488 NAIADACE^E. (PONDWEED FAMILY.) 



shining ; fruit roundish and compressed, with obtuse margins, slightly kedtd ; em- 

 bryo circularly incurved above. Ponds : not common. Aug., Sept. (Eu.) 



Var. minor, Nolte. Smaller ; upper leaves distinctly petioled and sometimes 

 emersed, the others subsessile, all usually numerous, undulate and shining. 



Var. ? Connecticutensis. Stem flexuous ; leaves all submersed, nearly 

 sessile, lanceolate, acuminate, crisped, not shining ; fruit larger, distinctly keeled; 

 nutlet thick and hard. Saltonstall's pond, East Haven, Connecticut, 1850. 



13. P. prsel6ngUS, Wulfen. Stem very long, branching, flexuous ; leaves 

 lance-oblong or lanceolate (sometimes 7' long), half -clasping, obtuse with a boat- 

 shuped cavity at the extremity, thence splitting on pressure; stipules scarious, 

 very obtuse; spikes rather loose-flowered; peduncles very long (sometimes reach- 

 ing 20') ; fruit obliquely obovate, compressed, sharply keeled when dry ; style ter- 

 minating the nearly straight face ; curve of the embryo oval and longitudinal. 

 Ponds and large rivers, E. New England, and along the Great Lakes to Lake 

 Superior. Sept., Oct. Stem white : foliage bright green. (Eu.) 



14. P. perfoli&tUS, L. Stem branching ; leaves orbicular, ovate or lanceo- 

 late from a cordate-clasping base, usually obtuse and often minutely serrulate ; 

 peduncles short, cylindrical ; fntit irregularly obovate, obtusely margined; embryo 

 incurved in an oval. Ponds and slow streams : common. Sept., Oct. (Eu.) 



Var. lanceoltus. Larger; leaves long-lanceolate from a cordate-clasping 

 base and acuminate, wavy, 3' to sometimes 4' long ; peduncles thickened upwards. 

 Along the Great Lakes. This form seems peculiarly American. 



15. P. crispUS, L. Stem compressed; leaves linear-oblong, half-clasping, ob- 

 tuse, serrulate, crisped-wavy, 3-nerved; fruit long-beaked; upper portion of the em- 

 bryo incurved in a large circle. Flowing and stagnant waters, Delaware, 

 Penn., and New Jersey, Tatnall, Porter, Meehan. June, July. (Eu.) 



3. ANGUSTIFOLII. Leaves all submersed and similar, mostly membranaceous and 

 sessile, linear or setaceous. (No. 16, 17, and 20 are often yemmiparous, propa- 

 gating by narrow terminal buds detached in autumn.) 



# Stipules free from the sheathing base of the leaf. 



16. P. COmpr^SSUS, L. (ex Fries.) Stem In-anching, wing flattened ; leaves 

 linear and grass-like (commonly 4' by 1^'), abruptly pointed, with many fine and 

 3 larger nerves; stipules (seen young) oblong, very obtuse ; spikes cylindrical, 12 - 

 15-flowered, not half as long as the peduncle; fruit obliquely obovate, someAvhat 

 keeled and with slight teeth on the back, the sides not impressed, the face arch- 

 ing and terminated by the short style ; summit of the large embryo lying transverse 

 to the fruit. (P. zostersefolius, Schumacher.) Still and slow-flowing waters, 

 New England to Penn. and Wisconsin: not common. Aug., Sept. (Eu.) 



17. P. obtUSif61ius, Mertens & Koch. Stem flattened, very branching, 

 leaves linear, tapering towards the base, obtuse and mucronate or very acute, 3- 

 (rarely 5-) nerved; stipules elongated, very obtuse; spike ovate, continuous, 5-8- 

 flowered, about the length of the peduncle ; fruit oval, apiculate with the style, not 

 keeled when fresh, upper portion of embryo coiled inward and lying transverse to 

 the fruit. Slow streams and ponds : very rare : Dillerville swamp, near Lan- 

 caster, Penn., Prof. Porter. Swamp of Beaver pond, near Central mine, and 

 floating in Gratiot Lake, N. Michigan. Sept., Oct. (Eu.) 



