562 NAIADACE^E. (PONDWEED FAMILY). 



ans, Morony") N. EDg to Fla., and westward. Connecting with the next 

 section. (Eu.) 



2. Leaves all submersed and similar, mostly sessile, membranaceous and di- 

 lated, lanceolate, oblong, or oval ; stipules obtuse, becoming loose. 



14. P. Iticens, L. Stem thick, branching, sometimes very large ; leaves 

 wore or less petioled, oval or lanceolate, mucronate, often rough-serrulate, fre- 

 quently shining ; peduncles often elongated ; fruit roundish and compressed, 

 with obtuse margins, slightly keeled; embryo circularly incurved above. 

 j'ouds, N. Eng. to Fla., west to the Pacific. Aug., Sept. (Eu.) 



Var. (?) Connecticutensis, Bobbins. Stem flexuous ; leaves all sub- 

 mersed, nearly sessile, lanceolate, acuminate, crisped, not shining nor serrulate : 

 fruit larger, distinctly keeled ; nutlet thick and hard. Lake Saltonstall, East 

 Haven, Conn. 



15. P. prsel6ngUS, Wulf. Stem very long, branching, flexuous; leaves 

 lance-oblong or lanceolate (sometimes V long), half -clasp ing, obtuse with a boat- 

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

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

 reaching 20') ; fruit obliquely obovate, compressed, sharply keeled when dry ; 

 style terminating the nearly straight face ; curve of the embryo oval and lon- 

 gitudinal. Ponds and large rivers, N. Scotia to Mass., west to Minn, and 

 Iowa. Sept., Oct. Stem white ; foliage bright green. (Eu.) 



16. 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; fruit irregularly obovate, obtusely margined; 

 embryo incurved in an oval. Ponds and slow streams, common. N. Scotia 

 to Ela., west to Minn, and Iowa. Sept., Oct. (Eu.) 



Var. lanceol&tus, Bobbins. Larger; leaves long-lanceolate from a cor- 

 date-clasping base and acuminate, wavy, 3 - 4%' long ; peduncles thickened up- 

 ward. Same range as the species, and extending west to the Pacific. 



17. P. crispus, L. Stem compressed ; leaves linear-oblong, half-clasping^ 

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

 embryo incurved in a large circle. Flowing and stagnant waters, Mass, to 

 N. J. and Va., west to western N. Y. June, July. (Eu.) 



18. P. M^StiCUS, Morong. Stem very slender and irregularly branching, 

 nearly filiform (1-3 high) ; leaves oblong-linear (|- H' long by 2 -3" wide), 

 5 - 7-nerved, finely undulate and entire, obtuse or bluntly pointed, abruptly nar- 

 rowing at base, sessile or partly clasping ; spikes few, capitate (4-6-flowered), 

 on erect peduncles (1-2' long); fruit (immature) obovate, small (hardly f" 

 long), obscurely 3-keeled on the back, a little beaked by the slender recurved 

 style. Mystic Pond, Medford, Mass. 



3. Leaves all submersed and similar, mostly membranaceous and sessile, linear 



or setaceous. 

 * Stipules free from the sheathing base of the leaf. 



19. P. ZOSter8Bf61ius, Schum. Stem branching, wing -flattened ; leaves 

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

 and 3 larger nerves ; stipules (seen young) oblong, very obtuse ; spikes cylin 

 drical. 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, 



