74 NAJADACEAE (PONDWEED FAMILY) 



cles somewhat thickened upward, mostly less than 1 dm. long ; fruit 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) Morong. Steins 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 LONGIPEDUNCULATUS (Merat) Morong. Subsimple, the inter- 

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

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

 MYRIOPHYLLUS (Bobbins) 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 perishing; those of the branches (deep 

 green) linear-oblanceolate, 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 MAXIMUS 

 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 TERRES- 

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

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

 fruit. Que. and N. E. 



11. P. angustifblius Berchtold & 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, 13-21-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 ; fruit distinctly 

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

 local, Mass, to Mich., westw. and south w. 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. SPATHAEFORMIS Tuckerm. (P. spathulaeformis Morong) in Mystic 

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



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

 submersed and similar, more or less petioled, oval or lanceolate, mucronate, 

 often crisped, frequently 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.-Oct. (Mex., W. I., Eurasia, n. Afr.) 



13. P. prae!6ngus 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 pressure ; 

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

 times reaching 5 dm.); spikes rather loose-flowered ; fruit 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, 3-11 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, 

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

 perfoliatus, var. lanceolatus 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. perfoliatus L. Similar ; leaves orbicular, ovate or lanceolate from a 

 cordate-clasping base, usually obtuse and crisped, 2-6 cm. long, 1 5-27 -nerved; 

 stipules rarely developed, less than 1 cm. long; peduncles spongy and thickish, 



