70 PUBLIC HEALTH BULLETIN NO. 286 



14. Leaves undulate or crisped with 3-7 promi- 11. P.perfoliatus. 

 nent nerves. 



14. Leaves flat and with 1 prominent nerve 12. P. bupleuroides. 



15. Leaves ribbon-like, more than 2 mm. wide 4. P. epihydrus. 



1 5. Leaves narrower, usually filiform 16. 



16. Stipules united to base of leaf forming a 13. P. pectinatus 

 sheath more than 1 cm. long; fruits on 

 spike interrupted appearing like beads on 

 a string. 

 16. Stipules not united to leaves or if united 17. 

 forming a sheath much less than 1 cm.; 

 fruits continuous on spike. 

 17. Plants with axillary globular spikes as well as cylindric 18. 

 terminal spikes; fruit flat and spiralled like a snail 

 shell. 

 17. Plants with terminal cylindric spikes only; fruit plump. 19. 



18. Submerged leaves 0.5-2 mm. wide, not taper- 2. P. diversifolius. 

 ing to a long point; floating leaves, when 

 present, rounded at the tip, the larger 5-15 

 nerved. 

 18. Submerged leaves 0.1-0.6 mm. wide, tapering 3. P. capilloceus. 

 to a long point; floating leaves, when 

 present, pointed at the tip, 3-7 nerved. 



19. Leaves without basal glands 14. P. foliosus. 



19. Leaves with a pair of glands at base of leaf 15. P. berchtoldi. 



1. P. natans L. — Found in various provinces but known only from 

 northern part of our territory in Tennessee. 



2. P. diversifolius Raf. Pondweed.— One of our more common 

 Pondweeds, found in various provinces over most of our territory, 

 although no positive record from Florida. Anopheles quadrimaculatus 

 sometimes found associated. 



3. P. capillaceus Poir.^-Very similar to preceding but more char- 

 acteristically Coastal Plain in distribution, found in all of our States 

 except Tennessee. In Tennessee there are a few stations for the very 

 similar P. hicujtulatus Fernald which may be distinguished by its light 

 brownish fruits with a coarsely toothed keel from P. capillaceus with 

 its greenish fruit with an entire or finely toothed keel. P. capillaceus 

 is often found in rather acid waters. 



4. P. epihydrus Raf.^ — ^Known in our territory only from highland 

 areas in Georgia, North Carolina, and Tennessee. 



5. P. pulcher Tuckerm. — Found in ponds in various provinces, 

 range includes all of our territory, not frequent. 



6. P. amplifolius Tuckerm. — Range similar to preceding, found 

 mostly in hard waters. 



7. P. nodosus Poir. — One of the more common Pondweeds, found 

 in various provinces, range includes all of our territory, commonly 

 referred to as Potamogeton americanus C. & S. 



