86 



ZANNICHELLIACEAE. 



Vol. I. 



30. Potamogeton dimorphus Raf. Spiral 

 Pondweed. Fig. 203. 



Potamogeton dimorphus Raf. Month. Mag. Crit. Rev. 



1: 358. 1817. 

 Potamogeton Spirillus Tuckerra. Am. Journ. Sci. (II.) 



6: 228. 1848. 

 Potamogeton Spirillus curvifolius Peck, N. Y. Stale 



Mus. Rep. 49: 28. 1896. 



Stems compressed, branched, 6'-2o' long, the 

 branches often short and recurved. Floating leaves 

 oval or elliptic, obtuse, the largest about 1' long and 

 ¥ wide, with 5-13 nerves deeply impressed beneath, 

 their petioles often 1' long; submerged leaves linear, 

 iJ"-2" long, about i" wide, mostly 5-nerved; stipules 

 of the upper floating leaves free; those of the sub- 

 merged leaves adnate to the blade or petiole ; spikes 

 above water 3"-s" long, continuous, the lower mostly 

 sessile, capitate and 1-10-fruited ; fruit cochleate, 

 roundish, less than 1" long, flat and deeply impressed 

 on the sides, 3-keeled on the back, the middle keel 

 winged and rarely 4-5-toothed; style deciduous;, em- 

 bryo spiral, about ii turns. 

 In ponds and ditches, Nova Scotia and Ontario toMinnesota, south to Virginia, Missouri and 

 Nebraska. June-Aug. 



31. Potamogeton filiformis Pers. Filiform 

 Pondweed. Fig. 204. 



Potamogeton filiformis Pers. Syn. 1 : 152. 1805. 

 Potamogeton filiformis Macounii Morong ; Macoun, Cat. 



Can. PI. 4: 88. 1888. 



Stems from a running rootstock, slender, 3°-20° 

 long, filiform above, stout and thick towards the 

 base. Leaves numerous, 2'-i2' long, i"-i" wide, 

 i-nerved with a few cross veins ; sheaths about 2" 

 long and the free part of the stipule shorter, scarious 

 on the edges ; flowers on long, often recurved pedun- 

 cles, 2-12 in each whorl, the whorls i'-i' apart; fruit 

 i"-ii" long, slightly less than i" wide, the sides even, 

 the back not keeled, the face nearly straight or ob- 

 tusely angled near the top ; stigma nearly or quite 

 sessile, remaining on the fruit as a broad truncate 

 projection. Embryo a complete spiral, the curved 

 apex pointing inside the base. 



In ponds and lakes, Anticosti to western New York 

 and Montana. August. 



32. Potamogeton interior Rydb. Inland 

 Pondweed. Fig. 205. 



Potamogeton interior Rydb. Fl. Colorado 13. 1906. 



Potamogeton marinus occidentalis Robb. Bot. King's 

 Exp. 339. 1871. 



Potamogeton filiformis occidentalis A. Benn. Ann. Con- 

 serv. Jard. Genev. 9: 102. 1905. 



Stem slender, much branched and longer than in 

 the preceding; leaves all submerged, capillary or 

 narrowly linear, with an acute or more or less pun- 

 gent apex, 2'-6' long, i"-$" wide, mostly i-nerved; 

 stipules adnate to the leaf-bases, the sheath at least 

 7" long, the free part shorter; spikes few-flowered, 

 often interrupted, $'-3!' long ; peduncles as thick as 

 the stem, ii'-/ long; nutlets sometimes slightly 

 pitted, without keels or inconspicuously i-keeled; 

 style almost invisible; embryo an incomplete spiral, 

 the straight apex pointing directly towards the base. 



Ontario to the Northwest Territory, south to Utah 

 and Colorado. 



