562 NAIADACE/E. (PONDWEED FAMILY). 



ans, Morong") N. Eng 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. lucens, L. Stem thick, branching, sometimes very large; leaves 

 more 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. 

 Ponds, 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 7' long), ha If -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., ( let. Stem white; foliage bright green. (Eu.) 



16. P. perfoliatus, 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 Fla., west to Minn, and Iowa. Sept., Oct. (Eu.) 



Var. lanceolatus, Bobbins. Larger; leaves long-lanceolate from a cor- 

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

 wird. 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-iuavy, 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. Mysticus, Morong. Stem very slender and irregularly branching, 

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

 5 - 7 -nerved, _/!('/// 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 J" 

 1 >ng), 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. ZOStersefblius, Schum. Stem branching, wing -flattened ; leaves 

 linear and grass-like (commonly 4' by IV'), abruptly pointed, with many Jine 

 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, 



