24 ZANNICHELLIACEAE 



leaves mostly adnate; emersed peduncles 6-15 mm. long; submerged ones 4-6 

 mm. long, clavate, as long as the spikes; emersed spikes 3.5-7 mm. long, often 

 interrupted; fruit cochleate, about 1 mm. long, 3-keeled, the middle keel narrowly 

 winged. Still water: Me. Fla. Tex. Calif .Mont.; Mex. Je-S. 



9. P. lucens L. Stem thick, branched, leafy; leaves submerged, lliptiec 

 or lanceolate, or the uppermost oval, thin, shining, acute or acuminate, or rarely 

 rounded at both ends and merely mucronate, 6-20 cm. long, 15-40 mm. wide, 

 the ends often serrulate; peduncles 7-15 cm. long; spike cylindric, 3-6 cm. long, 

 thick; fruit roundish, 3 mm. long, 2.5 mm. thick. Ponds: N.S. Fla. Mex. 

 Calif.; Eu., C. Am., and W. Ind. Plain Mont. Au-O. 



10. P. praelongus Wulf. Stem flexuose, white, often 25 dm. long, flattened, 

 much branched; leaves submerged, oblong-lanceolate, thin, bright green, semi- 

 amplexicaul, 0.5-3 dm. long, 1-4 cm. wide, with 3-5 principal nerves; peduncles 

 7-50 cm. long, straight, as thick as the stem; spike cylindric or globose, 1-3 

 cm. long; fruit obliquely obovoid, 4-5 mm. long, 3-4 mm. thick; middle keel 

 sharp; style short. Ponds and streams: N.S. N.J. Minn. Calif. B.C.; Eu. 

 Je-Au. 



11. P. Richardsonii (A. Bennett) Rydb. Stem very leafy and much 

 branched; leaves submerged, thin, lanceolate, 5-10 cm. long, 8-15 mm. wide at 

 the broadened amplexicaul base, 13-23-nerved, acute or acuminate and incurved 

 at the apex; peduncles 3-4 cm. long, thickened upwards; spike cylindric, 2-2.5 

 cm. long; fruit about 4 mm. long, 2.5 mm. thick, obscurely 3-keeled. P. 

 perfoliatus lanceolatus Robbins. P. perfoliatus Richardsonii A. Bennett. Ponds 

 and lakes: N.Y. Del. Wyo. Calif. Alaska. Plain Submont. Je-S. 



12. P. compressus L. Stem branching, much flattened, often winged; 

 leaves submerged, linear, obtuse or mucronate, 5-30 cm. long, 2-4 mm. wide, 

 with 3 principal veins and many fine ones; peduncles 4-10 cm. long; spike cylin- 

 dric, 12-15-flowered, about 1 cm. long; fruit obovoid, with a broad base, about 

 4 mm. long, 2.5-3 mm. thick, 3-keeled on the back; style short, recurved. The 

 plant often propagates by means of terminal leaf -buds. P. zosteraefolius Schum. 

 Ponds and slow streams: N.B. N.J. Sask. Ore. B.C.; Eu. Plain. Jl-S. 



13. P. obtusifolius Mert. & Koch. Stem slender, branched above, more or 

 less compressed; leaves linear, obtuse or mucronate, 5-8 cm. long, 1-4 mm. wide, 

 usually 3-nerved, with a broad midrib, and 2 translucent glands at the base; 

 peduncles 2-3 cm. long, slender, erect; spike ovoid, 5-8-flowered, 6-8 mm. long; 

 fruit obliquely obovoid, 3 mm. long, 2 mm. thick, 3-keeled; style short. Still 

 water: Que Kans. Wyo. Pa.; Eu. Jl-O. 



14. P. Friesii Rupr. Stem compressed, branching, 5-12 dm. long; leaves 

 linear, 4-7 cm. long, about 2 mm. wide, obtuse or mucronate at the apex, 5- 

 (rarely 7-) nerved; peduncles 2-4 cm. long, often thickened upwards and thicker 

 than the stem; spike interrupted; fruit obliquely ellipsoid, about 2 mm. long, 

 2-grooved on the back, usually with a shallow pit on the sides; style recurved. 

 P. compressus Oeder, not L. Still water: N.B.N.Y. Minn. B.C.; Eu. 

 Jl Au. 



15. P. foliosus Raf. Stem very slender, branched, flattened, 3-10 dm. long; 

 leaves very narrowly linear, almost filiform, 3-5 cm. long, 0.5-1 mm. wide, 3- 

 nerved; peduncles clavate, about 1 cm. long; spike short, about 4-flowered; fruit 

 lenticular, almost orbicular, 2 mm. long, 3-keeled on the back; middle keel 

 winged, sinuate-dentate. P. pauciflorus Pursh. Ponds and streams: N.B. 

 Fla. N.M. Calif. B.C.; W. Ind. PlainMont. Jl-Au. 



16. P. pusillus L. Stem very slender, filiform, much branched, 1.5-6 dm. 

 long; leaves filiform, 3-12 cm. long, 0.5-1.5 mm. wide, 1-3-nerved; peduncles 

 5-30 mm. long, rarely 3-6 cm. long; spike 3-10-flowered; fruit obliquely ellipsoid, 

 about 2 mm. long, 1 mm. thick, 2-grooved on the back, not keeled. It propa- 

 gates often by buds. Ponds and slow streams: N.S. Va. Tex. Mex. Calif. 

 B.C. Yukon; Eu. Plain Submont. Je-Au. 



17. P. filiformis Pers. Stem slender, filiform above, branching, leafy, 1-4 

 dm. long; leaves linear-filiform, 5-30 cm. long; free portion of the stipules 3-5 cm. 



