74 NAJADACEAE (PONDWEED FAMILY) 



cleg somewhat thickened upward, mostly less than 1 dm. long ; fniit small (2.5-3 

 mm. long), roundish, compressed, scarcely keeled; embryo annular above. — 

 Still or flowing water, common. July-Sept. (Greenl., Eurasia.) — Varies ex- 

 ceedingly in its submersed leaves, peduncles, etc. Forma graminifolius 

 (Fries) Moroiig. Stems much elongated and less branched, and the flaccid 

 linear-lanceolate submersed leaves 0.5-1.5 dm. long, 2-6 mm. wide ; spikes 1.5—3 

 cm. long. Forma LONGiPEDnNcnLA.TUS (Merat) Morong. Subsimple, the Inter- 

 nodes very elongate (the uppermost 1-3 dm. long) ; submerged leaves lanceo- 

 late ; peduncles 1-2.5 dm. long. — Md. to Ct., Mich., and westw. Forma 

 MYRiopHYLLUs (Robblns) Morong. Sending up from running rootstocks many 

 short repeatedly dichotomous and densely leafy stems ; fertile stems very slen- 

 der ; floating leaves small, delicate, lance-oblong, on long filiform petioles ; 

 submersed stem-leaves larger, early perisliing ; those of the branches (deep 

 green) linear-oblanoeolate, very small (1.5-3 cm. long, 2-4 mm. wide), acute; 

 spike slender, loosely flowered, 1.2-2.5 cm. long. — N. E. Forma mAximds 

 Morong. Floating leaves 0.6-1.6 dm. long, 1-3 cm. wide, very acute ; sub- 

 mersed leaves 0.5-1.6 dm. long, 0.6-1.6 cm. wide, 5-9-nerved. Forma teeees- 

 TKis Schlecht. Freely creeping in exsiccated places, producing numerous very 

 short branches wliich bear tufts of oblong or oval coriaceous leaves but no 

 fruit. — Que. and N. E. 



11. P. angustifblius Bercbtold & Presl. Resembling P. lucens, but smaller, 

 slender, much branched at base ; upper leaves coriaceous or subcoriaceous, long- 

 petioled and sometimes emersed, 0.4-1 dm. long, 1-2.5 cm. wide, 1 3-21-nerved ; 

 the others subsessile, all usually numerous, lanceolate or oblanceolate, mucro- 

 nate, undulate and crisped, shining, 0.5-1.5 dm. long, 0.5-3 cm. broad, 7-17- 

 nerved ; stipules obtuse, 1.5-4 cm. long; peduncle elongated ; /raif distinctly 

 S-Tceeled, 3-4 mm. long. (P. Zizii Mertens & Koch.) — Lakes, rarely streams, 

 local, Mass. to Mich., westw. and southw. June-Sept. (W. I., Eurasia, Afr.) 

 Var. coNNECTicuTENSis (Robbins) Benn. Larger throughout ; leaves all sub- 

 mersed ; fruit 4-4.5 mm. long. (P. lucens, var. Robbins.) — Lakes, Vt., Ct., 

 and e. N. Y. 



X P. spATHAEr6RMis Tuckemi. (P. spathulaeformis Morong) in Mystic 

 Pond, Medford, Mass., is an infertile hybrid of nos. 11 and 10. 



12. P. liicens L. Stem thick, branching, sometimes very large ; leaves all 

 submersed and similar, more or less petioled, oval or lanceolate, m,ucronate, 

 often crisped, frequeyitly shining, 6-20 cm. long, about 13-nerved; peduncles 

 often elongated ; fruit roundish and compressed, with obtuse margins, scarcely 

 keeled; embryo circularly incurved above. — Ponds, local, N. S. to Fla., w. to 

 the Pacific. Aug.-Oot. (Mex., W. I., Eurasia, n. Afr.) 



13. P. prael6ngus Wulf . Stem white, very long, branching, flexuous ; 

 leaves bright green, lance-oblong or lanceolate (0.5-3 dm. long), half-clasping, 

 obtuse with a boat-shaped cavity at the extremity, thence splitting on pressm'e ; 

 stipules white, scarious, very obtuse, 1.5-8 cm. long ; peduncles very long (some- 

 times reaching 5 dm.); spikes rather loose-flowered ; /raif obliquely obovoid, 

 compressed, sharply keeled when dry, 4-5 mm. long; style terminating the 

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

 lakes, N. S. to B. C, s. to Ct., N. J., the Great Lakes, la., Mont., and Cal. — 

 Fruiting in June and July, withdrawing the stems to deep water to mature the 

 fruit. (Eurasia.) 



14. P. Richardsbnii (Benn.) Rydb. Stem branching ; leaves long-lanceolate 

 from a cordate-clasping base, acuminate, wavy, pale bright green, 8-1 1 cm. 

 long, 13-23-nerved ; stipules conspicuous, at least as shreds ; peduncles thick- 

 ened upward, of somewhat spongy texture, elongating sometimes to 1 dm. 

 or more; spikes 1.5-3.5 cm. long; fruit irregularly obovoid, distinctly beaked, 

 obsou'ely .3-keeled, 4 mm. long, the green epicarp puckered in drying. (P. 

 perfoUatus, var. limceolatus Robbins.) — Quiet water. Que. to Mackenzie and 

 B. C, s. to N. E., N. Y., the Great Lake region, Neb., etc. July-Sept. 



15. P. perfoliitus L. Similar ; leaves orbicular, ovate or lanceolate from a 

 cordate-clasping base, usually obtuse and crisped, 2-6 cm, long, 15-27 -nerved; 

 ^fipidcf: rarehj developed, less thar\ 1 cm. long ; peduncles spongy and tliicln'sh.i 



