young, acutish with age, 2-5 cm. long, 2-keeled; peduncles 5-1 1 cm. long; spikes 

 with about 10 whorls, in fruit 2-3.5 cm. long, 8-11 mm. thick; flowers sessile or 

 nearly so; perianth greenish, blades orbicular to elliptical and 1.2—3 mm. wide; 

 anthers 0.8-1.4 mm. long; fruits obliquely ovate, rounded or cuneate at base, the 

 sides flat or slightly concave, 2.7-4 mm. long, 2.3-3.4 mm. wide; keels usually 

 prominent, acutish, the dorsal one often strongly developed and sometimes with 

 a basal lobe projecting below the point of attachment; beak often prominent, to 

 0.8 mm. long; exocarp light-brown to olive-green; endocarp with 3 prominent 

 acutish and somewhat muricate keels; beak linear, facial, about 1 mm. long; loop 

 solid; apex of seed pointing 0.5-1.2 mm. above the basal end. 



In muddy pools, boggy streams, lakes and occasionally in clear water in sandy 

 bottoms in Okla. (McCurtain, Payne and Pushmataha cos.) and in Tex. mostly 

 in the Timber Belt^ flowers in Apr. and May, mature fruit by mid-May; in the 

 e. half of U. S. 



11. Potamogeton amplifolius Tuckerm. Fig. 41. 



Plant froni stout rhizomes; stems simple or branched near the top^ often rufous; 

 submersed leaves variable, from short-lived (lanceolate and short-petioled) to 

 persistent (broadly lanceolate to ovate and folded along the midvein), the blade 

 8-20 cm. long, 25-75 mm. broad, tapering to petiole 1-6 mm. long, the stipules 

 becoming fibrous and stringy, 3-10 cm. long; floating leaves similar to the upper 

 submersed leaves to ovate or elliptic, round-tipped, rounded or tapering to the 

 base, 5-10 cm. long, 25-50 mm. wide, the stipules usually 2-keeled; peduncles 

 often thickened apically, 5-11 cm. long; spikes with 9 to 16 whorls of flowers, 

 4-8 pm. long when mature; nutlets 3-5 mm. long, obovate, rounded on back, 

 cuneate at base, the sides flat, the beak prominent. 



Lakes, ponds, still water of creeks, at middle and lower altitudes, in rather deep 

 water, in Okla. (Comanche, McCurtain and Osage cos.), Apr.-Sept.; from Nfld. 

 to B. C, s. to Va., Ark., Okla., and Calif. 



12. Potamogeton nodosus Poir. Fig. 42. 



Rhizome white, suffused or spotted with rusty red; stem simple, terete, often 

 pressing very flat, 1-2 mm. in diameter; stele with the triotype pattern, with the 

 phloem on the inner face of the trio-bundle appearing as one patch; endodermis 

 of 0-cells; interlacunar and subepidermal bundles absent; pseudohypodermis 

 absent; submersed leaves thin, linear-lanceolate to broadly lance-elliptic, to 2 dm. 

 long and 35 mm. wide, tapering gradually at base into a petiole 2-13 cm. long, 

 tapering gradually to an acutish but not sharp-pointed apex; nerves 7 to 15; 

 lacunae of 2 to 5 rows along the midrib; margin of young blades with fugacious 

 translucent denticles; floating leaves coriaceous, with long petioles; blades lenticu- 

 lar to elliptic, cuneate or somewhat rounded at base, acutish to rounded at apex 

 and sometimes with an obtuse mucro, to 11 cm. long and 45 mm. wide; nerves 

 9 to 21; lacunae rarely present; stipules of submersed leaves brownish, often 

 delicate and decaying early, linear, acute or obtuse, 3-9 cm. long, those of the 

 floating leaves similar but usually broader at base and more or less 2-keeled; 

 peduncles usually thicker than the stem, 3-15 cm. long; young spikes compact 

 but becoming loose at anthesis, of 10 to 17 whorls of flowers, at maturity usually 

 not densely fruited, 3-7 cm. long, 8-10 mm. thick; flowers sessile; perianth 

 greenish or brownish, orbicular or elliptical, 1.4-2.6 mm. wide; anthers 1-1.4 mm. 

 long; fruits obovate, 3.5-4.3 mm. long, 2.5-3 mm. wide; keels prominent, the 

 dorsal strongly developed (especially upward), the laterals often muricate; beak 

 facial, short; exocarp of mature fruits brownish or reddish; endocarp with keels 

 strongly developed, the dorsal often 0.5 mm. wide, the laterals strongly muricate; 



111 



