78 



POTAMOGETONACEAE 



Potamogeton 



o 



Map 77 

 Potamogeton americanus 

 Cham.&Schlecht 



E. Blades with the stipules more or less adnate to the base. 

 Leaves 4-8 mm wide, auricled at the base, stiffly 2-ranked, with a cartilaginous, 

 finely and sharply serrate margin or the margin entire. 



Margins of blades finely and sharply serrate ■ 21. P. Robbinsii. 



Margins entire 21a. P. Robbinsii f. cultellatus. 



Leaves less than 4 mm wide, not auricled at the base, their margins not finely 



serrate. 



Spikes from the axils of submerged leaves subglobose, sessile or on 



peduncles only a few mm long; fruit compressed, with concave sides. 



Submerged leaves obtuse, usually rounded at the tip; the connate leaf 



sheath much longer than the free stipular tip; the space between the 



midrib and faint lateral nerves usually filled with lacunae; fruit 



1.3-2.2 mm long. (Should be sought in northern Indiana.) 



P. Spirillus. 



Submerged leaves subobtuse to acute at the tip, the connate sheath about 

 half the length of the free stipular tip; midrib of leaves rarely with 



lacunae; fruit 1-1.5 mm long 5. P. diversifolius. 



Spikes from the axils of submerged leaves elongate, with separated whorls 

 of flowers, usually 1 to several cm long; fruit 3.5-4.5 mm long, usually 

 with a beak about 0.5 mm long 22. P. pectinatus. 



1. Potamogeton natans L. Map 76. All of my specimens are from 

 lakes in the northern part of the state. Usually found in all of our lakes. 



Newf. to B. C, southw. to n. N. J., Pa., Nebr., and Calif.; throughout 

 the world in temperate climates. 



2. Potamogeton americanus Cham. & Schlecht. Map 77. Frequent in 

 the lake area and rather local south of it. It is found mostly in streams, 

 and less often in lakes, dredged ditches, old canals, ponds, gravel pits, and 

 old stone quarries. 



N. B. to B. C, southw. to Fla., Tex., Calif., Mex., and W. I. ; also in the 

 Old World. 



3. Potamogeton amplifolius Tuckerm. Map 78. Frequent in our lakes 

 and very local elsewhere. I have it, however, from a dredged ditch in Jen- 

 nings County. 



N. S. to B. C, southw. to n. N. J., Ky., Mo., Kans., and Calif. 



