l\>tamn(jdnn. NAIADACE.E. 295 



Stem stout, flcxiious a])ovc : kavos laticcolato, obtusp, cucullatf* at the 

 apex, rounded and sessile at base : fruiti. large, senucireulitr, 

 beaked. 8. P. pi:^;i,ONr,us. 



Stem slender, straight : leaves lanceolate, acuminate, clasping : sti- 

 pules small : fruit nearly orbicular. 9. P. PEUFOLrATU.s. 

 Leaves all submerged, sessile, narrowly linear or setaceous. 

 Stipules free from the narrow base of the leaf. 

 Spike linear-cylindric. 

 Stem flattened : leaves gra.ss-likc, 3-nervcd, clasping : stipules 



conspicuous : peduncle longer than the spike : fruit large. 10. P. zostervefolius. 

 S])ikc capitate (or intcurupted in n. 1:5) : stems very slender. 



Leaves very narrow, 1 or 2 inelies long, ] - 3-nerved, narrowed at 



base : peduncles very short : fruit small, undtdate-carinate. 

 Leaves larger, 2 or 3 inches long by a line wide or less, 3-5- 



iierved. 



Leaves narrowly linear, 1 or 2 inches long, sessile, 1 - 5-nervcd : 



peduncles long, slender : fruit more obscurely keeled. 



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



Stem filiform : leaves very narrowly linear or setaceous, 2 to G 



inches long, 1 - 5-nerved : peduncles long : fruit large, acute. 



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



tipped with the broad stigma. 

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

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

 acutely beaked. 



* Floating leaves more or less coriaceous, with a dilated petioled blade (the ttpper- 

 viost approximate and often opposite), different in form from the thinner siib- 

 merged ones ; stijndes free : spikes cylindrical, viostlij dense, not interrupted. 



•1— The submerged leaves reduced to narrowly grass-like or filiform sessile 



phyllodia. 



1. P. natans, Linn. Stem rather stout, simple or spariii^'Iy bninclicd : floating 

 leaves thick, ovato-clliptic to lanceolate, acutish, slightly cordate at base, 21-29- 

 iierved, usually 2 or 3 inches long, mostly shorter than the petiole ; stipules long 

 and conspicuous, acute or acuminate; upi)er submerged leaves with a small lanceo- 

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

 row thickish elongated phyllodia : peduncle stout, bearing an emersed spike I J or 

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

 small deep i)it on each side : embryo nearly circular. — lieichenb. Icon. Fl. Germ. 

 V\\. 26, t. 50. 



In ponds and ditches ; Plumas County {Mn^. Austin) and northward to Washington Territory 

 {LyaU, Hall, Ifonr.n)sim\ Sitka, in Northern Nevada and Utah {jrafsoii), and common eastward; 

 also Euro|)ean and Asiatic. Fruit maturing in August and September; ni deeper or flowing 

 water the plant becomes more slender and often wholly submerged. 



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

 ing leaves narrowly oblong to elliptic, 11 -17-nerved, obtuse or acutish, atteimate 

 behjw into a flattened petiole usually shorter than the (1 to 2h inches long) blade; 

 stipules sheathing, soon deciduous, an inch long or less ; submerged loaves very thin, 

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

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

 l)eduncles : fruit obovate, 3-kcelcd, slightly apiculate, li lines long or less : nutlet 

 slightly de[)ressed on the sides: embryo spirally incurved, forming about H coils. 

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



Li still or flowing water ; Yosemite Valley {Rnhindcr) ; ColiunI)ia V;illey (//'(//, HoiceU) ; com- 

 mon in the Atlantic States. 



■t- -t- Submerged leaves lanceolate, rarely oval or linear. 



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

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



