198 NAIADACE^E. Potamogeton. 



very acute and mucronate, narrowed to the eubpetiolate base : otherwise like the 

 last, of which it is scarcely more than a variety. Arner. Journ. Sci. 2 ser. vii. 354. 



Walker's Basin (Rothrock, n. 292) ; in the Atlantic States, from the Great Lakes to South Caro- 

 lina, but not common. 



13. P. pusillus, Linn. Stem filiform, branching: leaves narrowly linear, 1 or 2 

 inches long, rarely a line wide, often nearly setaceous, 1 5-nerved, obtuse and 

 mucronate or acute, biglandular at base and sessile ; stipules obtuse, becoming setose : 

 spikes capitate, or somewhat elongated and open, or interrupted, on slender flattened 

 peduncles to nearly 2 inches long : fruit as in the preceding, but more obscurely 

 and obtusely keeled : embryo less incurved. Eeichenb. 1. c., t. 22. P. trichoides, 

 Benth. PI. Hartw. 341. 



In pools and ditches ; near Santa Cruz (Hartweg, n. 2016) and at Soda Springs on the Upper 

 Tuolumne (Bolander), the form with subsetaceous acute or cuspidate leaves, distinguished as var. 

 teimissimus, Mert. & Koch. The typical European form occurs in the northern Atlantic States 

 and in British America. 



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



14. P. pectinatus, Linn. Stem filiform, repeatedly branched : leaves very 

 narrowly linear, 2 to 6 inches long, rarely over half a line broad, often setaceous, 

 1 -nerved, acute : peduncles elongated, slender : spikes ^ to 2 inches long : fruit in 

 often dense verticils, large (2 lines long), obliquely obovate, compressed, obtusely 

 keeled, acute: nutlet very thick: embryo spirally incurved. Reichenb. 1. c. 11, 

 t. 19. 



Var. (?) latifolius, Robbins. Stem stouter: leaves short and broader (1 or 2 

 inches long by a line or two broad), 3 - 5-nerved with numerous transverse veinlets, 

 acute or obtuse : sheaths large, with scarious margins, exceeding the obtuse scarious 

 stipules. Bot. King Exp. 338. 



In various parts of California (Chamisso, Coulter, Douglas) ; Santa Barbara (Mrs. Elwood Cooper) ; 

 Oregon and Washington Territory (Lyall, Hall) ; Northern Nevada and Utah ( Watson), and Com- 

 mon in the Atlantic States as well as in Europe. The variety has been collected in King's River 

 and at Gulling's Hot Spring, Lassen County (Lemmon), and in the lower Hum bold t River 

 ( Watson) ; it appears to scarcely differ from the European marine species P. zosteraceus, Fries, to 

 which it might perhaps well be referred. 



15. P. marinus, Linn. Resembling narrow-leaved forms of the last species, 

 low and very leafy : peduncles much elongated : fruit much smaller (a line long) and 

 thinner, round-obovate, not keeled upon the rounded back, tipped with the broad 

 sessile stigma : embryo annular. 



Var. (?) occidentalis, Robbins. Often taller and less leafy : peduncles usually 

 rather short : spikes interrupted : nutlet slightly 3-keeled. Bot. King Exp. 339. 



The variety only has been collected in Truckee River and Ruby Lake, Northern Nevada ( Wat- 

 80*11), and is apparently a common species of the interior eastward to Montana (Richardson) and 

 Colorado (Hall & Harbour), sometimes nearly approaching European forms. 



16. P. Robbinsii, Oakes. Stem rather stout, often much branched and fre- 

 quently flexuous : leaves numerous, distichous, the close sheaths nearly covering the 

 stem, linear-lanceolate, 2 to 3 inches long by 2 lines broad, many-nerved, acuminate, 

 ciliate-serrulate ; stipules obtuse, becoming setose : spikes usually several, on rather 

 stout pedicels about an inch long, loose and more or less interrupted, about half an 

 inch long : fruit oblong-obovate, nearly 2 lines long, keeled with a broadish wing, 

 acutely beaked : embryo stout, ovally annular. Hov. Mag. vii. 1 78 ; Robbins, in 

 Gray's Manual, 490. 



In ponds and slow streams ; not yet found in California, but to be expected ; Oregon (Hall); 

 Yellowstone region (C. Richardson) ; common in the northern Atlantic States. 



Scanty specimens of what seems to be an undescribed species of this group have been collected 

 in Pyramid Lake (Miss S. A. Plummer), without flowers or fruit. The stem is broad and flat- 

 tened ; the leaves thick, 6 inches long by 1 lines broad, 3-nerved with transverse veinlets, con- 

 spicuously sheathing and with broad stipules. 



