species is 3-keeled while that of P. lucens is roundish and scarcely 
keeled. Lakes, Vt., Conn., and N. Y. 
18. P.lucens, L. (Fig. 4, pl. 4.) Swuintna Ponpweep. Leaves 3 
to 4 in. long, 1 in. broad, lance-shaped or the uppermost oval, often shin- 
ing. Leaf stalks short, flower stalk often 4 to 6 in. long. Through our 
area. 
Var. P. lucens connecticutensis, Robbins; leaves crisped, not shining. 
Conn. and N. Y., rare. 
19. P. Zizii, Roth. Z1z’s PonpweEp. Smaller than P. lucens, but 
much like it. Branched at base. Floating leaves elliptic, 2 to 4 in. long 
with long leaf-stalks. Submersed leaves long, lance-shaped, wavy, the 
surface shining, on long leaf-stalks. Flowers on stems thicker than the 
general stem. Flower spikes 1 to 2 in. long. Lakes and streams 
throughout our region. 
20. P. praelongus, Wulf. WHITE-STEMMED PoNDWEED. Very long 
stem, leaves broader at base and half clasping the stem. Stems white. 
Some leaves 12 to 14 in. long. 
21. P. mysticus, Morong. Mystic PoNpWEED. Plant slender, upper 
leaves lance-ovate, opposite, 1 to 14 in. long, 1/12 to 4 in. wide. Lower 
leaves alternate, longer than the upper. No leaf stalks. Stipules gen- 
erally small. Spikes with 4 to 6 flowers. Ponds in Mass. 
22. P. crispus, L. (Hilger plo) CURLED-LEAVED PONDWEED. 
Leaves oblong, rounded at summit, wavy, half clasping at base, 2 to 4 
in. long, 1/3 as wide. Spikes with few more or less scattered flowers. 
Fresh or sometimes brackish water, Mass. and southward. 
C. Leaves very narrow, grass-like or thread-like. 
23. P. obtusifolius, Mertens & Koch. BLUNT-LEAVED PONDWEED. 
Leaves very narrow grass-like, 3-veined, 2 to 3 in. long, 1/20 to 3/20 in. 
wide, very obtuse at extremity. Stipules rather long and also very 
obtuse. Spike 5 to 8 flowered. Fruit not keeled. Our region, in still 
waters. 
24. P, zosteraefolius, Schum. (Fig. 9, pl. 5.) Een Grass Ponp- 
WEED. Leaves similar to No, 23, but often much longer and less obtuse 
at extremity. Indefinitely veined. Fruit keeled. Stipules falling early. 
Still or running waters, N. J. and northward. 
25. P. Hillii, Morong. HiLL’s Ponpwerep. Leaves narrow. grass-like 
1 to 3 in. long, pointed at free extremity. Ponds, Eastern N. Y., west- 
ward. 
26. P. foliosus, Raf. Leary Ponpwerep. Stem thread-like; leaves 
very narrow 1 to 2 in. long, sharp pointed; stipules obtuse; fruit dis- 
tinctly keeled. Ponds and streams, our region. 
27. BP. Friesii, Rubrecht. Fries’s Ponpweep. Stems 2 to 4 ft. long. 
Plant resembles No. 23 but stipules are acute. Still waters, N. Y. and 
westward, 
