38 ZANNICHELLIACEAE 



nerves ; those of floating leaves leathery, oblong, elliptic or obovate, 3-8 cm. long, many- 

 nerved, short-petioled : peduncles 2.5-12 cm. long : spikes 1.5-2 cm. long, dense, emersed 

 or partly so: drupelets globose-obovoid, 2.5-3 mm. long, 3-keeled, the middle keel sharp: 

 embryo coiled 1^ times. 



In ponds and streams, Nova Scotia to Ontario and South Carolina. Summer. 



5. Potamogeton heterophyllus Schreb. Stems slender, 1-3.5 m. long, flattened, 

 branched : leaves various ; blades of 2 kinds, those of submerged leaves lanceolate or nar- 

 rowly linear-lanceolate, 2.5-8 cm. long, mostly sessile, with conspicuous cellular reticula- 

 tions ; those of floating leaves leathery, oval or elliptic, 1.5-4 cm. long, abruptly pointed, 

 shorter than the petioles : peduncles 2.5-15 cm. long, often thickened upward : spikes 2-4 

 cm. long, dense : drupelets nearly as broad as long, 1.5-3 mm. long, indistinctly 3-keeled 

 on the back, abruptly pointed. 



In still or flowing water, nearly throughout North America. Also in Europe. Summer and fall. 



6. Potamogeton Lonchites Tuckerm. Stems terete, 9-20 dm. long, branching : 

 leaves various ; blades of two kinds ; those of submerged leaves elongated, lanceolate or 

 oblanceolate, 10-30 cm. long, pellucid ; those of floating leaves thinnish, oblong or ellip- 

 tic, 4-15 cm. long, many-nerved, usually acute at both ends ; petioles fully as long as the 

 blades : peduncles 5 cm. long, slightly thickened upward : spikes cylindric, 2.5-5 cm. 

 long, dense : drupelets as broad as long, 3.5-4 mm. long, 3-keeled on the back, the middle 

 keel prominent. 



In ponds and rivers, New Brunswick to Washington, Florida and California. Summer and fall. 



7. Potamogeton Zizii Roth. Stems slender, elongated, branching : leaves various ; 

 blades of 2 kinds ; those of submerged leaves lanceolate to oblanceolate, 5-15 cm. long, cus- 

 pidate or acute, wavy- margined, pellucid ; those of floating leaves more less leathery, 

 elliptic, 3-10 cm. long, many-nerved, sessile or nearly so : peduncles thicker than the 

 stems, 5-15 cm. long : spikes 2.5-5 cm. long, not very dense : drupelets nearly as broad as 

 long, 2.5-3.5 mm. long, 3-keeled on the back, abruptly pointed. 



In lakes and rivers, Quebec to Montana, Florida, Texas and Wyoming. Summer. Also in Europe. 



8. Potamogeton lucens L. Stems stout, elongated, more or less branched, often 

 profusely so above : leaves all submerged ; blades elliptic or lanceolate, or oval above, 

 5-20 cm. long, acute or acuminate or sometimes mucronate, often serrulate at the apex, 

 mostly 13-nerved, short-petioled or nearly sessile : peduncles 7-15 cm. long, barely thick- 

 ened upward : spikes dense, 5-7 cm. long : drupelets 3 mm. long, blunt-tipped. 



In ponds, Nova Scotia to California, Florida and Mexico. Fall. Also in Europe. 



9. Potamogeton perfoliktus L. Stems slender, elongated, much branched : leaves 

 all submerged ; blades suborbicular to ovate or lanceolate, 2-4 cm. long, usually obtuse, 

 often serrulate at the apex, cordate-perfoliate, crisped : peduncles 2.5-3.5 cm. long, about 

 as thick as the stem: spikes 1.5-2.5 cm. long, as long as the peduncle or shorter, often 

 fruiting under water: drupelets obliquely obovoid, 2.5-3 mm. long, obscurely 3-keeled on 

 the back. 



In rivers and ponds, Newfoundland to British Columbia, Florida and California. Also in Europe. 

 Summer and fall. 



10. Potamogeton Curtissii Morong. Stems delicate, filiform, 2-4 dm. long, simple 

 or branched ; internodes elongated, naked : leaves all submerged : blades linear-filiform, 

 1-4 cm. long, 0.5-1 mm. broad, terminating in a hair-like tip, 1-nerved, sometimes with an 

 indication of 2 lateral nerves ; stipules hyaline, 6-8 mm. long, obtuse, deciduous : pedun- 

 cles slender, club-shaped, 6-12 mm. long, erect, axillary near the upper end of the stem : 

 spikes capitate, 4-6 mm. long, 3-6-flowered : fruit not seen. 



In tidal creeks, Blackwater River, Florida. Spring and summer. 



11. Potamogeton foliosus Kaf. Plants without propagating buds, or glands at the 

 base of each leaf. Stems 3-10 dm. long, flattened, much branched : leaves all submerged, 

 very numerous ; blades linear or filiform, 1.5-5 cm. long, acute, 3-nerved : peduncles some- 

 what club-shaped, 8-12 mm. long: spikes short, about 4-flowered : drupelets 1.5-2 mm. 

 long, 3-keeled ; middle keel crest-like, undulate or sinuate-toothed, often with tooth-like 

 shoulders at each end. 



In streams and ponds, New Brunswick to British Columbia, Florida and California. Summer. 



12. Potamogeton pusillus L. Plants with both propagating buds and glands at the 

 base of each leaf. Stems filiform, 1-6 dm. long, branched : leaves all submerged, numer- 

 ous ; blades linear or linear-filiform, 2-8 cm. long, acute, 1-3-nerved, usually 2-glandular 

 at the base : peduncles slender, 6-20 mm. long, or rarely 10 cm. long : spikes 3- 10- flowered, 

 capitate or interrupted : drupelets longer than broad," 1.5-2 mm. long, 2-grooved on the 

 back or with 3 distinct keels, crestless. 



In slow streams and ponds, New Brunswick to British Columbia, North Carolina, Texas and Cali- 

 fornia. Summer. Also in Europe. 



