488 NAIADACE^. (PONDWEED FAJIILT.) 



shining ; fi-uil rounAish and compressed, tti/M obtuse margins, slighth/ heeled; em- 

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



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

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



Var. ? ConnectiCUt6llSis. 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. pr8el6ngUS, Wulfen. Stem very long, branching, flexuous ; leaves 

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

 shaped cavili/ at the extremity, thence splitting on pressure; stipules scarious, 

 very obtuse; spikes rather loose-flowered; peduncles veiy 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. perfoIi^tUS, L. Stem branching ; l^eaves orbicular, ovate or lanceo- 

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

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

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



Var. lanceolditUS. 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. Angostifolii. Leaves all submersed and similar, mostly membranaceous and 

 sessile, linear or setaceous. {No. 16, 17, and 20 are ojien gemmiparous, propa- 

 gating by narrow terminal buds detached in autumn.) 



* Stipules free from the sheathing base of the leaf. 



16. P. C0mpr6sSUS, L. (ex Fries. ) Stem branching, wing-flattened; leaves 

 linear and grass-like (commonly 4' by I^'), 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, somewhat 

 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. zosteriefolius, Schumacher.) — Still and slow-flowing waters. 

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



17. P. obtUSifdliUS, 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- 

 flowercd, 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.) 



