with strong crossveins, the lateral nerve usually marginal; stipules prominent, 

 2-5 cm. long, the base adnate to the leaf to form a sheath slightly wider than the 

 stem, greenish or whitish, the free portion less than half the length of the sheath; 

 peduncles 3-25 cm. long, flexuous; spikes with 2 to 5 whorls of flowers, soon 

 becoming widely and unequally spaced (moniliform), in fruit to 5 cm. long; 

 flowers sessile or nearly so; perianth greenish, the blades orbicular to elliptical, 

 1-2 mm. wide; anthers 0.5-1 mm. long; fruits obliquely obovate, plump, narrow 

 at base, rounded on the dorsal side, 2.5-4 mm. long, 2-3 mm. wide; dorsal keel 

 absent, the lateral keels obscure; beak facial, usually recurved, about 0.6 mm. 

 long; exocarp light tan. yellowish or pale-olive-green; endocarp loop solid, apex 

 of seed pointing toward the basal end or slightly above. 



In alkaline, brackish or saline water of ponds, quiet rivers, marshes and ocean 

 shores, often occurring in great masses, in most of Okla., throughout Tex. except 

 perhaps the e. Timber Belt and Blackland Prairies, and throughout most of N. M. 

 and Ariz., mature fruit from May to Oct.; throughout much of e. half of U. S. 

 and Can., w. to Alas., s. to Mex. 



4. Potamogeton crispus L. Curled pondweed. Fig. 34. 



Rhizome buff or reddish, about the same thickness as the stem; stem simple 

 or branched, laterally compressed and somewat 4-angled with the broader sides 

 furrowed, 0.5-2.5 mm. in greatest diameter; stele of the oblong-type pattern with 

 but 1 central bundle and 1 lateral bundle on each side; endodermis of 0-cells; 

 interlacunar bundles absent; subepidermal bundles absent; pseudohypodermis 1 

 cell thick; leaves all submersed, bright-green to dark-green or occasionally slightly 

 reddish, translucent, linear-oblong to linear-oblanceolate, to 1 dm. long and 

 1 cm. wide, the apex broadly rounded, the base semiclasping; nerves 3 to 7, the 

 laterals close to the margin; lacunae of 1 or 2 rows on each side of midrib; 

 margins finely and irregularly dentate and often undulate; stipules 5-15 mm. long, 

 slightly adnate at base, the upper part fraying early to leave papery or shreddy 

 bases; peduncles 2-7 cm. long; spikes of 3 to 5 whorls of flowers, compact or 

 moniliform, in fruit 1-2 cm. long, 1-1.3 cm. wide; flowers sessile or on very 

 short pedicels; perianth blades orbicular, 1.2-2.1 mm. wide; anthers 0.7-1.3 mm. 

 long; fruits ovate, 2-3.6 mm. long (excluding beak), 1.5-2.8 mm. wide; keels 

 obtuse but prominent, the dorsal one strongly developed below and with a small 

 tooth near the base; beak prominent, straight or incurved, as long as the fruit 

 body; exocarp dark-olive or brownish; endocarp loop solid and near the base; apex 

 of seed pointing toward the basal end; winter-buds burlike, hard and horny, 1-2.5 

 cm. thick. 



In ponds and streams, often abundant in quiet muddy calcareous water; seldom 

 found fruiting but does not produce fruits in shallow warm non-fluctuating water, 

 in Okla. (Alfalfa, Choctaw, Comanche, Garfield and Ottawa cos.), Tex. (Dallas, 

 Grayson, Hemphill, Randall and Travis cos.), N. M. (Hidalgo and Taos cos.) and 

 Ariz. (Yavapai Co.), Apr.-Aug.; nat. of Eur. 



When thoroughly established this species may become a very aggressive weed. 



5. Potamogeton foliosus Raf. Fig. 35. 



Rhizome freely branching, rooting at the nodes; stem subsimple below, much- 

 branched above, filiform, laterally compressed, usually without glands at the 

 nodes; stele of the one-bundled-type; endodermis of 0-cells; interlacunar bundles 

 absent; subepidermal bundles present; pseudohypodermis absent; leaves all sub- 

 mersed, narrowly linear, green to bronze, to 1 dm. long and 2.7 mm. wide, 

 slightly tapering to a sessile base, entire-margined, acute or subacute at apex; 

 nerves 3 to 5, the midrib prominent, without bordering lacunae or with 1 to 3 

 rows on each side at the base, lateral nerves joining the midrib 1 to 3 leaf-widths 

 below the apex, in broad leaves with 5 nerves the marginal ones may join the 



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