Potamogeton. NAIADACE^E. 195 



P. PKiELOXGUS. 



Stem stout, flexuous above : leaves lanceolate, obtuse, cucullate at the 

 apex, rounded and sessile at base : fruit large, senucircuiar, 

 beaked. . , . ,. 



Stem slender, straight : leaves lancex)late, acuminate, clasping : sti- „„„,.„, ...p,., 



pules small : fruit nearly orbuailar. 9. I . PEKiOLlAPL^. 



Leaves all submerged, sessile, narrowly linear or setaceous. 

 Stipules free from the narrow base of the leat. 



Spike linear-cylindric. , , . , . , 



Stem flattened: leaves grass-like, 3-nerved, clasping : stipules ,^,™^p ^„.,„,. 



conspicuous : peduncle longer than the spike : truit large. 10. P. zoster.efolils. 

 Spike capitate (or interrupted in n. 13) : stems very slender. 



T paves verv narrow, 1 or 2 inches long, 1 - 3-nerved, narrowed at 



Tase peduncles very short: fruit small, undulate-carinate. 11. P. tauciflokus. 

 Leaves larger, 2 or 3 inches long by a line wide or less, 3 - 5- ^^^ ^ ^^^^XK^^i^xr,. 



nerved. , ., , _ i "" ' 



Leaves narrowly linear, 1 or 2 inches long sessile, 1 - 5-nerved : p,.,„LUs 



peduncles long, slender : fruit more obscurely keeled. 13. P. PUSiLLUb. 



Stipules united with the sheathing base of the leaf : spikes interrupted 



Stem filiform: leaves very narrowly linear or setaceous, 2 to b ^^,,^,^,.ry. 



inches loner, 1- 5-nerved : peduncles long : fruit large, acute. 14. P. PECTIN A rbS. 

 Similar: leaves setaceous : peduncles usually short: fruit small, ^,,^,^,,^ 



tipped with the broad stigma. 15- i • MARINUS. 



Stem -stouter : leaves many, distichous, linear-lanceolate, shorter, 



many-nerved : peduncles short, stout : fruit large, keeled, ^^^^.^^^ 



acutely beaked. • ' 



* Floatinn leaves more or less coriaceous, ivith a dilated petloled blade {the upper- 

 most approximate and often opposite), different In form from thetJunnersicb- 

 mergedones; stipules free : spikes cylindrical, mostly dense, not interrupted. ^ 

 ^ The submerged leaves reduced to narrowly grass-like or filiform sessile 



p)hyllodla. 



1 P. natans, Linn. Stem rather stout, simple or sparingly branched : flofiting 

 leaves thick, ovate-elliptic to lanceolate, acuti.sh, slightly cordate at base, -^1-^9- 

 nerved, usually 2 or 3 inches long, mostly shorter than the petio e ; stipules long 

 and conspicuous, acute or acuminate; upper submerged leaves with a small lanceo- 

 late blade, tlie lower (only formed early or late in the season) reduced to very nar- 

 row thickish elongated phyllodia : peduncle stout, bearing an emersed spike 1^ or 

 2 inches long : fruit turgid, obliquely obovate, acute, 2 lines long : nutlet with a 

 small deep pit on each side: embryo nearly circular. — Reichenb. Icon. Fl. Gerin. 

 vii. 26, t. 50. 



In ponds an<l ditches ; Plumas County {Mrs. Austin) and northward to Washington Territory 

 iL^arHall, Howell) and Sitka, in Northern Nevada and Utah (JVatson), ^^T;-^^ ^^^^ 

 also European and Asiatic. Fruit maturing in August and September; in deepei oi flowing 

 water the plant becomes more slender and often wholly submerged. 



2 P Claytoni, Tuckerman. Stem compressed, from creeping rootstocks : float- 

 ino- 'leaves narrowly oblong to elliptic, 11 - 17-nerved, obtuse or acutish, attenuate 

 below into a flattened petiole usuaUy shorter than the (1 to 2| inches long) blade ; 

 stipules sheathing, soon deciduous, an inch long or less ; submerged leaves very tJiin, 

 linear (2 to 5 inches long by 1 to 21 lines wide), 5-nerved, with a close cellular re- 

 ticulation between the middle nerves : spikes l to 1 inch long, on short stout 

 peduncles: fruit obovate, 3-keeled, slightly apiculate, U lines long or less : nutlet 

 slightly depressed on the sides : embryo spirally incurved, forming about 1-^ coils. 

 — ^Amer. Journ. Sci. xlv. 38, and 2 ser. vi. 227. 



In still or flowing water ; Yosemite Valley (Bolander) ; Columbia Valley {MaU, Hoioell) ; com- 

 mon in the Atlantic States. 



^ j^ Submerged leaves lanceolate, rarely oval or linear. 

 3 P rufescens, Schrad. Floating leaves (often wanting) rather thin 11 - 17- 

 nerved, narrowly oblong-elliptic or oblanceolate, 2 to 4 inches long, acutish, attenu- 



