50 Karl M. Wiegand and Arthur J. Eames 



12. P. dimorphus Raf. (P. Spirillus of Cayuga Fl.) 

 Shallow water, in sand; rare. Fr. Aug. 



Cayuta Lake, e. side (D.). 



Newf. to Minn, and Calif., southw. to Va., W. Va., and Nebr., including the 

 Atlantic Coastal Plain. 



13. P. epihydrus Raf. (P. Claytonii of Cayuga Fl. P. pennsylvanicus Willd. P. 

 Nuttallii C. & S.) 



Still shallow pools and lake margins ; frequent. Fr. Aug.-Sept. 



Spencer Lake; Cayuta Lake (D.) ; Caroline; Stewart Park; and elsewhere. 



Newf. to B. C, southw. to S. C. and Iowa, including the Atlantic Coastal Plain. 



13a. P. epihydrus Raf., var. cayugensis (Wiegand) Benn. 

 In situations similar to the preceding ; less frequent. Fr. Aug.-Sept. 

 Spencer Lake ; Summit Marsh ; Renwick ; and elsewhere. 

 Lab. to Wash., southw. to N. Y., Mich., and Iowa. Found also in Japan. 



14. P. compressus L. (P. zosterifolius Schum. and of Cayuga Fl.) 

 Small or large lakes, and mill ponds; frequent. Fr. July-Sept. 



Summit Marsh (D.) ; Dryden Lake (D.) ; Lake Como (Locke Pond, D.) ; Red 

 Mill Pond (D.) ; Malloryville (D.) ; Beebe Lake; Renwick; Cayuga Marshes. 



N. B. to B. C, southw. to Md., the Great Lakes, Iowa, and Oreg. ; rare or 

 absent on the Atlantic Coastal Plain. Found also in Eurasia. 



15. P. Friesii Rupr. (P. pusillus, var. major, of Cayuga Fl.) 

 Shallow water ; scarce. Fr. Aug.-Sept. 



Summit Marsh (D. in C. U. Herb.) ; Spencer Lake (L. Griscom & E. Moore) ; 

 s. w. part of Cayuga Lake (D. in C. U. Herb.) ; near mouth of Fall Creek (D.) ; 

 Cayuga Bridge (D.). 



S. Lab. to B. C, southw. to N. S., Conn., N. Y., Mich., Iowa, and Wash. ; doubt- 

 fully occurring on the Atlantic Coastal Plain. Found also in Eu. 



16. P. Hillii Morong. 



Pools, ditches, and shallow lake margins; "not uncommon" (D.). Fr. July- Aug. 

 Dryden Lake (D.) ; Red Mill Pond (£>.) ; pools n. and s. of Ithaca (£>.) ; Inlet 

 (D.) ; Myers Point (D.). Not found in recent years, perhaps overlooked. 

 Conn, to cent. Ont. and Wis., southw. to Pa. and Mo. ; chiefly inland. 



17. P. obtusifolius Mert. & Koch. 



Shallow water of ponds and streams ; rare. Fr. Aug. 



" Summit Marsh, in the shallow water not far from the northernmost island, where 

 it occurs but sparingly" (D.) ; Spencer Lake (E. Moore). 



E. Que. to Athabasca, southw. to Pa., Mich., Wis., and Wyo. ; of doubtful occur- 

 rence on the Coastal Plain. Found also in Eurasia. 



18. P. pusillus L. 



Ditches, pools, and lake borders ; frequent. Fr. July-Sept. 



Danby; Spencer Lake; Freeville ; Mud Pond, McLean Bogs; near mouth of Fall 

 Creek (£?.!); Cayuga; pool, Cato. 



Que. to B. C, southw. to N. E., cent, and w. N. Y., N. Mex., Ariz., and Calif. ; 

 apparently infrequent on the Atlantic Coastal Plain. Found also in Eurasia. 



True P. pusillus is a plant chiefly of brackish or limy waters. The var. tenuissi- 

 mus, inhabiting fresh and acid waters, has been found in Cortland and Oswego 

 Counties, but not within the Cayuga Lake Basin. It differs in its narrower leaves 

 (0.4-1.4 mm. instead of 1-2 mm.), more obscure lateral nerves, shorter peduncles 

 (0.5-2 cm. instead of 1.5-8 cm.), and shorter mature spikes (3-5 mm. instead of 

 5-12 mm.). 



