NAJADACEAE (PONDWEED FAMILY) 73 



smooth on the margin, fewer-nerved ; stipules broad, hyaline, obtuse, upper ones 

 acuminate ; spike 1.5-3.5 cm. long, often somewhat compound ; fruit obovoid, 

 lenticular, pitted when immature, with an acute margin and pointed with the 

 rather long style; embryo incompletely annular. (P. rufescens Schrad.) In 

 streams or ponds, Lab. to Alaska, s. to Mass., N. J., Mich., Minn., Utah, and Cal. 

 July-Sept. (Greenl., Eurasia.) 



x P. FAX6NI Morong from Ferrisburg, Vt., and x P. RECTiFdLius Benn. 

 from Chicago, 111., are infertile hybrids of nos. 5 and 6. 



6. P. americanus C. & S. Stem often branching below ; floating leaves thin- 

 nish, lance-oblong or long-elliptical, often acute, long-petioled, 4-11 cm. long, 1-3 

 cm. wide, 17-23-nerved ; submersed leaves very long (0.8-3 dm. long, 0.4-2.5 

 cm. wide), lanceolate and lance-linear, 7-15-nerved, coarsely reticulated ; 

 peduncles somewhat thickened upward ; fruit obliquely obovoid, obscurely 

 3-keeled when fresh, and distinctly so when dry, the middle keel winged above 

 and sometimes with 3-5 shallow indentations ; the rounded slightly curved face 

 surmounted by the short style ; seed with the sides scarcely impressed ; upper 

 part of the embryo circularly incurved. (P. fluitans Man. ed. 6, not Roth ; 

 P. lonchites Tuckerm.) In streams or rarely in ponds, N. B. to B. C. and 

 southw. Aug., Sept. (Eurasia, n. Afr., W. I.) 



Var. noyaeboracSnsis (Morong) Benn. Floating leaves large and thick, 

 broadly elliptic, rounded or obtuse at apex and base, 2.5-4.5 cm. wide. Ct. 

 to Wise. (Eu.) 



7. P. piilcher Tuckerm. Stem simple (very rarely branched), black-spotted ; 

 leaves of three kinds ; floating ones becoming very large (4.5-11) cm. long, 

 2-7 cm. wide), roundish-ovate and cordate or ovate-oblong, 25-37-nerved, all 

 alternate; upper submersed ones (3-5) usually lanceolate, acute at base and 

 very long-acuminate, 10-15-nerved, very thin, cellular each side of the midrib, 

 undulate, short-petioled ; lowest (2-4 near the base of the stem) thicker, plane, 

 oval or oblong with a rounded base, or spatulate-oblong, on longer petioles ; 

 peduncles thicker than the stem ; spikes 2-4 cm. long ; fruit with a rounded 

 back and angular face, pointed, distinctly 3-keeled when fresh, sharply so when 

 dry ; seed with two deep dorsal furrows, and a sinus below the angle in front ; 

 sides flat ; embryo circularly much incurved above. Ponds, local, s. Me. to 

 Fla. ; and near St. Louis, Mo. June, July. 



8. P. amplif61ius Tuckerm. Stems simple, of very variable length ; float- 

 ing leaves (sometimes wanting) large, oblong, lance-ovate or broadly elliptic, 

 abruptly acutish, 30-50-nerved, on rather long petioles ; submersed leaves often 

 very large (0.8-2 dm. long, 2.5-7 cm. broad), lanceolate or oval, acute at each 

 end, usually much recurved, undulate, mostly on short petioles ; stipules very 

 long and tapering to a point, soon becoming loose ; peduncles thickened upward, 

 in deep water much elongated ; spikes 3.5-8 cm. long; fruit very large (4-5.5 

 mm. long), rather obliquely obovoid, 3-keeled, with a broad stout beak ; seed 

 slightly impressed on the sides ; upper part of the embryo curved into a ring. 

 Ponds and rivers, N. S. to B. C., s. to N. J., Ky., Kan., and Cal. July-Sept- 



9. P. illino6nsis Morong. Stem stout, branching towards the summit ; 

 floating leaves opposite, oval or elliptic (0.5-1.5 dm. long, 4-9 cm. broad), 

 19-27-nerved, rounded or narrowed at base, with a short blunt point, on short 

 petioles ; submersed leaves oblong-elliptical, acute at each end, usually ample 

 (1-2 dm. long) ; stipules coarse, obtuse, strongly bicarinate (5-7 cm. long) ; 

 peduncles often clustered at the summit, thickening upward; spikes 4-5 cm. 

 long ; fruit roundish-obovate (3.5-4.5 mm. long), 3-keeled on the back, middle 

 keel prominent ; seed flattened and slightly impressed on the sides, obtuse or 

 pointed at base ; apex of embryo directed transversely inward. Streams and 

 ditches, 111., la., and Minn. July, Aug. 



10. P. heterophyllus Schreb. Stem slender, very branching below ; floating 

 leaves mostly thin, variable, but with a short blunt point, 9-17-nerved, 1.5-7 cm. 

 long, 0.5-2.6 cm. wide; submersed ones lanceolate, oblanceolate or linear- 

 lanceolate, acuminate or cuspidate, narrowed toward the base, somewhat stiffish, 

 2.5-8 cm. long, 0.2-1.3 cm. wide, about 7-nerved on the stem and .3-nerved on 

 the branches ; upper ones petioled, lower sessile ; stipules obtuse, loose ; pedun- 



