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. — CaUf.— 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-0. 



10. P. praelongus Wulf. Stem fiexuose, 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. — Cahf. — Alaska. Plain — Submont. Je-S. 



12. P. coznpressus 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, wdth 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. zostcracfolius 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-0. 



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 upw^ards and thicker 



than the stem; spike interrupted; fruit obliquely eUipsoid, 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. 



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

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

 nerved; peduncles clavate, about 1 cm. long; spike short, about 4-flow^ered; fruit 

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

 wmged, smuate-dentate. P. paudflorus Pursh. Ponds and streams: N.B.— 

 Fla.— N.M.— Calif.— B.C.; W. Ind. Plain— MonL Jl-Au. 



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



long; leaves filiform, 3-12 cm. long, _ __. ^ ^^^ 



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

 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— SuhinonL Je-Au. 



filiformis 



•filiform 



1-4 



