7 6 



ZANNICHELLIACEAE. 



Vol. I. 



2. Potamogeton Oakesianus Robbins. Oakes' Pondweed. Fig. 175. 



Potamogeton Oakesianus Robbins in A. Gray, Man. 

 Ed. s, 48S. 1867. 



Stems very slender, often much branched from 

 below. Floating leaves elliptic, mostly obtuse, 

 rounded or slightly subcordate at the base, 1/-2' 

 long, s"-9" wide, 12-20-nerved; petioles 2'-6' 

 long; submerged leaves mere capillary phyllodes, 

 often persistent through the flowering season ; 

 peduncles i'-$' long, commonly much thicker than 

 the stem, mostly solitary; spikes cylindric, J'-i' 

 long; stipules acute, hardly keeled; fruit obovoid, 

 about ij" long, 1" thick, nearly straight on the 

 face, 3-keeled, the middle keel sharp ; style apical 

 or subapical; sides of the nutlet not pitted, but 

 sometimes slightly impressed ; embryo circle in- 

 complete, the apex pointing toward the base. 



In still water, Anticosti to Wisconsin and New 

 Jersey. Summer. 



3. Potamogeton amplifdlius Tuckerm. Large-leaved Pondweed. Fig. 176. 



Potamogeton amplifoliits Tuckerm. Am. Journ. Sci. 



(II.) 6: 225. 1848. 

 Potamogeton amplifolius ovalifolius Morong ; A. 



Benn. Journ. Bot. 42: 70. 1904. 



Stems long, simple or occasionally branched. 

 Floating leaves oval or ovate, abruptly pointed at 

 the apex, rounded at the base, 2'-^' long, i£'-2' 

 wide, many-nerved; petioles 3'-$' long; submerged 

 leaves mostly petioled, the uppermost often elliptic 

 or oval, 3'-6' long, i'-2j' wide, the lowest lanceo- 

 late, often 8' long, with the sides closed and as- 

 suming a falcate shape ; stipules tapering to a 

 long sharp point, sometimes 4' long; peduncles 

 thickened upward, 2'-8' long; spikes cylindric, 

 1 '-2' long; fruit 2"-2j" long, ii" thick, turgid, 

 the pericarp hard, obliquely obovoid, 3-keeled; 

 face more or less angled ; style subapical ; embryo 

 slightly incurved. 



In lakes, Ontario to British Columbia, south to 

 Georgia and Nebraska. July-Sept. 



4. Potamogeton ptilcher Tuckerm. Spotted 

 Pondweed. Fig. 177. 



Potamogeton pulcher Tuckerm. Am. Journ. Sci. 45 : 

 38. 1843. 



Stems simple, terete, black-spotted, i°-2° long. 

 Floating leaves usually massed at the top on short 

 lateral branches, alternate, ovate or round-ovate, 

 subcordate, 2-44' long, o/'-3i' wide, many-nerved ; 

 peduncles about as thick as the steam, 2'-4' long, 

 spotted ; submerged leaves of 2 kinds, the upper- 

 most pellucid, lanceolate, long-acuminate, undu- 

 late, 3'-8' long, 6"-i8" wide, tapering at the base 

 into a short petiole, 10-20-nerved ; the lowest 

 much thicker, opaque, spatulate, oblong or ovate, 

 on petioles ¥-4 long; stipules obtuse or acumi- 

 nate,_ 2-carinate; fruit 2"-2i" long, il" thick, 

 turgid, tapering into a stout apical style, the back 

 sharply 3-keeled; face angled near the middle, 

 with a sinus below; embryo coiled. 



In ponds and pools, Massachusetts to Georgia and 

 Arkansas. July. 



