40 ZANNICHELLIACEAE 



3. POTAMOGETON L. 



Herbs growing mostly in fresh water. Leaves various, the submerged and 



floating mainly different. Flowers perfect, spicate. Stamens 4, with appendaged 



anthers. Carpels 4. Drupelets 4 together, spicate, sessile. Pondweed. 



Stipules axillary, free from the leaf. 



Plants with both submerged and floating leaves. 

 Submerged leaves without blades. 



Floating leaves with ovate or oval blades subcordate or rounded at the base: flowering 



spikes 3-6 cm. long, 5-6 mm. thick. 1. P. naians. 



Floating leaves with narrowly elliptic blades acute at both ends: 



flowering spikes 1-2 cm. long, 2.5-4 mm. thick. 2. P. Floridanus. 



Submerged leaves with normal blades. 

 Blades of submerged leaves of 2 forms. 



Blades of the floating leaves cordate at the base: drupelet-beak erect. 3. P. pulcher. 

 Blades of the floating leaves rounded at the base: drupelet-beak 



oblique. 4. P. amplifolius. 



Blades of submerged leaves all like. 



Submerged leaves with linear or nearly linear blades. 



Leaf-blades with coarse cellular reticulation in the middle. 5. P. epihydrus. 



Leaf-blades with inconspicuous cellular reticulation. 6. P. heterophijllus 



Submerged leaves with lanceolate or oblanceolate blades. 



Leaf-blades distinctly petioled. 7. P. Americanus. 



Leaf-blades sessile or nearly so. 8. P. angustifolius 



Plants with submerged leaves only. 

 Leaf-blades broad. 



Blades short-petioled or nearly sessile. 9. P. hicens. 



Blades clasping the stem. 10. P. perfoliatus. 



Leaf-blades linear or filiform. 



Blades 1 -nerved. 11. P. Curtissii. 



Blades 3-nerved. 



Drupelets crested: plants without propagating buds or glands. 12. P. foliosus. 

 Drupelets crestless: plants with both propagatmg buds and glands. 13. P. pusillus. 

 Stipules adnate to the blades or the petioles of the submerged leaves. 



Plants with both submerged and floating leaves: druplets crested. 14. P. diversifolius 



Plants with submerged leaves only: drupelets crestless. 15. P. peciinatus. 



1. Potamogeton natans L. Leaves of 2 kinds, the submerged phyllodia, the 

 floating ones with ovate or oval blades 4-9 em. long, rounded or subcordate at the 

 base: anthers notched at the apex: drupelets obovoid, 4-4.5 mm. long, scarcely 

 keeled. 



In still water or streams, Nova 8cotia to British Columbia, Pennsylvania, Tennessee, 

 Nebraska and California. Also in Europe and Asia. Summer. 



2. Potamogeton Floridanus Small. Smaller than P. natans: floating leaves 

 with narrowly elliptic blades 4-7 cm. long, acute at both ends: anthers apiculate at 

 the apex: drupelets smaller than in P. natans. 



In the Blackwater River, Florida. Spring and summer. 



3. Potamogeton piilcher Tuckerm. Leaves of 3 kinds, the lower submerged 

 ones leathery, the blades spatulate to ovate, the upper submerged ones narrower, 

 flimsy, the floating leaves with leathery ovate or orbicular-ovate cordate blades: 

 drupelets turgid, 4-4.5 mm. long, 3-keeled. 



In ponds, Maine to British Columbia, Georgia and Arkansas. Summer. 



4. Potamogeton amplifolius Tuckerm. Leaves of 3 kinds, the lower submerged 

 ones with lanceolate blades acute at each end, the upper submerged ones mostly 

 smaller than the lower ones; blades elliptic to oval, the floating leaves with thick 

 ovate or oval blades rounded at the base: drupelets turgid, 4-5 mm. long, the 

 middle keel prominent. 



In streams and ponds. Nova Scotia to British Columbia, Florida, Arkansas and Cali- 

 fornia. Summer. 



5. Potamogeton epihydrus Eaf . Leaves of 2 kinds, the submerged with linear 

 5-nerved blades, the floating ones with oblong, elliptic or obovate blades 3-S cm. 

 long: druplets globose-obovoid, 2.5-3 mm. long, the middle keel sharp. [P. Nuttallii 

 Cham. & Schlecht.] 



In ponds and streams, Newfoundland to British Columbia, South Carolina and Iowa. 

 Summer. 



6. Potamogeton heterophyllus Schreb. Leaves of 2 kinds, the submerged 

 narrowed upward, inconspicuously reticulated, the floating ones with oval or elliptic 

 blades 1.5-4 cm. long, abruptly pointed: drupelets 1.5-3 mm. long, indistinctly 

 3-keeled. 



In still or flowing water, nearly throughout the United States and southern Canada. 

 Also in Europe. Summer and fall. 



7. Potamogeton Amerlc&nus Cham. & Schlecht. Leaves of 2 kinds, the sub- 

 merged with elongated blades, the floating ones with oblong to elliptic long-petioled 



