28 NAIADACEAE. 



uppermost opposite, frequently of two kinds, the floating ones broad, the sub- 

 merged uarrower and often thread-like or Linear; stipules present, often sheath- 

 ing the stem. Flowers in spikes or heads, which are borne on axillary pedun- 

 cles and enclosed in the bud by stipular sheaths. Sepals I, with short (daws. 



Stamens I, inserted on the base of sepals. Ovaries 4. ((J reek potamos, a river, 

 and geiton, a neighbor, on account of the aquatic habit.) 

 .1. Stipules axillary and free from the leaf. 

 Plants with both submerged and floating leaves; submerged leaves linear <>r lanceolate, 



bearing true blades I. /'. americanus. 



Plants with leaves all submerged. 



Leaves with broad blades _'. /'. lucens. 



Leaves very narrow, thread-like or setaceous. 



Without propagating buds or glands 3. P. foliosus. 



With both propagating buds and glands 4. /'. pusillus. 



B. Stipules adnate to the leaf or petiole; submerged lea-res only. 



Leaves capillary 5. P. pectinatus. 



Leaves flat, y 2 to \ l / 2 lines broad 6. P. latifolius. 



1. P. americanus C. & S. Stems terete, much branched, ."> to (i ft. Long; 

 floating leaves coriaceous, elliptical, 2 to 4 in. long, i/> to iy 2 in. wide, the 

 petiole often longer than the blade, submerged leaves very thin, lanceolate, 

 4 to 12 in. long, 4 to 6 lines broad, rounded at base, or tapering into a petiole 

 1 to 4 in. long; stipules 1 to 4 in. long; peduncles 2 to 3 in. long; spikes 1 to 2 

 in. long, densely fruited; nutlets obliquely obovate, l 1 /-* to 2 lines long, the 

 back 3 -keeled, with the middle keel prominent. — (P. lonchites Tuckerm.) . 



Ponds or slow creeks in the valleys or hills at low altitudes: California, 

 Washington and the Atlantic States. 



2. P. lucens L. Stem thick, branching below and bearing masses of 

 very leafy branches at summit; leaves all submerged, thin, elliptical to lanceo- 

 late or oblanceolate or the uppermost oval, acute or acuminate, often undulate- 

 serrate 1 , narrowed at base to a short petiole or sessile, 2 to 7 in. long and % 

 to l"i in. wide; stipules greenish, 1 to 2 in. long, loose and spreading, some- 

 times very broad; peduncles 3 to 6 in. long; spikes 2 to 2% in. long, thick 

 cylindrical; nutlet 1% lines long, nearly as broad, with 3 distinct ribs on back. 



Small lakes and ponds: San Francisco Peninsula to Southern California; 

 also far eastward beyond our border. 



3. P. foliosus Raf. Leafs Pondweed. Stem flattened, much branched, 

 1 to 2 ] / {. ft. high; leaves rather thickly clothing the stem, 1 to l 1 ,/* in. long. 

 !/. to 1 line wide, abruptly acute; stipules white, transparent, (i to •) lines long; 

 (lowers few in a head on a peduncle 2 to (i lines long; fruit nearly 1 line long, 

 .''.keeled on the back, the central keel with narrow rough-edged wing. — (1*. 



pauciflorous Pursh.) 



(iilroy; San Francisco ; Mariposa, Congdon; Birds Landing, J&pSOli; Shasta 



Co., Baker, northward into Oregon and far eastward. 



4. P. pusillus L. Slender Pondweed. stems filiform, branching, '•_. to 

 1 ft. long; leaves narrowly linear or often nearly setaceous, with a crater like 

 -land on each side of the Btem at base of the petiole or rarely -landless, 1 

 to 3 in. long, % to % line wide, sessile; stipules short, obtuse, becoming 

 setose; peduncles flattened, Blender, '•_■ to 3 in. long; spikes interrupted or capi- 

 tate; nutlet obliquely elliptical, :i i to l I'm.' long, with a groove on each side 



of the rounded back, or sometimes with 3 distinct keels, beaked by a short 

 style. 



Santa Cruz, San I'ra ncisco, and Sierra Nevada (ace. Hot. Cal.), to Oregon 

 and eastward to the Atlantic States. 



