8 ALISMALES 
Stipules adnate to the base of the leaves. 
Peduncles of the submerged spikes 4-6 mm. long. 
10. P. diversifollus. 
Peduncles of the submerged spikes not over 2 mm. long. 
11, P. spirillus. 
With submerged leaves only. 
Leaves with broad clasping blades. 6. P. richardsonil, 
Leaves narrow or capillary blades. 
Stipules free from leaves, 
Stem flattened. 
Leaves 5-20 cm. long, 2-4 mm. wide. 7. P. zosterifolius. 
Leaves 2-6 cm. long, 1 mm. or less wide. 8. P. foliosus. 
Stem filiform; leaves 7 mm. wide. , 9. P. pusillus. 
Stipules adnate to the base of the leaves. 
Stem flattened; stigma broad, sessile. 13. P. interior. 
Stems filiform; stigma capitate, style evident. 
Fruit not keeled. 12. P. pectinatus. 
Fruits prominently keeled, 14. P. interruptus. 
1. Potamogeton natans L. 
In ponds and streams throughout the state. 
2. Potamogeton amphifolius Tucherm. 
In streams and ponds, mostly in the eastern part of the state. Atkin- 
son; Cedar County; Grant County; Lincoln; Neligh. 
3. Potamogeton alpinus Balbis. 
Reported only from Cass County. 
4. Potamogeton lonchitis Tuckerm. 
Potamogeton americanus C. & §S. 
In ponds and streams throughout the state. Anselmo; Atkinson; 
Cedar County; Minden; Neligh; Norway; Thedford. 
5. Potamogeton heterophyllus Schreb, 
Kennedy, 
5a. Potamogeton heterophyllus graminifolius (Fries.) Morong. 
In the North Loup River in Cherry County. 
6. Potamogeton richardsonii (Benn.) Rydb. 
Potamogeton perfoliatus richardsonii A. Bennett. 
Reported only from the northwestern part of the state. Atkinson; 
Whitman. 
7. Potamogeton zosterifolius Schum, 
In ponds or streams. Fremont; Greeley Center; Neligh. 
8. Potamogeton foliosus Raf. 
Common in ponds and streams, Lincoln; Long Pine; Neligh; Pad- 
dock; Thedford; Valentine. 
9. Potamogeton pusillus L. 
In ponds and streams in the sand-hills, Atkinson; Crawford; Swan 
Lake; Thedford. : 
10. Potamogeton diversifolius Raf, 
Potamogeton hybridus Michx, 
Lincoln; Springview. 
11. Potamogeton spirillus L. 
Potamogeton dimorphus Raf. 
Lincoln. 
